<unk>  is estimated to affect 2–4% of the population of the western world. The rate of<unk>  varies according to age, region and ethnicity; a combination of environmental and genetic factors is thought to be responsible for these differences. It can occur at any age, although it most commonly appears for the first time between the ages of 15 and 25 years. Approximately one third of people with<unk>  report being diagnosed before age 20.<unk>  affects both sexes equally.<unk>  affects about 6.7million Americans and occurs more frequently in adults.<unk>  is about five times more common in people of European descent than in people of Asian descent. People with inflammatory bowel disease such as Crohn disease or ulcerative colitis are at an increased risk of developing<unk> .<unk>  is more common in countries farther from the equator. Persons of white European ancestry are more likely to have<unk>  and the condition is relatively uncommon in African Americans and extremely uncommon in Native Americans.
Psoriasis
Onychomycosis
Parapsoriasis
Basal-cell carcinoma
Lupus vulgaris
Dermatitis
Vitiligo
Dandruff