Skin whitening reduces the concentration or production of melanin in the skin. Melanin is a pigment produced by cells called melanocytes. The amount of melanin in your skin is mostly determined by genetics.
People with dark skin have more melanin. Hormones, sunlight, and certain chemicals also affect melanin production.
Applying a skin whitening product to the skin it decreases the number of melanocytes in your skin. This can result in lighter skin and a more even appearance to the skin.