Skin color is determined by melanin, which is produced by skin cells called melanocytes. When these cells are exposed to the sun, they produce more melanin. This results in a tan.

Melanin helps protect the skin from UV rays that can damage it. Loss of melanocytes or defective melanin production results in light patches on skin. If you’re dark-skinned, the contrast of normal skin and the light patches may be very noticeable. If you’re light-skinned, the light patches are less noticeable unless you get a tan.

You may lose melanin for many reasons and in different degrees.

• A common cause of temporary loss of skin color is infection with a fungus, called Malassezia. The condition is called tinea versicolor. It can happen anywhere, but happens most often in hot, humid climates. Scaly patches of red or brown develop that turn to white as color is lost. Treating this fungal infection will usually return normal color to skin.
• Heredity factors may play a role. Albinos, for example, have white skin because they are born without an enzyme necessary to produce melanin.
• Autoimmune problems can cause loss of color. Vitiligo, for example, is caused by damage to the melanin-producing cells by the body’s own immune cells. This results in stark-white patches on skin.
• Skin irritation or trauma may result in hypopigmentation, or slight loss of skin color. This is usually temporary until it heals.

It is important for your doctor to evaluate these white patches. He or she can determine the cause of loss of color and see if treatment is available. It is very important to protect such areas from the sun. They are more likely to burn.