Your physician can usually diagnose the form based on your symptoms and a careful skin examination. But a biopsy is sometimes needed for confirmation. Most people have just one kind of psoriasis, but you can develop a new type of the skin disorder at any time. (1) Between 80 percent and 90 percent of people with psoriasis have this form, according to the American Academy of Dermatology. (2) Plaque psoriasis is characterized by raised, scaly patches of skin. On white skin, the patches, known as plaques, are often red or pink, with silvery-white scale. On skin of color plaques may appear salmon with silvery-white scale, or violet or dark brown with gray scale. Plaques can crop up on any area of the body but are commonly found on the knees, elbows, scalp, or back. The plaques can cause:

BurningPainItchinessCrackingBleeding

It affects about 10 percent of people with psoriasis, according to the National Psoriasis Foundation (NPF). (3) Guttate psoriasis, from the Latin for “raindrop shaped,” causes small, dot-like spots on the body. These lesions frequently appear on the upper arms, trunk, thighs, or scalp. Often, this form of psoriasis starts in childhood or young adulthood. Guttate psoriasis can be triggered by a strep infection, tonsillitis, stress, a skin injury, or certain medication (such as beta-blockers). Sometimes genetic factors are to blame. Guttate psoriasis may clear up on its own, but certain cases require treatment. Some patients may experience guttate psoriasis just once, while others may find it leads to plaque psoriasis. Pustular psoriasis is characterized by pus-filled bumps (called pustules) surrounded by inflamed and reddened or otherwise discolored skin. These blisters contain white blood cells and are not infectious or contagious. (4) The bumps may cause:

SorenessPain

The pustules can appear on any part of the body but most often show up on the hands or feet. When the bumps dry out, they can leave behind brown dots or scales on the skin. Some triggers may increase your risk of developing this form of psoriasis. These include:

Systemic steroid medicationSuddenly stopping the use of certain medication, including topical steroid medicinesPregnancyInfectionStressToo much sunlightCertain chemicals

Occasionally, the pustules can cover the entire body, which is known as generalized pustular psoriasis, or von Zumbusch psoriasis. This is a serious condition that requires immediate medical attention. Symptoms of generalized pustular psoriasis include:

FeverNauseaChillsBright red skinFatigueMuscle weaknessSevere itchingLoss of appetiteFast heart rate

These lesions typically appear on creased areas of the body where skin meets skin, such as the underarms, behind the knees, under the breasts, near the buttocks and genitals, or on the groin. This condition can cause sore skin, which may worsen if you sweat or rub the area. It’s sometimes triggered by a buildup of yeast. Some people who develop inverse psoriasis also suffer from another form of psoriasis. (5) This type usually occurs in people who have uncontrolled plaque psoriasis. Erythrodermic psoriasis causes extremely red or otherwise discolored skin that affects most of the body. (6) Symptoms include:

BurningPeelingSevere itchingPainFast heart rateChange in body temperature

If you have erythrodermic psoriasis, you’ll need immediate treatment, as it can be a life-threatening condition. This form of psoriasis can cause complications, such as protein and fluid loss, infection, pneumonia, severe swelling, or congestive heart failure. Erythrodermic psoriasis may be triggered by:

A severe sunburnAn allergic reaction to a medicineSuddenly stopping psoriasis treatmentAn infectionCertain drugs, such as lithium, cortisone, antimalarial medicines, or coal tar products

This type can cause symptoms such as:

Discoloration of nailsRed or white spots underneath the nailsAbnormal nail growthPitting (small pinprick holes) on nailsRidges or grooves in your nailsLifting of the nail away from the skinCrumbling of nails

Many people with plaque psoriasis also have nail psoriasis. For some, however, a single nail involvement may be the only form of psoriasis they develop. About half of people who have psoriasis have it on their scalp. At the onset, scalp psoriasis often is confused with seborrheic dermatitis (aka dandruff). Dandruff is a flaky, itchy scalp without signs of inflammation (such as discoloration or swelling). Scalp psoriasis can spread beyond the hairline and affect the forehead, back of the neck, and areas around the ears. Often psoriasis in kids is first found on the scalp. Additional reporting by George Vernadakis