Psoriasis is a common skin disease that affects the life cycle of skin cells. Psoriasis causes cells to build up rapidly on the surface of the skin, forming thick silvery scales and itchy, dry, red patches that are sometimes painful. Psoriasis is a persistent, long-lasting (chronic) disease. You may have periods when your psoriasis symptoms improve or go into remission alternating with times your psoriasis worsens. For some people, psoriasis is just a nuisance. For others, it's disabling, especially when associated with arthritis. There's no cure, but psoriasis treatments may offer significant relief. Lifestyle measures, such as using a nonprescription cortisone cream and exposing your skin to small amounts of natural sunlight, can improve your psoriasis symptoms. The cause of psoriasis isn’t fully known, but it's thought to be related to the immune system and its interaction with the environment in people who have the genetic susceptibility. More specifically, one key cell is a type of white blood cell called a T lymphocyte or T cell. Normally, T cells travel throughout the body to detect and fight off foreign substances, such as viruses or bacteria. If you have psoriasis, however, the T cells attack healthy skin cells by mistake, as if to heal a wound or to fight an infection.
Overactive T cells trigger other immune responses. The effects include dilation of blood vessels in the skin around the plaques and an increase in other white blood cells that can enter the outer layer of skin. These changes result in an increased production of both healthy skin cells and more T cells and other white blood cells. This causes an ongoing cycle in which new skin cells move to the outermost layer of skin too quickly — in days rather than weeks. Dead skin and white blood cells can't slough off quickly enough and build up in thick, scaly patches on the skin's surface. This usually doesn't stop unless treatment interrupts the cycle. Just what causes T cells to malfunction in people with psoriasis isn't entirely clear, although researchers think genetic and environmental factors both play a role. Psoriasis typically starts or worsens because of a trigger that you may be able to identify and avoid. Factors that may trigger psoriasis include: infections, such as strep throat or thrush, injury to the skin, such as a cut or scrape, bug bite, or a severe sunburn, stress, cold weather, smoking, heavy alcohol consumption, certain medications — including lithium, which is prescribed for bipolar disorder; high blood pressure medications such as beta blockers; antimalarial drugs; and iodides. Psoriasis signs and symptoms can vary from person to person but may include one or more of the following: red patches of skin covered with silvery scales, small scaling spots (commonly seen in children), dry, cracked skin that may bleed, itching, burning or soreness, thickened, pitted or ridged nails, swollen and stiff joints. Psoriasis patches can range from a few spots of dandruff-like scaling to major eruptions that cover large areas. Mild cases of psoriasis may be a nuisance; more-severe cases can be painful, disfiguring and disabling. Most types of psoriasis go through cycles, flaring for a few weeks or months, then subsiding for a time or even going into complete remission. In most cases, however, the disease eventually returns. Several types of psoriasis exist. These include: Plaque psoriasis. The most common form, plaque psoriasis causes dry, raised, red skin lesions (plaques) covered with silvery scales. The plaques itch or may be painful and can occur anywhere on your body, including your genitals and the soft tissue inside your mouth. You may have just a few plaques or many, and in severe cases, the skin around your joints may crack and bleed. Nail psoriasis. Psoriasis can affect fingernails and toenails, causing pitting, abnormal nail growth and discoloration. Psoriatic nails may become loose and separate from the nail bed (onycholysis). Severe cases may cause the nail to crumble. Scalp psoriasis. Psoriasis on the scalp appears as red, itchy areas with silvery-white scales. You may notice flakes of dead skin in your hair or on your shoulders, especially after scratching your scalp. Guttate psoriasis. This primarily affects people younger than 30 and is usually triggered by a bacterial infection such as strep throat. It's marked by small, water-drop-shaped sores on your trunk, arms, legs and scalp. The sores are covered by a fine scale and aren't as thick as typical plaques are. You may have a single outbreak that goes away on its own, or you may have repeated episodes, especially if you have ongoing respiratory infections. Inverse psoriasis. Mainly affecting the skin in the armpits, in the groin, under the breasts and around the genitals, inverse psoriasis causes smooth patches of red, inflamed skin. It's more common in overweight people and is worsened by friction and sweating. Pustular psoriasis. This uncommon form of psoriasis can occur in widespread patches (generalized pustular psoriasis) or in smaller areas on your hands, feet or fingertips. It generally develops quickly, with pus-filled blisters appearing just hours after your skin becomes red and tender. The blisters dry within a day or two, but may reappear every few days or weeks. Generalized pustular psoriasis can also cause fever, chills, severe itching and fatigue. Erythrodermic psoriasis. The least common type of psoriasis, erythrodermic psoriasis can cover your entire body with a red, peeling rash that can itch or burn intensely. It may be triggered by severe sunburn, by corticosteroids and other medications, or by another type of psoriasis that's poorly controlled. Psoriatic arthritis. In addition to inflamed, scaly skin, psoriatic arthritis causes pitted, discolored nails and the swollen, painful joints that are typical of arthritis. It can also lead to inflammatory eye conditions, such as conjunctivitis. Symptoms range from mild to severe, and psoriatic arthritis can affect any joint. Although the disease usually isn't as crippling as other forms of arthritis, it can cause stiffness and progressive joint damage that in the most serious cases may lead to permanent deformity. In most cases, diagnosis of psoriasis is fairly straightforward. Physical exam and medical history. Your doctor usually can diagnose psoriasis by taking your medical history and examining your skin, scalp and nails. Skin biopsy. Rarely, your doctor may take a small sample of skin (biopsy) that's examined under a microscope to determine the exact type of psoriasis and to rule out other disorders. A skin biopsy is usually done in a doctor's office using a local anesthetic. Psoriasis treatments can be divided into three main types: topical treatments, light therapy and systemic medications. Topical treatments can be used alone, creams and ointments that you apply to your skin can effectively treat mild to moderate psoriasis. When the disease is more severe, creams are likely to be combined with oral medications or light therapy. Light therapy uses natural or artificial ultraviolet light. The simplest and easiest form of phototherapy involves exposing your skin to controlled amounts of natural sunlight. Other forms of light therapy include the use of artificial ultraviolet A (UVA) or ultraviolet B (UVB) light either alone or in combination with medications. Systematic medications may be prescribed oral or injected drugs. Because of severe side effects, some of these medications are used for only brief periods and may be alternated with other forms of treatment.