Psoriasis is a common and chronic skin disorder. Plaque psoriasis is the most common type of psoriasis and is characterized by red skin covered with silvery scales andinflammation. Patches of circular to oval shaped red plaques that itch or burn are typical of plaquepsoriasis. The patches are usually found on the arms, legs, trunk, or scalp but may be found on any part of the skin. The most typical areas are the knees and elbows.
Factors such as smoking, sun exposure, alcoholism, and HIV infection may affect how often the psoriasis occurs and how long the flares up last.
Approximately 1-2% of people in the United States, or about 5.5 million, have plaque psoriasis. Up to 30% of people with plaque psoriasis also have psoriatic arthritis. Individuals with psoriatic arthritis have inflammation in their joints and may have other arthritis symptoms.
Sometimes plaque psoriasis can evolve into more severe disease, such as pustular psoriasisor erythrodermic psoriasis. In pustular psoriasis, the red areas on the skin contain blisters with pus. In erythrodermic psoriasis, a wide area of red and scaling skin is typical, and it may be itchy and painful.
Psoriasis affects children and adults. Men and woman are affected equally. Females develop plaque psoriasis earlier than males. The first peak occurrence of plaque psoriasis is in people aged 16-22 years. The second peak is in people aged 57-60 years.
Psoriasis can affect all races. Studies have shown that more people in western European and Scandinavian populations have psoriasis than those in other population groups.
An individual with plaque psoriasis usually has patches of red, raised, scaly areas on the skin that may itch or burn. The patches are usually found on the knees, elbows, trunk, or scalp. Approximately, 9 out of 10 people with psoriasis have plaque psoriasis.
The flare-ups can last for weeks or months. The psoriasis goes away for a time and then returns (chronic).
General characteristics of the scaly skin of the most common type of psoriasis are as follows:
- Plaques: The plaque areas on the skin are elevated. The plaque areas vary in size (1 to several centimeters) and may range from a few to many at any given time on the skin. The shape of the plaque is usually oval but can be irregular in shape. Smaller plaque areas may merge with other areas and form a large affected area. The skin in these areas, especially when over joints or on the palms or feet, can split and bleed.
- Plaques sometimes have an area around them that looks like a halo or ring (Ring of Woronoff).
- Red color: The color of the affected skin is very distinctive. The rich, full red color is salmon colored. Sometimes the skin can have a blue tint when the psoriasis is on the legs.
- Scale: The scales are dry, thin, and silvery-white. The thickness of the scales may vary. When the scale is removed, the skin underneath looks smooth, red, and glossy. This shiny skin usually has small areas that bleed (Auspitz sign).
- Symmetry: Psoriatic plaques tend to appear on both sides of the body in the same places. For example, the psoriasis is usually on both knees or both elbows at the same time.
Other general symptoms of psoriasis are as follows:
- Scalp: The scalp can have dry, scaly skin or crusted plaque areas. Sometimes psoriasis of the scalp is confused with seborrheic dermatitis. In seborrheic psoriasis, the scales are greasy looking, not dry.
- Nails: Nail changes are commonly observed in those with plaque psoriasis. The nails may have small indentations, ridges, or pits in them. The nails can be discolored or separate from the nail bed (see Nail Psoriasis.)
- Droplets on skin: Sometimes, the skin is red and looks like it has little drops on it. This may be guttate psoriasis.
- Pus on patches: Sometimes, the patches of dry, scaly skin can crack and have pus on top of them. This may be pustular psoriasis (see Types of Psoriasis - Pustular).
- Psoriasis in children: Plaque psoriasis looks slightly different in children compared to adults. In children, the plaques are not as thick, and the affected skin is less scaly. Psoriasis may often appear in the diaper region in infancy and in flexural areas in children. The disease more commonly affects the face in children as compared to adults.
- Other areas: Although the most common body areas affected are the arms,leg, back, and scalp, psoriasis can be found on any body part. Psoriasis can be found on the genitals or buttocks, under the breasts, or under the arms. These areas can feel especially itchy or burning.
Research indicates that the disease may result from a disorder in the immune system. The immune system makes white blood cells that protect the body from infection. In psoriasis, the T cells (a type of white blood cell) abnormallytrigger inflammation in the skin. These T cells also cause skin cells to grow faster than normal and to pile up in raised patches on the outer surface of the skin.
Those with a family history of psoriasis have an increased chance of having the disease. Some people carry genes that make them more likely to develop psoriasis. When both parents have psoriasis, the child may have a 50% chance of developing psoriasis. About one third of those with psoriasis have at least one family member with the disease.
Certain factors may trigger psoriasis.
- Injury to the skin: Injury to the skin has been associated with plaque psoriasis. For example, a skin infection, skin inflammation, or even excessive scratching can trigger psoriasis.
- Sunlight: Most people generally consider sunlight to be beneficial for their psoriasis. However, a small minority find that strong sunlight aggravates their symptoms. A badsunburn may worsen psoriasis.
- Streptococcal infections: Some evidence suggests that streptococcal infections may cause a type of plaque psoriasis. Thesebacterial infections have been shown to cause guttate psoriasis, a type of psoriasis that looks like small red drops on the skin.
- HIV: Psoriasis typically worsens after an individual has been infected with HIV. However, psoriasis often becomes less active in advanced HIV infection.
- Drugs: A number of medications have been shown to aggravate psoriasis. Some examples are as follows:
- Lithium - Drug that may be used to treat depression.
- Beta-blockers - Drugs that may be used to treat high blood pressure.
- Antimalarials - Drugs used to treat malaria.
- NSAIDs - Drugs, such as ibuprofen (Motrin and Advil) or naproxen(Aleve), used to reduce inflammation.
- Emotional stress: Many people see an increase in their psoriasis when emotional stress is increased.
- Smoking: Cigarette smokers have an increased risk of chronic plaque psoriasis.
- Alcohol: Alcohol is considered a risk factor for psoriasis, particularly in young to middle-aged males.
- Hormone changes: The severity of psoriasis may fluctuate with hormonal changes. Disease frequency peaks during puberty and menopause. Apregnant woman's symptoms are more likely to improve than worsen, if any changes occur at all. In contrast, symptoms are more likely to flare in thepostpartum period, if any changes occur at all.