Vitiligo in some cases

Vitiligo isn't the most deadly thing that you can come down with, like other diseases though you don't want to get it. Vitiligo is the loss of skin pigmentation in patches. This disease and several others are as a result of an auto-immune attack, which actually occurs by your own body's immune system, specifically on skin melanocytes.
Vitiligo most oftenly occurs late in adulthood. The early patches that will begin to appear on skin, may continue to grow, or may remain constant in size. Often times these patches will be irritated due to their location. A simple example of this, is on your feet and ankles, where the patches are constantly in contact, with shoes, socks, sandals, etc. Often times Vitiligo will first occur as a result of stress that hits the immune system, which makes the body react in a funny way and start to eliminate skin pigment.
Unlike most diseases, Vitiligo, is not a medical problem. In can and does in most situations cause a mental problem, as socially it is different from the norm. The only real and thing that people affected with the disease have to be careful of is to protect themselves from the sun, and other uv lights. This is required because skin pigmentation acts the barrier for our body, to protect against the sun. Without this 'layer', you can only burn, never tan.
The severity of the noticeability of the patches is different among all people, and varies greatly with the natural skin color of your body. For example if naturally your sking color is quite dark, light patches are going to be much more noticeable then if your skin is a light shade to begin with.
As always it is recommended to visit a physician immediately if you suspect that you have Vitiligo. This can save you from burns, and help to protect your body, from skin damage,etc.