The exact cause of is not known. Many scientists believe that the condition may be passed down from parents to their children (inherited). About one-third of people who have psoriasis have one or more family members with the condition.1 But it is not clear that genetic factors alone determine whether you develop psoriasis. Psoriasis is not contagious-it cannot be spread by touch from person to person.
Doctors believe that the is a factor in the development of psoriasis. This is because increased numbers of white blood cells are present between the abnormal layers of skin and because psoriasis responds to drugs that suppress the immune system.
Other factors may contribute to the development of psoriasis, make the condition worse, or make it return, including:
- Climate. Cold, dry weather causes symptoms to become worse. Hot weather, sunlight, and humidity may improve symptoms.
- Skin injury. An injury to the skin can cause psoriasis patches to form anywhere on the body, including the site of the injury. This includes injuries to your nails or nearby skin while trimming your nails.
- Stress and anxiety. Stress can cause psoriasis to appear suddenly (flare) or can make symptoms worse.
- Infection. Infections such as can cause psoriasis to appear suddenly (guttate psoriasis), especially in children.
- Certain medicines.Certain medicines, such as , , and lithium, have been found to make psoriasis symptoms worse. Whenever your doctor prescribes any medicines for you, tell him or her that you have psoriasis.