To get fair, you slowly exfoliate off the darkened skin over time and prevent the new skin from darkening.

There are several things commonly used to lighten the skin.

Hydroquinone is one of them but in higher concentrations, it can cause irritations and may even be carcinogenic. It makes skin lighter by preventing melanin from being formed.

Alchemilla a plant popular amongst the alchemists in the Middle Ages, slows the release of melanin pigments to your skin, hence slowing down the darkening of your skin.

Kojic acid is used to to prevent melanin formation.

Black-Out Yeast Complex, a formula by clinique, used extensively in its Derma White range breaks down the melanin clusters so that these can be disposed of via exfoliation and defuses irritants that would otherwise darken the skin, through its delivery of antioxidants. Most importantly, it prevents more melanin from forming by blocking away the signals to produce melanin. Read full article

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