Skin whitening
Skin whitening is a term covering a variety of cosmetic methods used to whiten the skin, in parts of East Asia,  the Americas, the Middle East, and Africa.
Skin lightening or whitening is a controversial topic as it is closely intertwined with the detrimental effects on health, identity, self image and racial supremacy. See article on colonial mentality.
Many skin whitening cremes are made from deadly chemicals.

# 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. This is reportedly the reason for the apparent changes in singer Michael Jackson's skin tone over the years, but has been proven that even skin whitening couldn't change the entire color of someones skin.
Some people treat larger areas to lighten the natural complexion, out of esthetic preference or to avoid social/work discrimination and gain access to better income (this is true, for  example, of prostitutes) or higher social position. This kind of colorism commonly occurs in India. 
An additional application is genital or anal bleaching, intended to reduce the typically darker pigmentation of the genital and perianal area.

# History
In Japan, geishas were (and still are) known for their painted white skin, which represents beauty, grace, and high social status.
In Iran, during the Achaemenid dynasty, farmers and civil workers used some kind of lightening lotion to keep their skin white and soft.
Today, skin whitening products are available in the form of creams, pills, soaps or lotions. The mechanism of permanent whitening is usually by the breakdown of melanin by enzymes, such as that contained in the droppings of the Japanese bush warbler or reducing agents such as Hydroquinone. Most whitening creams also contain a UV block to prevent sun damage to the skin.

# Melanin and pigmentation
Uneven pigmentation affects most people, regardless of ethnic background or skin color. Skin may either appear lighter or darker than normal; there may be blotchy, uneven areas, patches of brown to gray discoloration or freckling. Skin pigmentation disorders occur because the body produces either too much or too little melanin. Melanin is the pigment produced by melanocyte cells. It is triggered by an enzyme called tyrosinase, which creates the color of skin, eyes, and hair shades.
Melanin has two major forms that combine to create varying skin tones. Eumelanin produces a range of brown skin and hair color, while pheomelanin imparts a yellow to reddish hue.
Melanin provides some amount of sun protection for the skin by absorbing ultraviolet light. Darker skin colors are less susceptible to sunburn and the overall effects of sun damage.
Increased melanin production  also known as hyperpigmentation  is often referred to as melasma, chloasma or solar lentigenes.
- Melasma is a general term describing darkening of the skin.
- Chloasma is generally used to describe skin discolorations caused by hormones. These hormonal changes are usually the result of pregnancy, birth control pills or estrogen replacement therapy.
- Solar lentigenes is the technical term for darkened spots on the skin caused by the sun. Solar refers to sunlight and lentigene describes a darkened area of skin. These spots are quite common in adults with a long history of unprotected sun exposure.
Aside from sun exposure and hormones, hyperpigmentation can be caused by skin damage, such as remnants of blemishes, wounds or rashes. This is especially true for those with darker skin tones.
The most typical cause of darkened areas of skin, brown spots or areas of discoloration is unprotected sun exposure. Once incorrectly referred to as liver spots, these pigment problems are not connected with the liver.
On lighter to medium skin tones, solar lentigenes emerge as small- to medium-sized brown patches of freckling that can grow and accumulate over time on areas of the body that receive the most unprotected sun exposure, such as the back of the hands, forearms, chest, and face. For those with darker skin colors, these discolorations can appear as patches or areas of ashen-gray skin.

# 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. 

# Sunscreen
Sunscreen is a product used to protect the skin from ultraviolet rays, to avoid damage and/or darkening of the skin. Higher SPFs contain greater quantities of the UVA-protecting ingredients titanium dioxide, zinc oxide or avobenzone.

# Topical treatments
Topical hydroquinone is considered by many dermatologists to be a safer, similarly effective (if not more so), and less expensive option than lasers or deep peel treatments. 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 be powerful tools against sun- or hormone-induced melasma.
Some research has shown topical azelaic acid in 15% to 20% concentrations to be as efficacious as hydroquinone with a decreased risk of irritation. Tretinoin by itself has also been shown to be useful in treating hyperpigmentation of sun-damaged skin. Kojic acid, alone or in combination with glycolic acid or hydroquinone, also has shown good results due to its inhibitory action on tyrosinase (though kojic acid has had problems in terms of stability and potential negative effects on the skin and is rarely used today). Several plant extracts and vitamin C also have some research showing them to be effective for inhibiting melanin production. 

## Mercury
Many skin whiteners contain toxic mercury such as mercury(II) chloride or ammoniated mercury as the active ingredient. 

## Hydroquinone
In medical literature, hydroquinone is considered the primary topical ingredient for inhibiting melanin production. Its components have potent antioxidant abilities.
Hydroquinone is a strong inhibitor of melanin production, meaning that it prevents skin from making the substance responsible for skin color. Hydroquinone does not bleach the skin, and can only disrupt the synthesis and production of melanin hyperpigmentation. It has been banned in some 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. This is particularly true in Africa where adulterated skin lightening products are commonplace.
Because of hydroquinone's action on the skin, it can be 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.
Hydroquinone can be an unstable ingredient in cosmetic formulations. When exposed to air or sunlight it can turn a strange shade of brown. Therefore, when you are considering a hydroquinone product, it must be packaged in a non-transparent container that minimizes light and air exposure. Hydroquinone products packaged in jars are not recommended because they become ineffective shortly after opening.

## Alternatives to hydroquinone
Some of alternative lighteners are derivatives of hydroquinone. They 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-beta-D-glucoside), which can inhibit melanin production. Pure forms of arbutin are considered more potent for affecting skin lightening (alpha-arbutin, beta-arbutin, and deoxy-arbutin).
Other options with some amount of research regarding their potential skin lightening abilities are licorice extract (specifically glabridin), azelaic acid, and stabilized vitamin C (L-ascorbic acid, ascorbic acid, and magnesium ascorbyl phosphate).
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.

## Arbutin
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. Concentration protocols have yet to be established for arbutin, meaning it is not known how much arbutin it takes to lighten skin when it is added to a cosmetic formulation. Moreover, there are patents controlling its use for skin lightening. Many cosmetics companies use plant extracts that contain arbutin. There is little to no research showing the plant extract source of arbutin as having any impact on skin, especially not in the tiny amounts used in cosmetics.

## 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.

## 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. 
Like laser treatments, alpha hydroxy acid peels (using 50% concentrations or greater) may remove skin discolorations. Only a qualified physician should perform these types of facial peels.

## 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. 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 is it a good antioxidant. Further, some controversial research has suggested that kojic acid may have carcinogenic properties in large doses. www.isclinical.com/whitepapers/kojic_acid_safety.htm 

## 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 20% concentration. Azelaic acid is used to treat acne, but there also is research showing it to be effective for skin discolorations. Other research also indicates azelaic acid may be an option for inhibiting melanin production.

## Vitamin C
Magnesium ascorbyl phosphate, L-ascorbic acid, ascorbyl glucosamine, and ascorbic acid are various forms of vitamin C considered stable and effective antioxidants for skin. There are very few studies showing them to have benefit for inhibiting melanin production. The concentrations of these ingredients used in tests were generally high (more than 5%), which is rarely used in cosmetic formulations..

# 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.