Psoriasis signs and symptoms are different for everyone. Common signs and symptoms include:

• Red patches of skin covered with thick, 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.

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.

There are several types of psoriasis. These include:

• Plaque psoriasis. The most common form, plaque psoriasis causes dry, raised, red skin lesions (plaques) covered with silvery scales. The plaques might be itchy or painful and there may be few or many. They can occur anywhere on your body, including your genitals and the soft tissue inside your mouth.
• Nail psoriasis. Psoriasis can affect fingernails and toenails, causing pitting, abnormal nail growth and discoloration. Psoriatic nails might loosen and separate from the nail bed (onycholysis). Severe cases may cause the nail to crumble.
• Guttate psoriasis. This type primarily affects young adults and children. It's usually triggered by a bacterial infection such as strep throat. It's marked by small, water-drop-shaped, scaling lesions on your trunk, arms, legs and scalp.

The lesions 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.

• Inverse psoriasis. This mainly affects the skin in the armpits, in the groin, under the breasts and around the genitals. Inverse psoriasis causes smooth patches of red, inflamed skin that worsen with friction and sweating. Fungal infections may trigger this type of psoriasis.
• 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 may come and go frequently. Generalized pustular psoriasis can also cause fever, chills, severe itching and diarrhea.

• 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.
• Psoriatic arthritis. In addition to inflamed, scaly skin, psoriatic arthritis causes swollen, painful joints that are typical of arthritis. Sometimes the joint symptoms are the first or only manifestation of psoriasis or at times only nail changes are seen. 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.

The cause of psoriasis isn't fully understood, but it's thought to be related to an immune system problem with T cells and other white blood cells, called neutrophils, in your body.

T cells normally travel through the body to defend against foreign substances, such as viruses or bacteria.

But if you have psoriasis, the T cells attack healthy skin cells by mistake, as if to heal a wound or to fight an infection.

Overactive T cells also trigger increased production of healthy skin cells, more T cells and other white blood cells, especially neutrophils. These travel into the skin causing redness and sometimes pus in pustular lesions. Dilated blood vessels in psoriasis-affected areas create warmth and redness in the skin lesions.

The process becomes an ongoing cycle in which new skin cells move to the outermost layer of skin too quickly — in days rather than weeks. Skin cells build up in thick, scaly patches on the skin's surface, continuing until treatment stops the cycle.

Just what causes T cells to malfunction in people with psoriasis isn't entirely clear. Researchers believe both genetics and environmental factors play a role.

Psoriasis triggers

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 skin infections
• Injury to the skin, such as a cut or scrape, a bug bite, or a severe sunburn
• Stress
• Smoking
• Heavy alcohol consumption
• Vitamin D deficiency
• Certain medications — including lithium, which is prescribed for bipolar disorder, high blood pressure medications such as beta blockers, antimalarial drugs, and iodides

Anyone can develop psoriasis, but these factors can increase your risk of developing the disease:

• Family history. This is one of the most significant risk factors. Having one parent with psoriasis increases your risk of getting the disease, and having two parents with psoriasis increases your risk even more.
• Viral and bacterial infections. 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, also may be at increased risk.
• Stress. Because stress can impact your immune system, high stress levels may increase your risk of psoriasis.
• Obesity. Excess weight increases the risk of psoriasis. Lesions (plaques) associated with all types of psoriasis often develop in skin creases and folds.
• Smoking. Smoking tobacco not only increases your risk of psoriasis but also may increase the severity of the disease. Smoking may also play a role in the initial development of the disease.

If you have psoriasis, you're at greater risk of developing certain diseases. These include:

• Psoriatic arthritis. This complication of psoriasis can cause joint damage and a loss of function in some joints, which can be debilitating.
• Eye conditions. Certain eye disorders — such as conjunctivitis, blepharitis and uveitis — are more common in people with psoriasis.
• Obesity. People with psoriasis, especially those with more severe disease, are more likely to be obese. It's not clear how these diseases are linked, however. The inflammation linked to obesity may play a role in the development of psoriasis. Or it may be that people with psoriasis are more likely to gain weight, possibly because they're less active because of their psoriasis.
• Type 2 diabetes. The risk of type 2 diabetes rises in people with psoriasis. The more severe the psoriasis, the greater the likelihood of type 2 diabetes.
• High blood pressure. The odds of having high blood pressure are higher for people with psoriasis.
• Cardiovascular disease. For people with psoriasis, the risk of cardiovascular disease is twice as high as it is for those without the disease. Psoriasis and some treatments also increase the risk of irregular heartbeat, stroke, high cholesterol and atherosclerosis.
• Metabolic syndrome. This cluster of conditions — including high blood pressure, elevated insulin levels and abnormal cholesterol levels — increases your risk of heart disease.
• Other autoimmune diseases. Celiac disease, sclerosis and the inflammatory bowel disease called Crohn's disease are more likely to strike people with psoriasis.
• Parkinson's disease. This chronic neurological condition is more likely to occur in people with psoriasis.
• Kidney disease. Moderate to severe psoriasis has been linked to a higher risk of kidney disease.
• Emotional problems. Psoriasis can also affect your quality of life. Psoriasis is associated with low self-esteem and depression. You may also withdraw socially.