Psoriasis is an inflammatory disease of the skin. It is generally characterized by the appearance of thick patches of skin that peel off. This chronic disease evolves in cycles, with periods of remission in between. It is not contagious and can be well controlled by treatment.

Psoriasis can be very unpleasant or even painful when it occurs on the palms of the hands, soles of the feet or in the folds of the skin. The extent of the disease varies greatly from person to person. Depending on where the plates are located and their extent, psoriasis can be embarrassing and affect self-esteem.

About 2% to 4% of the Western population is affected. Psoriasis is most common in Caucasians. The disease usually appears in adulthood, late twenties or early thirties. However, it can affect children, sometimes even before the age of 2.

The precise cause of psoriasis is unknown. Several factors are involved in the onset of disease, particularly genetic and environmental factors. Thus, there is often a family history of psoriasis in a third of cases. Physical stress (infection, injury, surgery, drugs) or mental stress (nervous exhaustion, anxiety, etc) can contribute to the onset of psoriasis.

Psoriasis may also be caused by autoimmune reactions occurring in the skin. These reactions stimulate the proliferation of epidermal cells. In people with psoriasis, these cells are renewed at a rate much too fast- every 3 to 6 days instead of every 28 or 30 days. Since the life of skin cells is the same, they accumulate and form thick crusts.

The most common form is plaque psoriasis, also known as psoriasis vulgaris (because it represents over 80% of cases). Other forms are guttate psoriasis, erythrodermic psoriasis and pustular psoriasis.

Psoriasis usually presents in the following regions:

·Psoriasis of the scalp, very common;

·Palmoplantar psoriasis, which affects the palms and soles of the feet;

·Inverse psoriasis, characterized by patches in skin folds

·Psoriasis of the nails (or nail).

In nearly 7% of people, psoriasis is accompanied by joint pain with swelling and stiffness, which is called psoriatic arthritis.

The disease progresses in spurts rather unpredictable and highly variable among individuals. The symptoms usually last 3 to 4 months, and may then disappear for months or years and then reappear in most cases.

It seems that people with psoriasis are more likely to suffer more from cardiovascular disorders, metabolic syndrome and obesity, for yet unknown reasons.

A reaction to medication, including lithium prescribed to treat bipolar disorder, beta-blockers against hypertension and drugs against malaria can cause psoriasis. Other risk factors for psoriasis include:

·A high level of stress.

·A scratch, a cut or insect bite.

·A sunburn.

·Cold and dry climates.

·Exposure to chemicals.

·The consumption of alcohol.

·Smoking. It aggravates the symptoms and would be a risk factor for this disease.

·Infection of the throat or respiratory tract (in the case of guttate psoriasis).