In about one-third of the cases, psoriasis is inherited. Researchers are studying large families affected by psoriasis to identify a gene or genes that cause the disease. People with psoriasis may notice that there are times when their skin worsens, then improves. Conditions that may cause flareups include changes in climate, infections, stress, and dry skin. Also, certain medicines, most notably beta-blockers, which are used to treat high blood pressure, and lithium or drugs used to treat depression, may trigger an outbreak or worsen the disease.
Doctors usually diagnose psoriasis after a careful examination of the skin.
However, diagnosis may be difficult because psoriasis can look like other skin diseases. There are several forms of psoriasis. In plaque psoriasis, lesions have a reddened base covered by silvery scales. Blisters of noninfectious pus appear on the skin. Attacks of pustular psoriasis may be triggered by medications, infections, emotional stress, or exposure to certain chemicals.