How to tell apart these distinct but related conditions
Psoriasis is a skin condition that can take many forms. Most people live with just one of the types below, although there are rare cases in which a patient may experience more than one type.
The most common type of psoriasis is plaque psoriasis. Nearly 90% of the people who live with psoriasis have this kind. Plaque psoriasis shows up as dry, red, raised lesions covered in silvery white scales that may shed. It usually appears on the elbows, knees, scalp, or lower back, although it can crop up anywhere, including the genitals and inside the mouth.
Up to 10% of people with psoriasis have guttate, the second most common type of the disease, which usually affects people under 30. In this form, the plaques are smaller and resemble water drops, and typically develop suddenly, often following a cold or upper respiratory tract infection. One of the major triggers of guttate psoriasis is strep throat. The plaques usually appear on the trunk, arms, legs, and scalp, and may be covered in a finer scale than those in plaque psoriasis.
Inverse psoriasis (also called seborrheic psoriasis)
Inverse psoriasis develops in skin folds such as the armpits, groin, under the breasts, around the genitals and buttocks, and sometimes behind the ears. It is exacerbated by friction and sweating. Most common in people who are overweight, it often starts out very red without much scale, and may appear shiny.
White blisters surrounded by red skin are the hallmarks of pustular psoriasis. The skin generally turns red first and then quickly develops noncontagious pustules filled with white blood cells. It usually covers a large swatch of skin and is sometimes accompanied by fever, chills, and severe itching. The blisters may clear quickly but reappear often.
This type of psoriasis has several triggers, including pregnancy and medications such as systemic steroids. Flares may also occur after stopping the use of certain medications, such as strong topical steroid creams.
The least common form of psoriasis results in inflammation, itching, and a painful red rash that may peel and often covers the entire body. Sometimes accompanied by chills and unregulated body temperature, it can result from severe sunburn, withdrawal from systemic treatment, or another form of psoriasis that is not well controlled. People with erythrodermic psoriasis should seek immediate medical attention because it can lead to dangerous protein and fluid loss, swelling, infection, or pneumonia, and can require hospitalization.
Up to 30% of people with psoriasis also have psoriatic arthritis, which usually develops five to 10 years after the original psoriasis diagnosis (although it can show up before a skin diagnosis). The primary symptoms are pain and stiffness in a joint or joints. Morning stiffness, which can take 45 minutes to loosen up, and tendinitis are two other signs.
If a person with psoriasis develops joint symptoms that last more than a few weeks, they should be evaluated to see if they have developed psoriatic arthritis. People with mild psoriasis might be just as likely to develop arthritis as someone with a severe form of the disease. Although psoriatic arthritis is not as debilitating as other forms of arthritis, it should be controlled to minimize pain and maximize joint function.