Hamamelis virginiana. See witch hazel.

hamamelitannin. Tannin that is found in witch hazel. It can be a skin irritant, but it also has potent antioxidant properties. See tannin.

Haslea ostrearia extract. Extract derived from a water plant also known as blue algae. In pure concentrations this extract can have antiviral properties on skin. See algae.

hawthorn extract. Extract that when taken orally may improve circulation (Source: Phytomedicine, 1994, volume 1, pages 17–24). The bioflavonoids in hawthorn are potent antioxidants. (Source: Planta Medica, 1994, volume 60, pages 323–328), but there is no research showing that this extract has any benefit for skin.

hayflower extract. Plant extract that, due to its constricting effect on skin, can be an irritant. There is no research supporting the claim that it has any effect on skin.

hazelnut oil. Oil extracted from the hazelnut and that is used as an emollient. See natural moisturizing factor (NMF).

heavy water. Water in which hydrogen atoms have been replaced by deuterium; it is used chiefly as a coolant in nuclear reactors.

Hedera helix. See English ivy extract.

hedione. Synthetic fragrant component in products, which also can be a skin irritant.

helianthus oil. See sunflower oil.

hemp seed oil. From the hemp plant, Cannabis sativa. Because both hemp and marijuana are from the genus Cannabis, they are often thought (erroneously) to have similar properties. However, because hemp contains virtually no THC (delta-9-tetrahydrocannabinol), the active ingredient in marijuana, it is not used as a drug of any kind. In cosmetics, hemp seed oil is used as an emollient. Other claims about its effect on skin are not substantiated. See fatty acid.

hepatocyte growth factor (HGF). Stimulates division in cells lining the liver, skin cells, and cells that produce skin color. See human growth factor.

hesperidin. Flavonoid found in various plants such as citrus and evening primrose oil. It has potential as a potent antioxidant—reducing the effects of sun damage and preventing some cancers. It is also taken orally to improve circulation and to strengthen capillaries. There is no published research showing it combats cellulite (Sources: Photochemistry and Photobiology, September 2003, pages 256–261; Phytotherapy Research, December 2001, pages 655–669; and Anticancer Research, July-August 1999, pages 3237–3241).

hesperidin methyl chalcone. Citrus bioflavonoid often seen in products claiming to banish dark undereye circles. There is research supporting its internal use as an aid to venous (vein) problems. One study documented that it lowers the filtration rate of capillaries, and less blood flowing though capillaries close to the surface of the skin potentially means that less hemoglobin would be oxygenated to cause the dark bluish discoloration under the eyes. However, there is no substantiated research proving that it will have this effect when this ingredient is applied topically.

Another study detailed this ingredient’s use when combined with the root of the Ruscus aculeatus plant and vitamin C, but again it was about oral consumption for alleviating symptoms of varicose veins and helping prevent them from becoming a chronic disease (Source: International Angiology, September 2003, pages 250–262). It is clear from published research that hesperidin methyl chalcone does have various benefits for the body, but diminishing severe dark circles via topical application is not one of them (Source: http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/hes_0295.shtml).

hexyl laurate. Skin-conditioning agent and emollient that is a mixture of hexyl alcohol and lauric acid.

hexylene glycol. See propylene glycol.

Himanthalia elongate extract. Extract of a species of algae. See algae.

Hippophae rhamnoides. See sea buckthorn.

histidine. See amino acid.

hoelen. A mushroom that grows underground on the roots of pines and other trees around the world. It has antibacterial, preservative, wound-healing, and water-binding properties when applied topically (Sources: BioMed Central (BMC) Complementary and Alternative Medicine, 2001, volume 1, issue 1, page 2; and Burns, March 1998, pages 157–161).

hops. There is no research showing that hops have any benefit for skin. However, components in hops may have antioxidant and antibacterial properties. The plant may also have estrogenic properties.

Hordeum vulgare extract. See barley extract.

horse chestnut extract. May have anti-inflammatory properties for skin. Orally it has been shown to reduce edema in the lower leg by improving the elastic tissue surrounding the vein (Sources: Pharmacological Research, September 2001, pages 183–193; Phytotherapy Research, March 2002, number S1, pages 1–5; and American Journal of Clinical Dermatology, 2002, volume 3, number 5, pages 341–348). See escin.

horse elder. See elecampane.

horseradish. Plant that can irritate skin and should never be applied to abraded skin.

horsetail extract. Plant extract that has a high tannin, alkaloid, and nicotine content, which can have skin-constricting properties and be irritating to skin (Source: http://www.herbmed.org). It also has antioxidant properties, but there are many other potent antioxidants that can be used that do not cause skin irritation.

Huang qi. See milk vetch root.

human growth factor. The topic of human growth factor (HGF) is exceedingly complicated. The physiological intricacies of the varying HGFs and their actions challenge any layperson’s comprehension. Nonetheless, because the use of HGF seems to be the direction some skin-care companies are taking, and because there is a large body of research showing its efficacy for wound healing (but not for wrinkles), it does deserve comment.

HGFs make up a complex family of hormones that are produced by the body to control cell growth and cell division in skin, blood, bone, and nerve tissue. Most significantly, HGFs regulate the division and reproduction of cells, and they also can influence the growth rate of some cancers. HGFs occur naturally in the body, but they also are synthesized and used in medicine for a range of applications, including wound healing and immune-system stimulation. HGFs are chemical messages that bind to receptor sites on the cell surface (receptor sites are places where cells communicate with a substance to let them know what or what not to do). HGFs must communicate with cells to instruct them to activate the production of new cells, or to instruct a cell to create new cells that have different functions. Another way to think of HGFs is that they are messengers designed to be received or “heard” by specific receptor sites or “ears” on the cell. HGFs, such as transforming growth factor (TGF, stimulates collagen production) or epidermal growth factor (EGF, stimulates skin-cell production), play a significant role in healing surgical wounds. The main task of HGFs is to cause cell division, which is helpful; however, at certain concentrations and over certain durations of application they can cause cells to over-proliferate, which can cause cancer or other health problems.

But what happens when you put HGFs on skin, particularly TGF and EGF, which some companies claim their products contain? The risk is that they could accelerate the growth of skin cancer by stimulating the overproduction of skin cells. In the case of TGF, which stimulates collagen production, it can encourage scarring, because scars are the result of excessive collagen production, and if you make too much collagen you get a scar or a knot on the skin such as a keloidal scar. Most of the research on the issue of HGFs for skin has looked primarily at the issue of wound healing, and at short-term use of HGFs. In skin-care products, however, they would be used repeatedly, and possibly over long periods of time. A shortcoming of HGFs, according to an article by Dr. Donald R. Owen in Global Cosmetic Industry (March 1999), is that “The body produces these [HGFs] in exquisitely small concentrations at just the right location and time .... Actual growth factors such as [EGF and TGF-B] are [large] configurations, which do not penetrate the skin .... They [also] lose their activity within days in water or even as solids at normal temperatures .... [Yet], even after all these complications, the siren’s song is too strong. We [the cosmetics chemists] will use them.”

(Sources: Journal of Burn Care and Rehabilitation, March–April 2002, pages 116–125; Journal of Dermatologic Surgery and Oncology, July 1992, pages 604–606; Journal of Anatomy, July 2005, pages 67–78; International Wound Journal, June 2006, pages 123–130;Tissue Engineering, January 2007, pages 21–28; Wounds, 2001, volume 13, number 2, pages 53–58; Plastic and Reconstructive Surgery, August 1995, pages 251–254, and September 1997, pages 657–664; Skin Pharmacology and Applied Skin Physiology, January–April 1999, pages 79–84; and Journal of Surgical Research, April 2002, pages 175–182).

The research into HGFs is without question intriguing, but much remains unknown at this time, especially in terms of long-term risk or stability when they are used in cosmetics and applied to skin. In this arena, if cosmetics companies continue to use HGFs, it is the consumer who will be the guinea pig.

humectant. See water-binding agent.

Humulus lupulus extract. See hops.

hyaluronic acid. Component of skin tissue that is used in skin-care products as a good water-binding agent. See natural moisturizing factor (NMF).

Hydnocarpus anthelmintica. See chaulmoogra oil.

Hydrastis canadenis. See goldenseal.

hydrocortisone. Hormone from the adrenal gland that can also be created synthetically. It has potent anti-inflammatory properties for skin, but prolonged use can destroy collagen in the skin and cause skin fragility (Sources: American Academy of Dermatology Guidelines of Care for the Use of Topical Glucocorticosteroids, http://www.aadassociation.org/Guidelines/topicalglu.html; Journal of the American Academy of Dermatology, 1996, volume 35, pages 615–619; and Cosmetic Dermatology, July 2002, pages 59–62).

hydrocotyl extract. See Centella asiatica.

hydrogen peroxide. There is a great deal of current research showing that hydrogen peroxide is problematic as a topical disinfectant because it can greatly reduce the production of healthy new skin cells (Source: Plastic and Reconstructive Surgery, September 2001, pages 675–687). Hydrogen peroxide is also a strong oxidizing agent, meaning that it generates free-radical damage. While it can function as a disinfectant, the cumulative problems that can stem from impacting the skin with a substance that is known to generate free-radical damage, impair the skin’s healing process, cause cellular destruction, and reduce optimal cell functioning are serious enough that it is better to avoid its use (Sources: Carcinogenesis, March 2002, pages 469–475; Anticancer Research, July–August 2001, pages 2719–2724; and Cellular and Molecular Biology, April 2007, pages 1–2). See free-radical damage.

hydrogenated coco-glyceride. Used as an emollient and thickening agent in cosmetics. See glyceryl ester.

hydrogenated didecene. Skin-conditioning agent derived from didecene, which is a hydrocarbon. Hydrocarbons are organic compounds that contain only carbon and hydrogen. Examples of common hydrocarbons include mineral oil, petroleum, and paraffin wax.

hydrogenated lecithin. See lecithin.

hydrogenated palm glyceride. Used as an emollient and thickening agent in cosmetics. See glyceryl ester.

hydrogenated polydecene. Synthetic polymer that functions as an emollient and skin-conditioning agent.

hydrogenated polyisobutene. Synthetic polymer used as a skin-conditioning agent and emollient.

hydrolyzed jojoba esters. Essential fatty acids from the jojoba plant, broken down by water to form a new complex with properties different from the original source. An analogy of this process is the manner in which humans digest food to turn it into energy. Jojoba esters function as skin-conditioning agents.

hydrolyzed silk. See silk.

hydrolyzed vegetable protein. Composed of various protein substances derived from vegetables and broken down by water to form a new complex with properties different from the original source. Used as a water-binding agent.

hydroquinone. Strong inhibitor of melanin production that has long been established as the most effective ingredient for reducing and potentially eliminating melasma (Source: Journal of Dermatological Science, August, 2001, Supplemental, pages 68–75), meaning that it prevents skin from making the substance responsible for skin color. Hydroquinone does not bleach the skin, which is why “bleaching agent” is a misnomer; it can’t remove pigment from the skin cell. Over-the-counter hydroquinone products can contain 0.5% to 2% concentrations of hydroquinone; 4% (and sometimes higher) concentrations are available only from physicians.

In medical literature, hydroquinone is considered the primary topical ingredient for inhibiting melanin production. Using it in combination with some other ingredients—especially tretinoin—can greatly reduce and even eliminate skin discolorations (Sources: Cutis, March 2006, pages 177–184; Journal of Drugs in Dermatology, September–October 2005, pages 592–597; Journal of Cosmetic Science, May–June 1998, pages 208–290; and Dermatological Surgery, May 1996, pages 443–447). Interestingly, hydroquinone also is a potent antioxidant (Source: Journal of Natural Products, November 2002, pages 1605–1611).

Some concerns about hydroquinone’s safety on skin have been expressed, but the research when it comes to topical application indicates that negative reactions are minor, are a result of using extremely high concentrations, or result from the use of other skin-lightening agents such as glucocorticoids or mercury iodine. This is particularly true in Africa, where adulterated skin-lightening products are commonplace (Sources: British Journal of Dermatology, March 2003, pages 493–500; and Critical Reviews in Toxicology, May 1999, pages 283–330).

According to Howard I. Maibach, M.D., professor of dermatology at the University of California School of Medicine, San Francisco, “Overall, adverse events reported with the use of hydroquinone ... have been relatively few and minor in nature.... To date there is no evidence of adverse systemic reactions following the use of hydroquinone, and it has been around for over 30 years in skin-care products.” Maibach also stated that “hydroquinone is undoubtedly the most active and safest skin-depigmenting substance....” Research supporting Maibach’s contentions was published in the Journal of Toxicology and Environmental Health (1998, pages 301–317). Concern about hydroquinone having carcinogenic properties is mostly related to industrial-grade materials and uses. For cosmetic use there appears to be no similar evidence.

Despite hydroquinone’s impressive track record and efficacy, the FDA, in September 2006, recommended that products containing hydroquinone be sold only with a prescription due to their opinion that it posed certain health risks. The FDA asserts there are animal studies showing it may be a possible carcinogen, and studies from Africa showing there is a risk of a skin disorder called ochronosis (Source: http://www.fda.gov/OHRMS/DOCKETS/98fr/E6-14263.htm).

However, there is abundant research from reputable sources that shows hydroquinone to be safe and extremely effective (Sources: Cutis, August 2006, Supplemental, pages 6–19; Journal of Cosmetic Laser Therapy, September 2006, pages 121–127; American Journal of Clinical Dermatology, July 2006, pages 223–230; and Journal of the American Academy of Dermatology, May 2006, Supplemental, pages 272–281). Surprisingly, there is even research showing that workers who handle pure hydroquinone actually have lower incidences of cancer than the population as a whole (Source: Critical Reviews in Toxicology, May 1999, pages 283–330).

Hydroquinone can be an unstable ingredient in cosmetic formulations. When exposed to air or sunlight, it oxidizes and will turn brown. Therefore, when you are considering buying and using a hydroquinone product, make sure that it is packaged in a non-transparent container that does not let in light and that minimizes exposure to air. Hydroquinone products packaged in jars are not recommended because they become ineffective shortly after opening.

For continued and increased effectiveness, hydroquinone must be used long term. Unprotected sun exposure should be avoided, because it reverses the effect of hydroquinone by increasing melanin production. Occasionally, at higher concentrations, persons with darker skin will experience increased pigmentation, but this is rare. It also can cause mild skin irritation and there is the possibility of an allergic reaction. Hydroquinone in 1% to 2% concentrations is available in over-the-counter products; 4% concentrations are available by prescription only (Source: American Journal of Clinical Dermatology, September–October 2000, pages 261–268).

hydroxyethylcellulose. Plant-derived thickening agent typically used as a binding agent or emulsifier. Also used (most often in styling products) as a film-forming agent.

hydroxylated lecithin. See lecithin.

hydroxyproline. Derived from the amino acid proline, hydroxyproline is a fundamental component of collagen and other structural proteins. Skin’s ability to heal is partly determined by the presence of hydroxyproline within it. Whether topical application of hydroxyproline to the skin can help with wound healing has not been substantiated. However, it does have water-binding properties similar to those of collagen.

hydroxypropyl guar. See guar gum.

Hypericum extract. See St. John’s wort.

hypoallergenic. Term used by the cosmetics industry to lead consumers to believe they are using a product that will not cause them to have an allergic or sensitizing skin reaction to a product. However, the word hypoallergenic is not regulated in any manner by the FDA and therefore it is used indiscriminately by cosmetics companies without any substantiation or need to show proof of the claim.

hyssop. Fragrant plant extract that may have some antibacterial properties (Source: International Journal of Food Microbiology, August 2001, pages 187–195). It may also be a skin irritant.