Skin whitening

Skin whitening, skin lightening, and skin bleaching refer to the practice of using chemical substances in an attempt to lighten skin tone or provide an even skin complexion by reducing the melanin concentration in the skin. Several chemicals have been shown to be effective in skin whitening, while some have proven to be toxic or have questionable safety profiles, adding to the controversy surrounding their use and impacts on certain ethnic groups.

Uses

Specific zones of abnormally high pigmentation such as moles and birthmarks may be depigmented to match to the surrounding skin. Conversely, in cases of vitiligo, unaffected skin may be lightened to achieve a more uniform appearance.^[1] Long term use of skin whiteners can lead to pigmentation increasing to the joints of the fingers, toes, buttocks and ears. The skin of the face can become thinned and the area around the eyes can have increased pigmentation causing a 'bleach panda effect'.^[2]

2012 sales of skin lightening creams in India alone totaled 258 tons^[3] and the global market for skin lighteners is projected to reach US $19.8 billion by 2018 based on sales growth primarily in Asia, Africa and the Middle East.^[4]

Combination treatments

Most skin-lightening treatments, which can reduce or block some amount of melanin production, are aimed at inhibiting tyrosinase. Many treatments use a combination of topical lotions or gels containing melanin-inhibiting ingredients along with a sunscreen, and a prescription retinoid. Depending on how the skin responds to these treatments, exfoliants — either in the form of topical cosmetic or chemical peels — and lasers may be used. New development using LED systems are also showing good results.^{[5][6][7][8][9]}

There are various mechanisms described for achieving this. Inhibiting tyrosinase activity reduces the synthesis of melanin so that as existing skin cells are naturally exfoliated keratinocytes with less melanin are eventually brought to the surface, giving the skin a lighter, more even toned complexion.^[10]

Pre-melanin synthesis

Tretinoin

Research has shown that the use of tretinoin (also known as all-trans retinoic acid) can only be somewhat effective in treating skin discolorations.^{[6][11][12][13]} Users of tretinoin have to avoid sunlight, as the skin can tan. Using tretinoin always makes the skin more sensitive to UVA and UVB rays.

During melanin synthesis

Hydroquinone

In medical literature, hydroquinone is considered the primary topical ingredient for inhibiting melanin production.^{[14][15][16][17]} Its components have potent antioxidant abilities.^[18] Topical hydroquinone comes in 2% (available in cosmetics) to 4% (or more) concentrations (available from a physician or by prescription), alone or in combination with tretinoin 0.05% to 0.1%. Research has shown hydroquinone and tretinoin to prevent sun- or hormone-induced melasma.^[6]

Hydroquinone is a strong inhibitor of melanin production, meaning that it prevents dark skin from making the substance responsible for skin color.^[19] Hydroquinone does not bleach the skin but lightens it, and can only disrupt the synthesis and production of melanin hyperpigmentation. It has been banned in all European countries (e.g. France) because of fears of a cancer risk.

Some concerns about hydroquinone's safety on skin have been expressed, but the research when it comes to topical application indicates negative reactions are minor or a result of using extremely high concentrations or from other skin-lightening agents such as glucocorticoids or mercury iodine. Any perceived risk is most likely applicable for African women.^[20] Hydroquinone has been shown to cause leukemia in mice and other animals. The European Union banned it from cosmetics in 2001, but it shows up in bootleg creams in the developing world. It is sold in the United States as an over-the-counter drug, but with a concentration of hydroquinone not exceeding 2 percent.^[21]

Because of hydroquinone's action on the skin, it can be an irritant, particularly in higher concentrations of 4% or greater and predictably when combined with tretinoin. Some medications have been created that combine 4% hydroquinone with tretinoin and a form of cortisone. The cortisone is included as an anti-inflammatory. The negative side effect of repeated application of cortisone is countered by the positive effect of the tretinoin so that it does not cause thinning of skin and damage to collagen.^[22] Safer alternatives are more expensive but are available.

Arbutin

Some of alternative lighteners are derived from natural sources of hydroquinone. These include Mitracarpus scaber extract, Uva ursi (bearberry) extract, Morus bombycis (mulberry), Morus alba (white mulberry), and Broussonetia papyrifera (paper mulberry). All of these contain arbutin (technically known as hydroquinone-β-D-glucoside), which can inhibit melanin production. Pure forms of arbutin are considered more potent for affecting skin lightening.

Arbutin is derived from the leaves of bearberry, cranberry, mulberry or blueberry shrubs, and also is present in most types of pears. It can have melanin-inhibiting properties.^[23] Arbutin and other plant extracts are considered safe alternatives to commonly used depigmenting agents to make the skin fairer. Medical studies have shown the efficiency of arbutin for skin lightening.^[24] There are patents controlling its use for skin lightening. Arbutin actually exists in two isomers, alpha and beta. The alpha isomer offers higher stability over the beta isomer and is the preferred form for skin lightening indications.

Kojic acid

Kojic acid is a by-product in the fermentation process of malting rice for use in the manufacturing of sake, the Japanese rice wine. Some research shows kojic acid to be effective for inhibiting melanin production.^[25] However, kojic acid is an unstable ingredient in cosmetic formulations. Upon exposure to air or sunlight it can turn brown and lose its efficacy. Many cosmetic companies use kojic dipalmitate as an alternative because it is more stable in formulations. However, there is no research showing kojic dipalmitate to be as effective as kojic acid, although it is a good antioxidant. Further, some controversial research has suggested that kojic acid may have carcinogenic properties in large doses.^[26] Other further studies show that kojic acid is not carcinogenic, but can cause allergic contact dermatitis^[27] and skin irritation.^[28][29]

Azelaic acid

Azelaic acid is a component of grains, such as wheat, rye, and barley. It is applied topically in a cream formulation at a 10-20% concentration. Azelaic acid is used to treat acne, but there also is research showing it to be effective for skin discolorations.^[30] Other research also indicates azelaic acid may be an option for inhibiting melanin production.^[5]

Vitamin C

Vitamin C and its various forms (ascorbic acid, magnesium ascorbyl phosphate, etc.) are considered an effective antioxidant for the skin and help to lighten skin. One study^[31] found it raises glutathione levels in the body. Another study found that brownish guinea pigs given vitamin C, vitamin E and L-cysteine, simultaneously, led to lighter skin.^[32]

Glutathione

Glutathione is a tripeptide molecule found in mammalian bodies. It is an antioxidant that plays an important role in preventing oxidative damage to the skin.^[33] In addition to its many recognized biological functions, glutathione has also been associated with skin lightening ability.^[34]

Glutathione is an ingredient in some cosmetics preparations. Glutathione for skin whitening is available in cream, soap, lotion, nasal spray and injectable form. Glutathione that is applied on the skin in the form of lotion is not efficiently absorbed by the skin cells as the thiol group undergoes rapid formation of disulfide.^[35] When taken orally, glutathione is hydrolyzed by enzymes in the gastrointestinal tract resulting in reduced bioavailability.^[36] The level of glutathione increased in smalls amounts temporarily when large oral doses were administered.^[37] As a result, the effectiveness of externally administered glutathione is slowed down by its inability to cross cell membranes efficiently and its rapid degradation by enzymes in the gastrointestinal tract.^[35] On the contrary, intravenous glutathione delivers very high doses directly into the systemic circulation and is the preferred mode of administering glutathione. However, this method of administrating the antioxidant might flood the cells with glutathione that may cause reductive stress.^[38] This might expose people to potential health risks associated with long-term use of high dose of glutathione.^[39]

Glutathione can be combined with many other agents like vitamin C to increase its absorption, N-acetyl cysteine to boost its level, and other antioxidants like vitamin E. Some oral intake of glutathione could have dangerous effect when combined with other skin whitening agents such as hydroquinone which is a carcinogenic element and monobenzone which causes irreversible depigmentation.^[40]

Cinnamomum subavenium

Cinnamomum subavenium, a Chinese herb, has been suggested for use as a skin whitening agent. The plant contains substances which inhibit production of tyrosinase, an enzyme which catalyzes the production of melanin. The herb has not been established as either effective or safe but is being researched by Hui-Min Wang and his colleagues at Kaohsiung Medical University in Taiwan where experiments shown that it was effective at causing Zebrafish to lose their stripes.^[41]

Post-melanin synthesis

Alpha hydroxy acids

Alpha hydroxy acids (AHAs) — primarily in the form of lactic acid and glycolic acid — are the most researched forms of AHAs because they have a molecular size that allows effective penetration into the top layers of skin. It is generally assumed that in and of themselves AHAs in concentrations of 4% to 15% are not effective for inhibiting melanin production and will not lighten skin discolorations in that manner. It is believed that their benefit is in helping cell turnover rates and removing unhealthy or abnormal layers of superficial skin cells (exfoliation) where hyperpigmented cells can accumulate. However, other research has shown that lactic and glycolic acids can indeed inhibit melanin production separate from their actions as an exfoliant on skin.^[42]

Alpha hydroxy acid peels (using 50% concentrations or greater) may remove skin discolorations. Only a qualified physician should perform these types of facial peels.^[43]

Niacinamide

Niacinamide is claimed to be a much safer alternative when applied topically for skin or genitalia whitening. According to research by Procter & Gamble, a cosmetics company, niacinamide has no adverse side-effects. It also promotes acne reduction, increases skin moisture, and reduces fine wrinkles.^[44]

Other/ungrouped

Depigmenting agents

Most commonly, depigmentation of the skin is linked to people born with vitiligo, which produces differing areas of light and dark skin. These individuals, if they so decided to use a lightening process to even out their skin tone, could apply a topical cream containing the organic compound monobenzone to lessen the remaining pigment. Monobenzone may cause destruction of melanocytes and permanent depigmentation. An alternate method of lightening is to use the chemical mequinol over an extended period of time. Increasingly, people who are not afflicted with the vitiligo experiment with lower concentrations of monobenzone creams in the hope of lightening their skin tone evenly. However, monobenzone is not recommended for skin conditions other than vitiligo.

Mercury

Many skin whiteners contain toxic mercury such as mercury(II) chloride or ammoniated mercury as the active ingredient. However mercury has been banned in most countries for use in skin whitening (1976 in Europe, 1990 in the USA) because it accumulates on skin and it can have the opposite results in the long term. As late as January 2016, the FDA published a warning not to use a particular brand of whitener sold in the United States due to its mercury content.^[45] Some studies suggest that long-term use could cause systemic absorption that leads to tissue accumulation of the substance.^[46]

Other

Other options with some amount of research regarding their potential skin lightening abilities are licorice extract (specifically glabridin).

There is also a small amount of research showing oral supplements of pomegranate extract, ellagic acid, vitamin E, and ferulic acid can inhibit melanin production.^[47]

Laser treatments

Both ablative and nonablative lasers can have a profound effect on melasma. However, the results are not always consistent, and problems have been reported (such as hypo- or hyperpigmentation). Laser treatments of this kind are more likely to result in problems for those with darker skin tones.^[48]

Cryosurgery

Another alternative to laser treatment is cryosurgery using liquid nitrogen. Controlled destruction of skin cells causes the skin to naturally regenerate itself. Excess melanin comes to the surface and peels off in a few days. This is particularly useful in sensitive areas like the genitals where laser treatment could leave a scar. Efficacy of the treatment depends on the depth of the pigment. Freckles in any part of the body can be treated the same way.

Controversy and negative health effects

There is evidence to suggest that some types of skin-whitening products use active ingredients (such as mercurous chloride) and hydroquinone which can be harmful.^[49] Hydroquinone had been banned in Europe. However, it is now available again but only when prescribed by a medical doctor. This is also the case in many other countries, where hydroquinone can only be prescribed by a doctor for certain skin conditions.

A test of common skin lightening creams available in Nigeria showed that they caused mutations in bacteria and were possibly carcinogenic.^[50]

See also

• Depigmentation
  • Diseases
    • Vitiligo
    • Albinism
    • Hypopigmentation
  • Agents
    • Hydroquinone
    • Monobenzone
  • Anal bleaching
  • Hyperpigmentation
  • Colorism
  • Colonial mentality
  • Shadism
  • Venetian Ceruse - white lead based cosmetic worn by Elizabeth I of England.
  • Sun tanning
  • Facial
  • Racial whitening
  • Pale (skin tone)
  • Tooth bleaching
  • Whiteness in Japanese culture

References