RELATED STORIES • Scalp psoriasis vs. seborrheic dermatitis: How are they different? WOMEN'S HEALTH Hair/Nails/Skin • Corns and calluses • Diaper rash • Nail fungus • Shingles • Ingrown toenails • Moles • Acne • Psoriasis • Hair loss • Sweating and body odor • Rosacea • Hives and angioedema • Athlete's foot • Dermatitis/Eczema • Cold sore • Common warts • Cellulitis • Anal itching • Dandruff • Impetigo • Boils and carbuncles • Ringworm of the body • Jock itch • Plantar warts • Folliculitis • Dry skin • Actinic keratosis • Bedsores (Pressure sores) • Vitiligo • Lipoma • Tinea versicolor • Acanthosis nigricans • Molluscum contagiosum • Neurodermatitis (lichen simplex chronicus) • Morphea • Pityriasis rosea • Lichen nitidus • Bullous pemphigoid • Pyoderma gangrenosum • Lichen sclerosus • Ichthyosis vulgaris • Pilonidal cyst • Pemphigus • Sweet's syndrome • Sacral dimple • Dermatographia • Keratosis pilaris • Poison ivy rash • Lichen planus • Granuloma annulare • Dyshidrosis • Hidradenitis suppurativa • Henoch-Schonlein purpura • Hemangioma

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Psoriasis is marked by patches of thick, red skin covered with silvery scales that occur primarily on your elbows, knees, legs, lower back and scalp. Although not life-threatening, psoriasis can be painful, affect your ability to function, and cause psychological and emotional distress.

Psoriasis develops when the ordinary life cycle of skin cells accelerates. Skin cells regularly die and flake off in scales — but in people with psoriasis this process happens within days rather than weeks.

The disease is chronic, but you may have periods when psoriasis becomes worse alternating with times when it improves or goes into remission. And although no cure exists, psoriasis treatments may offer significant relief.

The majority of affected people have relatively mild psoriasis symptoms. Still, psoriasis at its worst can be painful, disfiguring and disabling.

Several types of psoriasis exist, but the most common form, plaque psoriasis, causes dry, red skin lesions (plaques) covered with silvery scales. These usually itch or feel sore and may occur anywhere on your body, including your genitals, the soft tissue inside your mouth, and your fingernails and toenails. But plaques are most common on your knees, elbows, trunk, palms, soles and scalp. You may have just a few plaques or many, and in severe cases, the skin around your joints may crack and bleed.

Other types of psoriasis have different psoriasis symptoms. They include:

• 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, waterdrop-shaped sores on your trunk, arms, legs and scalp. The sores are covered by a fine scale and aren't as thick as plaque sores 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.
• Pustular psoriasis. This rare 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, weight loss and fatigue.
• Inverse psoriasis. Mainly affecting the skin in the armpits, 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 exacerbated by friction and sweating.
• Erythrodermic psoriasis. The least common type of psoriasis, this can cover your entire body with a red, peeling rash that may itch or burn intensely. Eythrodermic psoriasis 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. 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. Adults in their 30s, 40s and 50s are most often affected, but children also can develop a form of the disease.

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, although in most cases, the disease eventually returns.

No thicker than a sheet of paper, the outermost layer of your skin — the epidermis — serves as a strong barrier between you and the environment. In addition to offering protection from trauma, harmful substances and infection, this thin layer of flesh is also an endlessly renewable resource.

Basal cells at the base of the epidermis divide to form squamous cells, which produce keratin, a hard, protective protein. As the basal cells divide, they push new squamous cells toward the surface of your skin, where they eventually shrink, flatten and die. These dead cells make up the stratum corneum, the outermost portion of the epidermis. Stratum corneum cells flake off every day and are continuously replaced by more cells.

It normally takes about a month for new cells to make their way to the stratum corneum. But for people with psoriasis, cells reach the surface in a matter of days rather than weeks. And because the old cells can't slough off quickly enough, they build up in thick red patches.

Psoriasis and T cells
Over the years, researchers have developed various theories to explain what causes psoriasis. Current thinking is that accelerated cell turnover occurs when the immune system begins focusing on healthy skin cells instead of on invading microorganisms. Ordinarily, T cells, white blood cells that circulate throughout your body, spring into defensive action when they detect foreign substances (antigens) such as viruses and bacteria attempting to enter your skin. In psoriasis, the T cells respond to your own skin cells as if they were antigens.

This initiates an immune response that includes the release of cytokines — proteins that tell skin cells to reproduce at a quickened rate. Cytokines also stimulate the activation of more T cells, recruit those cells into the skin and then cause the skin cells to release more cytokines. Blood vessels close to the skin dilate as other white cells are recruited into the skin. What results is an ongoing cycle in which new skin cells move to the stratum corneum too quickly and dead skin and white blood cells pile up on the skin's surface.

Why T cells misbehave
Just what causes T cells to misfire in people with psoriasis isn't entirely clear, although researchers think genetic and environmental factors both play a role. In people with a hereditary predisposition to the disease, certain factors can trigger the condition or make an existing problem worse. These factors include:

• Systemic infections such as strep throat
• An injury to your skin
• Certain medications, including lithium, which is prescribed for bipolar disorder, high blood pressure medications such as beta blockers, antimalarial drugs and iodides
• Stress
• Alcohol — the poor nutrition that often accompanies heavy drinking can make psoriasis worse
• Excessive sun exposure or prolonged contact with chemicals such as disinfectants and paint thinners

Perhaps the most significant risk factor for psoriasis is having a family history of the disease. About one in three people with psoriasis have a close relative who also has the condition. On the other hand, roughly the same proportion of people carries genes that have been linked to psoriasis yet never develop skin problems, indicating just how complex and perplexing psoriasis is.

Other risk factors include:

• Medications. Taking certain drugs — especially beta blockers, antimalarial medications and lithium — makes you more prone to psoriasis.
• Other medical conditions. People with HIV are more likely to develop psoriasis than people with healthy immune systems are. Children and young adults with recurring infections, particularly strep throat, may also be at increased risk.
• Stress. Because stress can have a strong impact on your immune system, high stress levels may increase your risk of psoriasis.
• Exposure to sun and toxins. Although moderate amounts of sunlight can actually help psoriasis, excessive exposure, and sunburn in particular, can trigger the disease. So can prolonged exposure to toxic chemicals.

For most people, psoriasis is a mild nuisance, but for others it can be disabling. If your skin condition is painful or makes performing routine tasks difficult, or if you're concerned about the appearance of your skin, talk to your doctor or dermatologist. Most often, psoriasis can be diagnosed with a visual exam. Sometimes, however, your doctor may take a small sample of skin (biopsy) that's then examined under a microscope to determine the exact type of psoriasis and to rule out other, similar disorders.

Psoriasis treatment can be challenging in spite of a wide range of therapeutic options. The disease is unpredictable, going through cycles of improvement and exacerbation seemingly at whim. And psoriasis treatments can be unpredictable; what works well for one person might be ineffective for someone else. Your skin can also become resistant to various therapies over time and the most potent treatments can have serious side effects.

Although doctors choose psoriasis treatments based on the type and severity of psoriasis and the areas of skin affected, the traditional approach is to start with the mildest treatments — topical creams and light therapy (phototherapy) — and then progress to stronger ones if necessary. The goal is to find the most effective way to slow cell turnover with the fewest possible side effects.

Topical treatments
Used alone, creams and ointments can effectively treat mild to moderate psoriasis. When skin disease is more severe, creams are likely to be combined with systemic drugs or phototherapy. Topical psoriasis treatments include:

• Topical corticosteroids. These powerful anti-inflammatory drugs help slow cell turnover by suppressing the immune system. Low-potency corticosteroid ointments are usually recommended for sensitive areas such as your face and for treating widespread patches of damaged skin. Your doctor may prescribe a high-potency corticosteroid ointment for small areas of your skin, for recalcitrant plaques on your hands or feet, or when other treatments fail. Although topical corticosteroids can relieve signs and symptoms of psoriasis in the short run, resistance to treatment can develop fairly quickly and withdrawal of the medication can sometimes cause the disease to flare. Long-term or excessive use can lead to thinning skin and easy bruising as well as to more serious internal side effects.
• Vitamin D analogues. These synthetic forms of vitamin D reduce skin inflammation and help prevent skin cells from proliferating. Calcipotriene (Dovonex) is a prescription cream or solution containing a vitamin D analogue that may be used alone to treat mild to moderate psoriasis or in combination with other topical medications or phototherapy.
• Anthralin. This substance is believed to normalize DNA activity in skin cells and to reduce inflammation. Originally derived from the dried stems and branches of a Brazilian tree, anthralin (Drithocreme) is now synthesized in laboratories. Its primary drawback is that it can irritate healthy skin as well as stain virtually anything it touches, including skin, clothing and bedding. For that reason doctors often recommend short-contact treatment — allowing the cream to stay on your skin for a brief time before washing it off. Anthralin is sometimes used in combination with ultaviolet (UV) light.
• Coal tar. A thick, black byproduct of the manufacture of gas and coke, coal tar is probably the oldest treatment for psoriasis. It's effective for all forms of the disease except the severe generalized pustular types. Exactly how it works isn't known. Coal tar is available with or without a prescription and has few known side effects. It's often used in combination with light therapy (Goeckerman treatment).
• Topical retinoids. These are commonly used to treat acne and sun-damaged skin, but tazarotene (Tazorac) was developed specifically for the treatment of psoriasis. Like other vitamin A derivatives, it normalizes DNA activity in skin cells. The most common side effect is skin irritation. Although the risk of birth defects is far lower for topical retinoids than for oral retinoids, your doctor needs to know if you're pregnant or intend to become pregnant while using tazarotene.
• Clobetasol propionate. This is a potent corticosteroid foam that can be used on your skin or scalp. It penetrates easily and isn't as messy as some other topical products.
• Moisturizers. By themselves, moisturizing creams won't heal psoriasis, but they can reduce itching and scaling and can help combat the dryness that results from other therapies. Moisturizers that are heavy and oily are usually more effective than lighter lotions.

Light therapy (phototherapy)
As the name suggests, this psoriasis treatment uses natural or artificial light. The simplest and easiest form of phototherapy involves exposing your skin to moderate amounts of natural sunlight. Other traditional forms of therapy include the use of broadband ultraviolet B (UVB) light either alone or in combination with coal tar.

Other types of phototherapy include:

• Psoralen UVA (PUVA) therapy. A more aggressive treatment, psoralen UVA (PUVA) therapy involves taking a light-sensitizing medication (psoralen) before exposure to ultraviolet A (UVA) light. You usually have two or three treatments a week for a prescribed number of weeks. PUVA is effective in suppressing the growth of skin cells in severe psoriasis, but long-term treatment may increase your risk of skin cancer, including melanoma, the most serious form of skin cancer. The risk of skin cancer depends on a number of factors, among them skin pigmentation, family history, total dosage of UVA over time, the concurrent use of therapies that suppress the immune system, and the amount of protection given to your face and genital areas while undergoing PUVA therapy. There may be a delay of up to 15 years after the first treatment before any cancer is detected.
• Narrow-band UVB (NBUVB) therapy. This form of phototherapy doesn't require oral medications before each treatment and so may be less likely to cause cancer. Yet much about NBUVB remains unknown because it has been in widespread use for only a few years. It's usually administered two or three times a week. Many people who would have been treated with PUVA are now being treated with NBUVB. Sometimes your doctor may also use phototherapy and oral medications such as retinoids, methotrexate or the newer immune-modulating drugs in rotation to minimize the side effects of both.
• Combination light therapy. Combining ultraviolet light with other treatments such as retinoids improves phototherapy's effectiveness. Some doctors give UVB treatment in conjunction with coal tar, an approach called the Goeckerman treatment. The two therapies together are more effective than either alone because coal tar makes skin more receptive to UVB light. Another method, the Ingram regimen, combines UVB therapy with a coal tar bath and an anthralin-salicylic acid paste that's left on your skin for several hours or overnight.

Oral medications
If you have severe psoriasis or disease that's resistant to other forms of treatment, your doctor may prescribe oral or injected drugs. Many of these have serious side effects and are generally used for brief periods of time.

• Retinoids. Related to vitamin A, this group of drugs may reduce the proliferation of skin cells in people with severe psoriasis who don't respond to other therapies. Signs and symptoms usually return once therapy is discontinued, however. And because retinoids such as acitretin (Soriatane) can cause severe birth defects, women must protect themselves from pregnancy for at least three years after taking the medication.
• Methotrexate. Taken orally or given by injection, this drug can slow the progression of arthritis in some people with psoriatic arthritis. Taken orally, it also helps symptoms of psoriasis by decreasing the production of skin cells, suppressing inflammation and inhibiting the release of histamine — a substance involved in allergic reactions. Methotrexate is generally well tolerated in low doses, but when used for long periods it can cause a number of serious side effects, including severe liver damage and decreased production of red and white blood cells and platelets. Taking 1 milligram daily of the B vitamin folic acid can reduce the risk of methotrexate-induced mouth sores or enlarged red blood cells (macrocytosis), but folic acid won't help other potential side effects such as nausea, dizziness, diarrhea and fatigue.
  
• Azathioprine. A potent anti-inflammatory drug used to prevent organ rejection after transplants, azathioprine also may be used to treat severe psoriatic arthritis. Taken long-term, azathioprine increases the risk of developing cancerous or noncancerous growths (neoplasias) and certain blood disorders. Other potential side effects include nausea and vomiting, bruising more easily than normal, and fatigue.
• Cyclosporine. Used primarily to prevent rejection of transplanted organs, cyclosporine can improve joint and skin inflammation in people with psoriatic arthritis. It works by suppressing the immune system, but the improvement stops once treatment is discontinued. Like other immunosuppressant drugs, cyclosporine increases your risk of infection and other health problems, including cancer. Cyclosporine also makes you more susceptible to kidney problems and high blood pressure — the risk increases with higher dosages and long-term therapy.
• Hydroxyurea. This medication isn't as effective as cyclosporine or methotrexate, but unlike the stronger drugs it can be used with phototherapy treatments. Possible side effects include anemia and a decrease in white blood cells and platelets. It should not be taken by women who are pregnant or planning to become pregnant.
• Immune-modulating drugs (biologics). The Food and Drug Administration has approved several immune-modulating drugs for the treatment of moderate to severe cases of psoriasis. They include alefacept (Amevive), efalizumab (Raptiva) and etanercept (Enbrel). These drugs are given by intravenous infusion or intramuscular injection, and are usually used for people who have failed to respond to traditional therapy or for people with associated arthritis. Biologics work by blocking interactions between certain immune system cells. Although they're derived from natural sources rather than chemical ones, they have strong effects on the immune system and pose the same risks as other immunosuppressant drugs. These include an increased risk of cancer and serious, even fatal, infections. Etanercept has also been linked to tuberculosis and leukocytoclastic vasculitis, an inflammatory blood vessel disorder.

Although self-help measures won't cure psoriasis, they may help improve the appearance and feel of damaged skin. These measures may benefit you:

• Follow a nutritious diet. Although researchers haven't found a clear link between diet and psoriasis, certain foods may trigger flares in some people. If you think a particular food or food group affects your skin, try eliminating it for a time. Other than that, the best dietary approach is the same one that's recommended for most people: well-balanced meals that emphasize fresh fruits and vegetables, whole grains and lean meats. Especially helpful are the right kinds of lipids, especially omega-3 fatty acids, which are essential for healthy skin. Your body doesn't produce omega-3s — instead you obtain them from food or supplements. The best dietary sources are fatty fish or fish oil capsules — particularly salmon and salmon oil — flaxseeds and flaxseed oil, walnuts, and soybean and canola oils. Some dark green leafy vegetables such as spinach, kale and broccoli contain modest amounts of omega-3s. Incorporating these foods into your diet can help dry skin, but it does even more for your overall health. Omega-3s lower triglyceride levels and reduce your risk of heart attack and stroke. They also lower blood pressure and may reduce the pain and inflammation of rheumatoid arthritis.
• Maintain a healthy weight. Being overweight increases your risk of inverse psoriasis. In addition, plaques associated with all types of psoriasis often develop in skin creases and folds.
• Take daily baths. Bathing daily can help remove scales and calm inflamed skin. Avoid hot water and harsh soaps, which can make your symptoms worse. Instead, use lukewarm water and mild, superfatted soaps that have added oils and fats. Better still, try a soap substitute. These products vary, but may include a mild synthetic detergent or an oil mixed with a wetting agent (surfactant). They typically come in a bar, gel or liquid form, and are less drying than are deodorant and antibacterial detergents. Even more important, add bath oil, oilated oatmeal, apple cider vinegar, Epsom salts or Dead Sea salts to the water and soak for at least 15 minutes.
• Use moisturizer. Blot your skin after bathing, then immediately apply a heavy, water-in-oil moisturizing cream while your skin is still moist. For very dry skin, oils may be preferable — they have more staying power than creams do and are more effective at preventing water from evaporating from your skin. Shampoos and ointments containing coal tar or salicylic acid may offer added relief but aren't as cosmetically elegant as nonmedicinal creams are.
• Avoid sun exposure. For people with psoriasis, UV rays are a blessing and a curse. A moderate amount of sunlight can significantly improve lesions but too much sun can trigger or exacerbate outbreaks and increase the risk of skin cancer. If you sunbathe, it's best to try short sessions three or more times a week. Keep a record of when and how long you're in the sun to help avoid overexposure. And be sure to protect healthy skin with a sunscreen of at least 15 SPF, paying careful attention to your ears, hands and face. Before beginning any sunbathing program, it's best to ask your doctor about the best way to use natural sunlight to treat your skin.
• Apply cortisone. Apply an over-the-counter cortisone cream 0.5 percent or 1 percent, for a few weeks when your symptoms are especially bad.