Psoriasis is a chronic, non-contagious skin condition characterised by areas/lesions of skin which are inflamed and scaly. Severity can range from lesions on the elbows alone to extensive body and scalp coverage. The appearance of the lesions can differ between individuals, and in the same individual lesions occurring on different parts of the body can look different in appearance.
Different Types of Psoriasis
Dermatologists describe different forms of psoriasis. The most common form is chronic plaque psoriasis, where the lesions are typically round in shape, a few centimetres in diameter, raised and covered in a silvery scale. In chronic plaque psoriasis the most common areas of the body to be affected include the scalp, knees, elbows, navel and genitals. However, plaques can occur on any area of the body for example in the ears, on the eyelids, on the palms of hands and the soles of the feet.
Other forms of psoriasis include guttate psoriasis, in which the lesions are small, drop-like, and often extensive, and pustular psoriasis, in which the lesions are characterised by pustules. Erythrodermic psoriasis is a more rare form of the condition in which the whole body is affected by erythroderma (reddening of the skin) and scaling. Erythrodermic psoriasis can lead to mortality if left untreated.
In addition to the lesions, fingernails and toenails may be affected by pitting, discolouration and separation from the nail bed. Furthermore, 1 in 20 psoriasis sufferers also have psoriatic arthritis of the joints. Psoriasis is also characterised by the Koebner phenomenon. This is the phenomenon of lesions occurring where there has been skin trauma or injury, such as a cut, an injection site or burn.
The severity of psoriasis is rarely static. Individuals are likely to cycle between differing levels of severity throughout their lifetime. Many individuals with psoriasis experience ‘spontaneous’ remissions and flare-ups through-out the course of their condition.
What causes psoriasis?
The physiological mechanisms are complex and include an acceleration of the normal process of skin renewal in certain patches. In an average individual, epidermal turnover takes 27 days, but in lesions of psoriasis this process takes only 4 days. This accelerated renewal is accompanied by alterations in the shape of the blood capillaries and increased delivery of blood to the skin surface. These changes result in the red, scaly patches of skin.
The pathogenesis of psoriasis is not known. It is thought to have a hereditary element with approximately 30% of people with psoriasis having a family member also with psoriasis. There is also some evidence of immune system involvement with activated T lymphocytes playing an important role.
How many people have psoriasis?
Studies have estimated that between 1% and 2% of the UK population have psoriasis and men and women are affected equally (Kreuger et al., 1994). Whilst the mean age of onset is 30 years, there are two main periods of onset; between the ages of 16 and 22 years, and between the ages of 57 and 60 years. There is some evidence that females are affected at an earlier age than males. Psoriasis is the third most common reason for dermatology appointments.