The exact cause of
psoriasis 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.9 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
immune system 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,
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.