Psoriasis (pronounced /sɵˈraɪ.əsɨs/; from Greek ψωρίασις,
meaning "itching condition" or "being itchy",[1] psora "itch"
+ -sis "action, condition"; also termed psoriasis
vulgaris),[2] is
a common, chronic immune-mediated skin
disease which may also affect the joints.[2]
Psoriasis is characterized by scaly, reddened patches, papules, and plaques which are usually itchy.[2] There
are five main types of psoriasis: plaque, guttate, inverse, pustular, and
erythrodermic.[3]
The
most common form, plaque psoriasis, is commonly seen as red and white hues of
scaly patches appearing on the top layer of the
skin. In plaque psoriasis, skin rapidly accumulates at these sites, which
gives it a silvery-white appearance. Plaques frequently occur on the skin of
the elbows and knees, but can affect
any area, including the scalp, palms of hands and soles of feet, and genitals.
In contrast to eczema,
psoriasis is more likely to be found on theouter side of
the joint. Fingernails and toenails are frequently
affected (psoriatic nail dystrophy) and can be seen as an isolated sign.
Psoriasis can also cause inflammation of
the joints, which is known as psoriatic arthritis. Up to 30% of individuals
with psoriasis also have psoriatic arthritis.[4]
The causes of psoriasis are not fully understood. It is
generally considered a genetic
disease which can be triggered or influenced by environmental factors.[2] Local
psoriatic changes can be triggered by an injury to the skin known as the Koebner phenomenon.[5]Various
environmental factors have been suggested as aggravating to psoriasis,
including oxidative stress,[6] stress,
withdrawal of systemic corticosteroid,
as well as other environmental factors, but few have shown statistical
significance.[7] Psoriasis
occurs when the immune system mistakes a normal skin cell for a pathogen, and
sends out faulty signals that cause overproduction of new skin cells. It is not
contagious.[8]
There is no cure,[8] but
various treatments can help to control the symptoms.[9][10] There
are many treatments available, but because of its chronic recurrent nature,
psoriasis is a challenge to treat. Withdrawal of corticosteroids (topical
steroid cream) can aggravate the condition due to the 'rebound
effect' of corticosteroids.[11]
The disorder is a chronic, recurring condition that varies
in severity from minor localized patches to complete body coverage. It occurs
in 1–3% of the general population
