Researchers have been unable to identify a singular cause for psoriasis, but studies suggest psoriasis is an autoimmune disease—it begins in the immune system, the result of your immune system’s overreaction to stimuli. 

In a properly-functioning immune system, T-cells, a kind of white blood cell, protect the body against infection and disease by identifying and destroying foreign material. With psoriasis, T-cells overreact, mistaking healthy skin cells for dangerous ones, and set off a chain of unneeded immune system responses.

Certain factors may trigger psoriasis in a person who has never had symptoms before. And for those who have psoriasis, these same factors can trigger another bout with the disease.

Triggers include:

  • bacterial or viral infections, such as strep throat or the common cold
  • diseases that weaken your immune system, such as AIDS or cancer
  • emotional stress
  • dry air or dry skin (particularly from changes in weather)
  • some medicines, such as beta-blockers, lithium, and anti-malaria drugs
  • cuts, bites, or burns on the skin
  • too little sunlight or too much (sunburn)
  • increased alcohol intake
  • smoking