Psoriasis (sore-EYE-ah-sis) is a
medical condition that occurs when skin cells grow too quickly.
Faulty signals in the immune system cause new skin cells to form in
days rather than weeks. The body does not shed these excess skin
cells, so the cells pile up on the surface of the skin and lesions
What are the signs and symptoms?
The lesions vary in appearance with the type of psoriasis. There are
five types of psoriasis: Plaque, guttate, pustular, inverse, and
erythrodermic. About 80% of people living with psoriasis have plaque
(plak) psoriasis, also called “psoriasis vulgaris.” Plaque psoriasis
causes patches of thick, scaly skin that may be white, silvery, or
red. Called plaques (plax), these patches can develop anywhere on
the skin. The most common areas to find plaques are the elbows,
knees, lower back, and scalp.
Psoriasis also can affect the nails.
About 50% of people who develop psoriasis see changes in their
fingernails and/or toenails. If the nails begin to pull away from
the nail bed or develop pitting, ridges, or a yellowish-orange
color, this could be a sign of psoriatic (sore-EE-at-ic) arthritis.
Without treatment, psoriatic arthritis can progress and become
debilitating. It is important to see a dermatologist if nail changes
begin or joint pain develops. Early treatment can prevent joint
What causes psoriasis?
Psoriasis is not contagious. You cannot get psoriasis from
touching someone who has psoriasis, swimming in the same pool, or
even intimate contact. Psoriasis is much more complex.
So complex, in fact, scientists are
still studying what happens when psoriasis develops. We know that
the person’s immune system and genes play key roles. In studying the
immune system, scientists discovered that when a person has
psoriasis, the T cells (a type of white blood cell that fights
unwanted invaders such as bacteria and viruses) mistakenly trigger a
reaction in the skin cells. This is why you may hear psoriasis
referred to as a “T cell-mediated disease.”
This reaction activates a series of
events, causing new skin cells to form in days rather than weeks.
The reason T cells trigger this reaction seems to lie in our DNA.
People who develop psoriasis inherit genes that cause psoriasis.
Unlike some autoimmune conditions, it appears that many genes are
involved in psoriasis.
Scientists are still trying to identify
all of the genes involved. One of the genes that has been identified
is called PSORS1 (SORE-ESS-1). This is one of several genes that
regulates how the immune system fights infection.
Scientists also have learned that not
everyone who inherits genes for psoriasis gets psoriasis. For
psoriasis to appear, it seems that a person must inherit the “right”
mix of genes and be exposed to a trigger. Some common triggers are a
stressful life event, skin injury, and having strep throat. Many
people say that that their psoriasis first appeared after
experiencing one of these. Triggers are not universal. What triggers
psoriasis in one person may not cause psoriasis to develop in
Who gets psoriasis?
People worldwide develop psoriasis. In the United States, nearly
7.5 million people have psoriasis and about 150,000 new cases are
diagnosed each year. Studies indicate that psoriasis develops about
equally in males and females. Research also shows that Caucasians
develop psoriasis more frequently than other races. A study
conducted in the United States found the prevalence was 2.5% in
Caucasians and 1.3% in African Americans.
A family history of psoriasis seems to increase the risk of
developing psoriasis. It is important to know that a family history
of psoriasis does not guarantee that someone will develop psoriasis.
When do people get psoriasis?
Psoriasis can begin at any age, from infancy through the golden
years. There are, however, times when psoriasis is most likely to
develop. Most people first see psoriasis between 15 and 30 years of
age. About 75% develop psoriasis before they turn 40. Another common
time for psoriasis to begin is between 50 and 60 years of age.
Does psoriasis affect quality of life?
For some people, psoriasis is a nuisance. Others find that
psoriasis affects every aspect of their daily life. The
unpredictable nature of psoriasis may be the reason. Psoriasis is a
chronic (lifelong) medical condition. Some people have frequent
flare-ups that occur weekly or monthly. Others have occasional
When psoriasis flares, it can cause severe itching and pain.
Sometimes the skin cracks and bleeds. When trying to sleep, cracking
and bleeding skin can wake a person frequently and cause sleep
deprivation. A lack of sleep can make it difficult to focus at
school or work. Sometimes a flare-up requires a visit to a
dermatologist for additional treatment. Time must be taken from
school or work to visit the doctor and get treatment.
These cycles of flare-ups and remissions often lead to feelings of
sadness, despair, guilt and anger as well as low self-esteem.
Depression is higher in people who have psoriasis than in the
general population. Feelings of embarrassment also are common.
Knowledge is power
As psoriasis is a life-long condition, it is important to take
an active role in managing it. Learning more about psoriasis, seeing
a dermatologist to discuss treatment options, and developing a
healthy lifestyle can help people live life to the fullest.
Callis Duffin K, Wong B, Horn EJ et al. “Psoriatic arthritis
is a strong predictor of sleep interference in patients with
psoriasis.” Journal of the American Academy of Dermatology
2009; 60: 604-8.
Gelfand JM, Stern RS, Nijsten T et al. “The prevalence of
psoriasis in African Americans: results from a population-based
study.” Journal of the American Academy of Dermatology 2005;
Gudjonsson JE and Elder JT. “Psoriasis.” In: Wolff, K, Goldsmith LA,
Katz SI, et al. (editors) Fitzpatrick’s Dermatology in General
Medicine. 7th ed. New York: McGraw Hill Medical;
2008. p. 169-93.
Nair RP, Stuart PE, Nistor I et al. “Sequence and haplotype
analysis supports HLA-C as the psoriasis susceptibility 1 gene.”
American Journal of Human Genetics 2006; 78: 827-51.
Society for Investigative Dermatology and American Academy of
Dermatology. “Burden of Skin Diseases.” 2004. Last accessed June 5,
2009. Available at
All content solely
developed by the American Academy of Dermatology
For an overview, visit
the AAD pamphlet
Psoriasis and Psoriatic Arthritis.
This woman has plaque
psoriasis, the most common type of psoriasis.
(Photos used with permission of the American Academy of
Dermatology National Library of Dermatologic Teaching