Triggers for psoriasis can vary from person to person and may be internal or external.

Triggers that can start or worsen psoriasis include cigarette smoking, infection (especially those involving the upper respiratory tract), injury, medications (especially those classified as antimalarial, beta-blocker, and nonsteroidal anti-inflammatory drugs), and stress.

Some people with psoriasis also report flares with changes in diet (increased consumption of alcohol, gluten, dairy, and/or sugar) as well as weather (increased exposure to dry, cold, and/or windy climate).