Psoriasis (named after the Greek word psora meaning "to itch") is a chronic disease characterized by inflamed lesions covered with silvery-white scabs of dead skin. Commonly affected areas include the scalp, elbows, knees, navel, palms, ears and groin. Psoriasis is autoimmune in origin, and is not contagious (cannot be passed from one person to another). However some people with the condition suffer from social exclusion and discrimination

Around a quarter of people with psoriasis also suffer from psoriatic arthritis, which is similar to rheumatoid arthritis in its effects. It may appear for the first time at any age, although it is more likely to appear between the ages of 11 and 45.

Psoriasis disease affects approximately 3% of people globally or around 125 million people worldwide. About 150,000 to 260,000 new cases of psoriasis are diagnosed each year. The majority of psoriasis affected people experience minor localized patches, particularly on the elbows and knees, which can be treated with topical medication.

Normal skin cells mature and replace dead skin every 28-30 days. Psoriasis causes skin cells to mature in less than a week. Due to the acceleration of the replacement process, both dead and live cells accumulate on the skin surface. Because the body can't shed old skin as rapidly as new cells are rising to the surface, raised patches of dead skin develop on the arms, back, chest, elbows, legs, nails, folds between the buttocks, and scalp.

Psoriasis is fairly more common in women rather than in men. Although the disease can develop at any age, often at puberty, 10-15% of all cases are diagnosed in children under 10, and the average age at the onset of symptoms is 28. Psoriasis is most common in fair-skinned people and extremely rare in dark-skinned individuals.

There is a genetic link and it tends to run in families. About 30% of people with one first degree relative with psoriasis develop the condition. This genetic tendency appears to need to be triggered by infection; certain medicines, including ibuprofen and lithium; psychological factors, including stress; or skin trauma.

Main symptom of psoriasis disease is grey or silvery flaky patches on the skin which are red and inflamed underneath. It can occur on any part of the body although it is most commonly found on the elbows, knees, lower back and the scalp. Regardless of type, psoriasis usually causes discomfort. The skin often itches, and it may crack and bleed. In severe cases, the itching and discomfort may keep a person awake at night, and the pain can make everyday tasks difficult.

Psoriasis is considered mild if it affects less than 5% of the surface of the body; moderate, if 5-30% of the skin is involved, and severe, if the disease affects more than 30% of the body surface.