There can be more than one cause. You should get a diagnose from a doctor to be sure.
Most common cause is a skin condition known as vitiligo. It is a very common in the U.S, and about 1% of people have it. Most likely cause of vitiligo is an autoimmune problem where your body attacks melanocytes which produce pigment. It is also suspected to be related to stress or sunrays. Vitiligo is not lethal in any way. The white patches could cover a person's body anywhere. It is physically pain-free. Extensive pigment loss can be very hard mentally.
There are a few things that might help the recovery, such as eating healthy. An enzyme, serrapeptase, might also help. There are some ultraviolet treatments and medicines, but they are mostly experimental.
Most important thing is to use sunblock in the areas without pigment. You can also add tan loation to hide the white areas from people.
If you are very careless
Pigment or pigments.
The loss of pigmentation in the skin is called Hypo-pigmentation and the total loss of skin pigment is called Albinism.
Kearns-Sayre syndrome causes ophthalmoplegia along with loss of pigment in the retina, the light-sensitive membrane lining the eye
Albinism's effects vary with its severity, with outcomes ranging from combined pigment loss in the hair, skin and iris to pigment loss limited to the retina.
Melanin
the pigment in your skin
Anthocyanin is the pigment that give blue and red potatoes their color. The pigment ranges in color from red to purple to blue.
Xanthophyll
anthocyanins
melanin
Vitiligo (also known as leucoderma), is caused by a loss of pigment in the skin, due to destruction of pigment-forming cells. This disease causes a problem with the pigment cells and can occur on any skin colour, race or gender. It is characterised by pinky white blotches which appear randomly on the body and is sensitive to light. The exact cause is unknown.
Disorders like the inability to metabolize iron and similar disorders may cause pigment cirrhosis