The skin changes that characterize psoriasis are due to the rapid turnover of cells in the epidermis. New cells are produced, grow to maturity and die too quickly, severely reducing the cell cycle. Although the cause of this is not known, it is believed to involve a faulty response of the immune system.

There is a genetic factor involved in the development of psoriasis. The disease is seen more commonly in families and, according to the National Institutes of Health, there is a family history of psoriasis in about one-third of all psoriasis patients.

The onset of psoriasis is believed to require a trigger. Triggers may also lead to flares and exacerbations. Common triggers include:

• Skin injury, including cuts, bites, bruises, burns, chafing or sunburns
  
  
• Emotional stress
  
  
• Viral or bacterial infection (e.g., thrush, HIV, strep throat)
  
  
• Certain drugs, including antimalarial drugs, beta blockers (used to treat high blood pressure), lithium, and the prolonged use of steroids
  
  
• Climate, including lack of sunlight and dry weather conditions
  
  
• Obesity
  
  
• Hormonal factors, including hypocalcemia (not enough calcium in the blood) and those involved in pregnancy
  
  
• Alcohol and smoking

Psoriasis triggers will vary from patient to patient. What triggers psoriasis in one person may not cause symptoms in another.