P. elisabethae. The “P.” is short for the genus Pseudopterogorgia. See sea whip extract.

PABA. See para-aminobenzoic acid (PABA).

padimate O. Sunscreen agent that protects skin primarily from the sun’s UVB rays (Sources: http://www.photodermatology.com/sunprotection.htm; and Skin Therapy Letter, 1997, volume 2, number 5, http://www.dermatology.org/skintherapy).

Padina pavonica extract. See algae.

Paeonia albiflora extract. See peony flower.

Paeonia suffruticosa extract. See peony root extract.

palm oil. Has emollient and antioxidant properties for skin (Source: Free Radical Biology and Medicine, 1997, volume 22, number 5, pages 761–769). See antioxidant and natural moisturizing factor (NMF).

Palmaria palmata extract. Extract from a type of algae whose common name is dulse. See algae.

palmarosa oil. See geranium oil.

palmitic acid. Detergent cleansing agent that also creates foam and can be drying. See surfactant.

palmitoyl pentapeptide 3. Trade name Matrixyl, a fatty acid mixed with amino acids. The only research showing this has any significance for skin was carried out by the ingredient manufacturer, Sederma. In their research, three different “half-face” studies with a total of about 45 participants showed it to be better than a retinol or vitamin C product (Source: Journal of Cosmetic Science, January–February 2001, pages 77–78). Without independent substantiation, however, there is no way to know how accurate this company-funded research is. Further, according to Sederma’s research, the recommended concentration for this ingredient is 3% to 5% and there are few, if any, lines that include more than just a trace amount in their products. See amino acid and fatty acid.

Panax ginseng root extract. Root extract that may have potent antioxidant properties (potentially anti-cancer) and may promote wound healing. Whether or not it can have an impact on cellulite is unknown (Sources: Journal of Agricultural and Food Chemistry, April 2006, pages 2558–2562; Phytotherapy Research, January 2005, pages 65–71; Archives of Pharmacal Research, February 2002, pages 71–76; and Cancer Letters, March 2000, pages 41–48).

Panicum miliaceum. See millet seed extract.

pansy extract. Extract for which there is a small amount of research showing it has anti-inflammatory and antioxidant properties (Source: http://www.naturaldatabase.com).

pantethine. Also known as pantothenic acid. See pantothenic acid.

panthenol. Alcohol form of vitamin B. See pantothenic acid.

pantothenic acid. Also called vitamin B5, and often touted as being effective for acne. However, there is only one study supporting this notion and it dates from the early 1980s (Source: International Journal of Dermatology, 1981, volume 20, pages 278–285). There is no current research showing this to be an effective treatment for acne, but there is a small amount of research showing that it can be effective for hydration and wound healing (Source: American Journal of Clinical Dermatology, 2002, volume 3, number 6, pages 427–433).

papain. Enzyme extracted from papaya. Applied topically, papain can cause severe irritation, itching, and allergic reactions (Source: http://www.naturaldatabase.com). There is one study showing it may be effective for exfoliation, but only in a pure concentration (Source: Archives of Dermatological Research, November 2001, pages 500–507). See enzymes.

Papaver somniferum seed. Latin name for the opium poppy seed. See opium poppy seed.

papaya extract. Extract that is the source of papain, which theoretically can have exfoliating properties on skin, although the majority of the research was not performed on skin. Papaya can be a skin irritant. See enzymes.

para-aminobenzoic acid (PABA). Sunscreen ingredient rarely used since the 1990s because of strong potential for allergic reactions.

parabens. Group of preservatives, including butylparaben, propylparaben, methylparaben, and ethylparaben, that are the most widely used group of preservatives in cosmetics. It is estimated that more than 90% of all cosmetic products contain some form of paraben. Parabens are believed to cause less irritation than some preservatives. There is research showing that in animal models (and in vitro) parabens can have weak estrogenic activity. Whether that poses any health risk for humans who are using cosmetics is unknown. The technical findings of the study, which involved both oral administration and injection into rat skin, did show evidence of a weak estrogen effect on cells in a way that could be problematic for binding to receptor sites that may cause proliferation of MCF-7 breast cancer cells. The study concluded that “future work will need to address the extent to which parabens can accumulate in hormonally sensitive tissues and also the extent to which their weak oestrogenic activity can add to the more general environmental oestrogen problem” (Source: Journal of Steroid Biochemistry and Molecular Biology, January 2002, pages 49–60).

Does this mean you should stop buying products that contain parabens? That’s a good question, but the answer is neither simple nor conclusive, even by the standards of the study itself. This is a potentially serious issue and the FDA is conducting its own research to determine what this means for human health (Source: The Endocrine Disruptor Knowledge Base (EDKB), http://edkb.fda.gov/index.html). To keep the concern in perspective, it is important to realize that parabens are hardly the only substances that may have estrogenic effects on the body.

Any estrogen, including the estrogen our bodies produce, may bind to receptor sites on cells either strongly or weakly. So, parabens can either stimulate the receptor to imitate the effect of our own estrogen in a positive way, or they can generate an abnormal estrogen response. Ironically, plant estrogens, or phytoestrogens (such as those found in soy), also produce chemicals that mimic estrogen. It is possible that a weak plant estrogen can help the body, but it can also be possible that a strong plant estrogen can make matters worse. For example, there is research that shows coffee to be a problem for fibrocystic breast disease. The reason for this is thought to be because coffee exerts estrogenic effects on breast cells (Sources: American Journal of Epidemiology, October 1996, pages 642–644; Journal of the American Medical Women’s Association, spring 2002, pages 85–90; and http://www.som.tulane.edu/ecme/eehome/newsviews/whatsnew/archive/jan_dec2002.html).

A study in the Journal of Applied Toxicology (volume 24, issue 1, January-February 2004, pages 5–13) mentioned that “although recent reports of the oestrogenic properties of parabens have challenged current concepts of their toxicity in these consumer products, the question remains as to whether any of the parabens can accumulate intact in the body from the long-term, low-dose levels to which humans are exposed.” The study discussed the fact that traces of parabens have indeed been found in human breast tumors, but was quick to point out that it is unknown if this would be the same in healthy breast tissue. Parabens present in tumors may not be the causative factor, but rather a result, of finding parabens when cancer cells are examined. It is also important to realize that parabens are used in food products as well (Source: Food Chemistry and Toxicology, October 2002, pages 1335–1373), which could very well be the source. As yet, no one has any idea (or has evaluated) whether it is the consumption of parabens or their application to the skin that is responsible for their presence in human tissue. And no one knows what the presence of parabens in human tissue means. See preservatives.

paraffin. Waxy, petroleum-based substance used as a thickener in cosmetics.

Paraffinum liquidum. See mineral oil.

Parsol 1789. See avobenzone.

Passiflora edulis extract. See passion fruit extract.

passion fruit extract. There is no research showing this has any benefit for skin.

patchouli. Fragrant oil derived from mint. It contains eugenol and can be a skin sensitizer and irritant. See counter-irritant.

Paullinia cupana seed extract. Also called guarana, this extract is used primarily in herbal supplements and beverages as a stimulant. In animal studies (mice), it has been shown to affect fat metabolism. There is also research showing that repeated use of guarana can result in persistent increases in heart rate and blood pressure as well as in unfavorable actions on glucose and potassium homeostasis. Such effects could be detrimental in persons with hypertension, atherosclerosis, or glucose intolerance—conditions that are strongly associated with obesity. Guarana is sometimes used in cellulite products because of its theophylline and caffeine components. Research has shown it can be absorbed into the skin. Whether or not topical application can affect fat metabolism or have other associated health risks in humans is not known (Sources: International Journal of Pharmaceutics, April 2006, http://www.sciencedirect.com/; Food and Chemical Toxicology, June 2006, pages 862–867; Clinical Nutrition, December 20005, pages 1019–1028; and Clinical Pharmacology & Therapeutics, June 2005, pages 560–571).

pawpaw extract. See papaya extract.

peanut oil. Emollient plant oil similar to all nonfragrant plant oils.

pecan oil. Emollient plant oil similar to all nonfragrant plant oils.

pectin. Natural substance found in plants, especially apples, and used in cosmetics as an emulsifier and thickening agent.

PEG compound. PEG is the acronym for polyethylene glycol. Various forms of PEG compounds are mixed with fatty acids and fatty alcohols to create a variety of substances that have diverse functions in cosmetics, including acting as surfactants, binding agents (to keep ingredients blended), stabilizers, and emollients. See polyethylene glycol.

PEG-100 stearate. See PEG compound and thickening agent.

PEG-120 methyl glucose dioleate. See surfactant.

PEG-150 distearate. See thickening agent.

PEG-40 hydrogenated castor oil. Emollient ingredient that is a mixture of polyethylene glycol (PEG) with castor oil. See polyethylene glycol (PEG) and castor oil.

PEG-80 sorbitan laurate. Mild surfactant. See surfactant.

Pelargonium graveolens oil. See geranium oil.

pellitory. Plant whose root extract can cause skin irritation; its safety is unknown.

pentadecalactone. Synthetic fragrance used in cosmetics.

pentaerythrityl tetraoctanoate. Synthetic compound as an emollient and thickening agent. See thickening agent.

pentasodium pentetate. Used as a chelating agent in cosmetics to prevent various mineral components from binding together and negatively affecting the formulation.

peony flower. European flower used topically for treating a variety of skin diseases, including skin fissures (painful cracks in skin). Evidence of its effectiveness for these purposes is anecdotal. There is not enough known about the effects of peony flower to substantiate its use or safety in cosmetic products (Source: http://www.naturaldatabase.com).

peony root extract. There is research showing that the root of the peony plant can have anticancer properties as well as antioxidant properties (Sources: Cancer Letters, December 2001, pages 17–24; Archives of Pharmaceutical Research, April 2001, pages 105–108; and Chemical and Pharmaceutical Bulletin, January 2001, pages 69–72). However, there is no research showing that it has that benefit for skin (Source: http://www.naturaldatabase.com).

peppermint. Both the oil and the extract can have antimicrobial properties (Source: Journal of Agricultural and Food Chemistry, July 2002, pages 3943–3946), but they can also have an irritating, sensitizing effect on skin (Source: http://www.naturaldatabase.com). See counter-irritant.

peptide. Peptides are portions of proteins, which are long chains of amino acids. In the body, peptides regulate the activity of many systems by interacting with target cells. Enzymatic action breaks proteins into peptides so they can exert their influence on the body. Some peptides have hormonal activity, others have immune activity, some are cell-communicating ingredients that tell cells how to react and what to do, some are believed to play a role in wound healing, and still others are believed to affect the pathology of skin conditions such as atopic dermatitis and eczema.

Whether peptides have benefit when applied topically to skin for wound healing, skin-barrier repair, or as disinfectants is difficult to ascertain because they generally cannot penetrate skin and at the same time remain stable because they are too hydrophilic, or water-loving. Ironically, peptides can become unstable in water-based formulas (Sources: Biotechniques, July 2002, pages 190–192; and IFSCC Magazine, July 2004, page 153). Further, because peptides are vulnerable to the presence of enzymes, when peptides are absorbed, the abundant enzymes present in skin can break the peptides down to the point where they have no effect at all. However, the latest research is examining how different types of synthesized peptides can enter the living membrane of cells and, more interesting, transport biologically active ingredients to these cells. Some of these peptides have demonstrated a remarkable anti-inflammatory effect. Creating specific peptide chains in the lab and then attaching a fatty acid component to them allows peptides to overcome their inherent limitations: being absorbed and remaining stable. Lab-engineered peptides appear to have the kind of efficacy and benefit that go beyond the skin’s surface, but more conclusive, long-term research is essential to gain an understanding of what, if anything, is really taking place (Sources: Cosmetics & Toiletries, June 2004, page 30; Pharmaceutical Research, March 2004, pages 389–393; and The Journal of Investigative Dermatology, September 2005, pages 473–481). It is reasonable to assume that as synthetic peptide technology broadens, we will see more options for use in skin-care products promoting anti-aging properties, specifically, tissue regeneration (Source: Cosmetics & Toiletries, March 2003, pages 43–52).

For these specialized peptides to exert a benefit beyond that of a water-binding agent, three criteria must be met: the peptides must be stable in their base formula, they must be paired with a carrier that enhances absorption into the skin, and they must be able to reach their target cell groups without breaking down. Achieving this goal is no easy feat, but one that cosmetics scientists are predicting will have significant potential in the realm of anti-aging skin-care ingredients.

Persea gratissima oil. See avocado oil.

Persicaria hydropiper. Also known as water pepper. All parts of this plant extract have been shown in vitro to be not only a potent antioxidant but also able to inhibit the expression of collagen-depleting MMP-1 when applied to human fibroblast cells (Source: Journal of Cosmetic Science, January/February 2007, pages 19-32). See matrix metalloproteinases.

petitgrain mandarin. See mandarin orange oil or extract.

petrolatum. Vaseline is pure petrolatum. For some unknown and unsubstantiated reason, petrolatum has attained a negative image in regard to skin care, despite solid research to the contrary. Topical application of petrolatum can help the skin’s outer layer recover from damage, reduce inflammation, and generally heal the skin (Source: Acta Dermato-Venereologica, November–December 2000, pages 412–415). See also mineral oil.

PHA. See polyhydroxy acid.

phenoxyethanol. Common cosmetic preservative that is considered one of the less irritating ones to use in formulations. It does not release formaldehyde. See preservatives.

phenoxyisopropanol. Alcohol used as a solvent and preservative. See solvent and preservative.

phenyl trimethicone. Silicone with a drier finish than dimethicone. See silicone.

phenylalanine. See amino acid.

phosphatidylcholine. Active ingredient in lecithin. Every cell membrane in the body requires phosphatidylcholine (PC). It is also a major source of the neurotransmitter acetylcholine. Acetylcholine is used by the brain in areas that are involved in long-term planning, concentration, and focus, but all of that information is associated with ingesting PC, not putting it on the skin. PC is considered a very good water-binding agent and aids in the penetration of other ingredients into the skin. It absorbs well without feeling greasy or heavy (although other ingredients can perform similarly, including glycerin, ceramides, and hyaluronic acid) (Sources: Skin Pharmacology and Applied Skin Physiology, September–October 1999, pages 235–246; and Journal of Controlled Release, March 29, 1999, pages 207–214.) See lecithin and water-binding agent.

phosphatidylethanolamine. See phospholipid.

phospholipid. Type of lipid (fat) composed of glycerol, fatty acids, and phosphate. Phospholipids are essential to the function of cell membranes by providing a stable surrounding structure. Lecithin is an example of a phosopholipid. See glyceryl ester and natural moisturizing factor (NMF).

phosphoric acid. Used as a pH adjuster in cosmetics and skin-care products.

photosensitizer. Ingredient that can cause the skin to have an irritated or inflamed reaction when exposed to sunlight.

Phyllanthus emblica fruit extract. Extract that has antioxidant and anti-inflammatory properties (Sources: Journal of Ethnopharmacology, May 2000, pages 171–176; and Planta Medica, December 1997, pages 518–524).

phytantriol. Hair- and skin-conditioning agent that also has water-binding properties.

phytic acid. Component of plants that has antioxidant properties.

phytoestrogen. See plant estrogen.

phytonadione. One form of vitamin K. See vitamin K.

phytosphingosine. Long-chain, complex fatty alcohol that functions as a water-binding agent and also has preservative qualities. Its name is derived from the term sphingoid, coined in 1884 by chemist J. L. W. Thudichum because the way the molecules of this substance lined up reminded him of the riddle of the Sphinx. Research shows it is effective in regulating damaged or diseased epithelial cells. It seems this ingredient can also be a cell-communicating ingredient, albeit one that is best for compromised skin (Source: Journal of Investigative Dermatology, October 2003, pages 1135–1137).

phytosterol. Cholesterol-like molecules found in all plant foods; the highest concentrations are found in vegetable oils. Phytosterols in the natural diet may lower cholesterol (Sources: Annual Reviews of Nutrition, 2002, volume 22, pages 533–549; and Metabolism, May 2002, pages 652–656). However, regarding topical application, there is research showing that the high lipid content of phytosterols can make the skin extremely sensitive to light (Source: Photochemistry and Photobiology, September 1997, pages 316–325).

pine oil. Can have disinfectant properties (Source: Antimicrobial Agents and Chemotherapy, December 1997, pages 2770–2772), but it can also be a potent skin irritant and should never be used on abraded or chafed skin. May be used as an extract or oil.

pineapple extract. Contains the enzyme bromelain, which can break down the connecting layers between skin cells to exfoliate skin. However, bromelain used alone is a more effective source of exfoliation, and does not have the irritating properties of the pineapple. See bromelain.

pinecone extract. Components of this extract, specifically linolenic and linoleic acids, can have antioxidant properties (Source: Tree Physiology, June 2002, pages 661–666) and antibacterial properties for skin (Source: International Journal of Food Microbiology, May 2000, pages 3–12).

Pinus lambertiana wood extract. Pine extract that may have skin-sensitizing properties (Source: Botanical Dermatology Database, http://bodd.cf.ac.uk/index.html).

Pinus sylvestris extract. See pinecone extract.

Piper nigrum. See black pepper.

pistachio seed oil. Emollient plant oil with uses similar to peanut oil in cosmetics. See peanut oil.

Pistacia vera seed oil. See pistachio seed oil.

Pisum sativum. Latin name for the garden pea. It does have antioxidant activity, but there is no research showing that it can reduce cellulite (Source: Phytotherapy Research, October 2003, pages 987–1000).

plasticizing agents. Ingredients that place a thin layer of plastic over the skin. Typically these are used in facial masks so they can be peeled off the skin. See film-forming agent.

plum extract. Extract of Prunus americana that may have antioxidant activity when applied topically (Source: Phytotherapy Research, February 2002, pages 63–65).

Pogostemon cablin. See patchouli.

poloxamers. See surfactant.

polyacrylamide. See film-forming agent.

polyaminopropyl biguanide. Synthetic polymer that functions as a preservative.

polybutene. Polymer derived from mineral oil and used as a thickener and lubricant.

polycaprolactone. Biodegradable thermoplastic polymer derived from the chemical synthesis of crude oil. It may have application in supporting skin-tissue growth for the purposes of skin grafts (Source: Tissue Engineering, August 2001, pages 441–455).

polyethylene glycol. Also listed as PEG on ingredient labels, polyethylene glycol is an ingredient that self-proclaimed “natural” Web sites have attempted to make notoriously evil. They gain a great deal of attention by attributing horror stories to PEG, associating it with antifreeze (however, antifreeze is ethylene glycol, not polyethylene glycol), and there is no research indicating that PEG compounds pose any problem for skin. Quite the contrary: PEGs have no known skin toxicity and can be used on skin with great results (Sources: Advanced Drug Delivery Reviews, June 2002, pages 587–606; and Cancer Research, June 2002, pages 3138–3143). The only negative research for this ingredient indicates that large quantities given orally to rats can cause tumors, but that is unrelated to topical application.

Polyethylene, when it is not combined with glycol, is the most common form of plastic used in the world. It is flexible and has a smooth, waxy feel. When ground up, the small particles are included in scrubs as a gentle abrasive. When mixed with glycol, it becomes a viscous liquid. In the minuscule amounts used in cosmetics, it helps keep products stable and performs functions similar to those of glycerin. Because polyethylene glycol can penetrate skin, it is also a vehicle that helps deliver other ingredients deeper into the skin. It is also used internally in medical procedures to flush and clean the intestinal tract. See propylene glycol.

polyglucuronic acid. See film-forming agent.

polyglycerol monostearate. Used as an emollient and thickening agent in cosmetics. See glyceryl ester.

polyglyceryl methacrylate. See film-forming agent.

polyglyceryl-3 methylglucose distearate. See glyceryl ester.

Polygonum cuspidatum root extract. Extract of the Japanese knotweed plant. When eaten it may have weak estrogenic activity (Source: Bioorganic and Medicinal Chemistry Letters, July 2001, pages 1839–1842) and antitumor activity (Source: Journal of Nutrition, June 2001, pages 1844–1849). It also has antioxidant properties (Source: Biological & Pharmaceutical Bulletin, January 1995, pages 162–166).

polyhydroxy acid. Ingredients such as gluconolactone and lactobionic acid are types of polyhydroxy acid (PHA). They are supposed to be as effective as AHAs but less irritating (NeoStrata is the company that holds a patent on glycolic acid as an antiwrinkle agent, as well as a patent for gluconolactone for reducing the appearance of wrinkles). Gluconolactone and lactobionic acid are chemically and functionally similar to AHAs. The significant difference between them and AHAs is that gluconolactone and lactobionic acid have larger molecular structures, which limits their ability to penetrate into the skin, resulting in a reduction of irritating side-effects. Supposedly, this reduced absorption into the skin does not hamper their effectiveness. Does that mean gluconolactone and lactobionic acid are better for your skin than AHAs in the form of glycolic acid or lactic acid? According to an Internet-published class lecture by Dr. Mark G. Rubin (Source: http://128.11.40.183/lasernews/rubin_lecture/21.html), a board-certified dermatologist and assistant clinical professor of dermatology at the University of California, San Diego, research on gluconolactone demonstrated only a “6% decrease in dermal penetration” in comparison to glycolic acid, which “isn’t a dramatic improvement.” Gluconolactone may be slightly less irritating for some skin types, but this isn’t the magic bullet for exfoliation that beauty magazines and some cosmetics companies have been extolling. There is no independent research information available about lactobionic acid.

polyhydroxysteatic acid. Synthetic polymer related to stearic acid. It functions as a suspending agent.

polyquaterniums. Group of ingredients used primarily in hair-care products for their antistatic and film-forming properties. They can have water-binding properties for skin due to the sheer “plastic” film layer they create on skin.

polysaccharide. Natural component of skin that can be a good water-binding agent and potentially have antioxidant properties. See mucopolysaccharide and natural moisturizing factor (NMF).

polysorbate-20. See polysorbates.

polysorbates. Fatty acids that are used as emollients and thickening agents in cosmetics. See fatty acid.

polyvinyl alcohol. See plasticizing agents.

polyvinylpyrrolidone. Usually listed on ingredient labels as PVP or PVP copolymer, it is one of the primary ingredients used in hairstyling products to hold hair in place. When present in minuscule amounts in skin-care products, it places an imperceptible film over the skin that is considered to be water-binding and that helps give the appearance of firmer skin. It can be a skin sensitizer for some individuals. See film-forming agent.

pomegranate extract. Extract that contains ellagic acid, and is considered effective as an anticarcinogen and antioxidant when taken orally. There is no research showing what effect, if any, this extract can have on skin (Sources: Journal of Agricultural Food Chemistry, January 2002, pages 81–86, and 166–171; and International Journal of Oncology, May 2002, pages 983–986).

Poria cocos extract. Also known as Hoelen and Fu ling. Extract derived from a mushroom, which has antioxidant and anti-inflammatory properties (Sources: Life Sciences, January 2002, pages 1023–1033; and Journal of Ethnopharmacology, November 2000, pages 61–69).

Porphyridium cruentum extract. Extract derived from a type of red algae. There is research showing components of red algae contain the omega-3 fatty acid eicosapentaenoic acid, the omega-6 fatty acid arachidonic acid, and other skin-friendly ingredients such as polysaccharides. Whether or not the entire red algae extract provides benefit when applied topically on skin is not known (Sources: Bioseparation, September 2000, pages 299–306; and Free Radical Biology and Medicine, February 1996, pages 241–249).

Portulaca oleracea extract. Extract that may have anti-inflammatory or analgesic properties (Sources: Journal of Ethnopharmacology, July 2001, pages 171–176, and December 2000, pages 445–451).

potassium. Important element in diet that is present in such fruits as bananas and citrus. It is also an earth mineral that has absorbent properties and some disinfecting properties, but can also be a skin irritant.

potassium ascorbyl tocopheryl phosphate. Blend of vitamins C and E with phosphorus that functions as an antioxidant. See antioxidant.

potassium cetyl phosphate. Used as a detergent cleansing agent. See surfactant.

potassium hydroxide. Also known as lye, a highly alkaline ingredient used in small amounts in cosmetics to modulate the pH of a product. It is also used as a cleansing agent in some cleansers. In higher concentrations it is a significant skin irritant.

potassium myristate. Detergent cleansing agent that is a constituent of soap; it can be drying and sensitizing for some skin types. See surfactant.

PPG-12 buteth-16. Versatile ingredient composed of several non-volatile alcohols. Functions as a skin-conditioning agent, emulsifier, solvent, and surfactant.

PPG-14 butyl ether. Used as a hair- and skin-conditioning agent.

PPG-2 myristyl ether propionate. Mixture of glycols and fatty alcohols used as a skin-conditioning agent and, in some cases, as a thickening agent.

pregnenolone acetate. Precursor to other hormones, it can affect levels of progesterone and estrogen in the body when taken orally. When applied to skin it may work as a water-binding agent. There is no information about whether absorption through the skin is possible.

preservatives. Substances used in cosmetics to prevent bacterial and microbial contamination of products. While there is definitely a risk of irritation from these types of ingredients, the risk to skin and eyes from using a contaminated product is considered by many scientists to be even greater.

progesterone USP. A study published in the American Journal of Obstetrics and Gynecology (June 1999, pages 1504–1511) states that “In order to obtain the proper (effective) serum levels with use of a progesterone cream, the cream needs to have an adequate amount of progesterone in it [at least 30 milligrams per gram]. Many over the counter creams have little [for example, 5 milligrams per ounce] or none at all. The creams that are made from Mexican yams are not metabolized to progesterone by women. The cream used in the above study (Pro-Gest) contains pure United States Pharmacopoeia [USP] progesterone.” Dr. John Lee, author and longtime proponent of topically applied progesterone, explains that “The USP progesterone used for hormone replacement comes from plant fats and oils, usually a substance called diosgenin, which is extracted from a very specific type of wild yam that grows in Mexico, or from soybeans. In the laboratory, diosgenin is chemically synthesized into real human progesterone. Some companies are trying to sell … ‘wild yam extract’ [or other plant extracts] … claiming that the body will then convert it into hormones as needed. While we know this can be done in the laboratory, there is no evidence that this conversion takes place in the human body.” Dr. Lee is quick to explain that he doesn’t sell any of these products and receives no profit from their sale. He also does not recommend the use of natural progesterone creams with any other active hormones or herbs. See Paula’s article “Progesterone” at http://www.cosmeticscop.com.

proline. See amino acid.

propolis. Brownish, resinous material that is collected by bees and used to construct the hive. It has antibacterial and anti-inflammatory properties for skin (Source: Antimicrobial Agents and Chemotherapy, May 2002, pages 1302–1309).

propylene carbonate. Liquid used as a solvent and film-forming agent. See film-forming agent.

propylene glycol. Along with other glycols and glycerol, this is a humectant or humidifying and delivery ingredient used in cosmetics. There are Web sites and spam e-mails stating that propylene glycol is really industrial antifreeze and that it is the major ingredient in brake and hydraulic fluids. These sites also state that tests show it is a strong skin irritant. They further point out that the Material Safety Data Sheet (MSDS) on propylene glycol warns users to avoid skin contact because systemically (in the body) it can cause liver abnormalities and kidney damage. As ominous as this sounds, it is so far from the reality of cosmetic formulations that almost none of it holds any water or poses real concern. It is important to realize that the MSDS sheets are talking about 100% concentrations of a substance. Even water and salt have frightening comments regarding their safety according to their MSDSs. In cosmetics, propylene glycol is used only in the smallest amounts to keep products from melting in high heat or freezing when it is cold. It also helps active ingredients penetrate the skin. In the minute amounts used in cosmetics, it is not a concern in the least. Women are not suffering from liver problems because of propylene glycol in cosmetics. And finally, according to the U.S. Department of Health and Human Services, within the Public Health Services Agency for Toxic Substances and Disease Registry, “studies have not shown these chemicals [propylene or the other glycols as used in cosmetics] to be carcinogens” (Source: http://www.atsdr.cdc.gov). See Paula’s article, “Propylene Glycol” at http://www.cosmeticscop.com.

propylene glycol stearate. Mixture of propylene glycol and stearic acid used as a skin-conditioning agent and emulsifier. S ee propylene glycol and stearic acid.

propylparaben. See parabens.

proteases. Enzymes that are part of a process that causes the breakdown of amino acids and proteins in skin (Source: http://www.chemistry-info.net/). There is research showing that proteases, when applied topically to skin, can reduce the visible scaling associated with dry, flaky skin (Source: Archives of Dermatological Research, November 2001, pages 500–507). Whether proteases can be of benefit for wound healing when applied topically is unclear (Source: Experimental Dermatology, October 2001, pages 337–348).

protein. Proteins are the fundamental components of all living cells and include a diverse range of biological substances, such as enzymes, hormones, and antibodies, that are necessary for the proper functioning of any organism, plant or animal. The human body contains perhaps 100,000 different proteins, each composed of an assortment of 20 or so amino acids. The sequence of these amino acids determines the unique properties of each protein, such as, for example, its role as an enzyme acting as a catalyst for a specific biochemical reaction. If even one of the essential amino acids is missing, the protein cannot be formed. This fact is well known to nutritionists because ensuring an adequate supply of essential amino acids is important in determining the nutritional value of proteins in the diet. Components of proteins can have varying benefits for skin, but overall they are used for their water-binding and emollient properties.

Prunella vulgaris. See self-heal.

Prunus americana. See plum extract.

Prunus domestica seed extract. See plum extract.

Prunus dulcis. See almond oil.

Pseudopterogorgia elisabethae. See sea whip extract.

Pueraria lobata. See kudzu root.

pullulan. Glucan gum produced by black yeast that contains polysaccharides, which makes it a good water-binding agent, thickening agent, and antioxidant. See beta-glucan and mucopolysaccharide.

Punica granatum extract. See pomegranate extract.

purified water. See deionized water.

PVM/MA decadiene crosspolymer. Synthetic polymer used as a film-forming and thickening agent.

PVP. See polyvinylpyrrolidone.

PVP copolymer. See polyvinylpyrrolidone.

PVP/dimethylaminoethylmethacrylate. Polymer formed from PVP (polyvinylpyrrolidone) and the film-forming agent dimethylaminomethacrylate. See film-forming agent and polyvinylpyrrolidone.

pycnogenol. Antioxidant derived from the bark of the French Maritime pine tree. The term pycnogenol was previously used generically, but is now a U.S.-registered trademark. Only one company (Horphag Research, Ltd.) has access to this ingredient, and it is patent-protected.

There is a great deal of research on pycnogenol. However, most of the research dates back to 1990 and earlier (Source: U.S. Patent No. 4,698,360 entitled “Plant Extract with a Proanthocyanidins Content as Therapeutic Agent Having Radical Scavenging Effect and Use Thereof”). Prior to and even after pycnogenol was trademarked, it was used freely as a generic term for procyanidins. Procyanidins (also known as proanthocyanidins) are pigments belonging to the flavonoid family of ingredients. In addition to being derived from pine bark, procyanidins occur naturally in grape seeds (so red wine is a good source), peanut skins, unripe strawberries, apples, and cocoa beans.

There are studies supporting the notion that pycnogenol is a potent antioxidant with strong free-radical-scavenging properties (Source: Free Radical Biology and Medicine, September 1999, pages 704–724). The most recent studies examined the effect of pycnogenol when taken as an oral supplement for various conditions, most often circulation problems (Sources: Angiology, October–November 2006, pages 569–576; and Clinical and Applied Thrombosis/Hemostasis, April 2006, pages 205–212). However, there is no research showing that it can have any effect on wrinkles (Source: Dermatologic Surgery, July 2005, pages 873–880). See antioxidant and bioflavonoid.

pyridoxine hydrochloride (HCL). Scientific name for vitamin B6; may have antibacterial and antioxidant benefits for skin when applied topically.

Pyrus cydonia. See quince seed.

Pyrus malus. Species of apple; the pectin derived from it is used as a thickener in cosmetics.