Psoriasis is a common chronic autoimmune disease. It causes fast growth of skin cells. It’s marked by raised, scaly, itchy, dry, and red skin patches. These patches are called psoriasis plaques.

Psoriasis is a very complex disease. There are many types of psoriasis, and they can range in severity. One big question you may have is, “How severe is my psoriasis?”

The severity of plaque psoriasis differs greatly from person to person. Certain treatments work better on mild to moderate psoriasis, while more powerful drugs help moderate to severe psoriasis. To treat your psoriasis, your doctor has to know how severe your psoriasis is.

However, it can be challenging for a doctor to classify how severe someone’s psoriasis is. There’s currently no consensus on how to define it. In general, psoriasis is classified on a scale from mild to severe. Your classification depends on many factors. These include how much surface area the condition affects and your specific physical symptoms. Keep reading for more on how psoriasis is classified.

Mild to moderate psoriasis is when plaques cover less than of your body surface area. Psoriatic plaques look like raised surfaces with a silvery cover of dead skin cells. These are called scales.

Mild to moderate psoriasis does not occur in sensitive regions on your body. These include your genitals, face, hands, and feet. Topical treatments, like corticosteroids and vitamin D analogues, often work well to treat this type of psoriasis.

When psoriasis affects more than of your body, it’s considered moderate to severe. It may affect your genitals, face, hands, and feet. Biologic drugs are a popular treatment option for this type of psoriasis. Biologics may be used alone or with other treatments to ease your psoriasis.

Learn more: Biologics for psoriasis »

If you have psoriasis, your doctor will assess how severe your condition is. They will also ask how your psoriasis affects your physical, psychological, and social well-being.

Your doctor may assess the severity by looking at your physical symptoms of psoriasis. They may look for erythema (redness), scaling, and induration (lesion thickness). These three signs are often used to classify the severity of psoriasis.

There are no exact ways to measure psoriasis severity. However, there are tools available that can help your doctor classify your condition. Other tests to measure severity include:

Body surface area (BSA)

assessments measure the total area of your body affected by psoriasis. Psoriasis that occurs on less than 5 percent of your BSA is considered mild to moderate psoriasis. If psoriasis affects more than 5 percent of your BSA, you have moderate to severe psoriasis.

Psoriasis Area and Severity Index (PASI)

is the most widely used tool for calculating the severity of psoriasis. It measures how much of your BSA is affected by psoriasis, the extent of raised red patches, and the hardness and scaling of plaques. It’s a complex tool to use, though. Getting accurate calculations can be tricky. PASI is not approved for use in children and young people.

Physician’s Global Assessment (PGA)

The is a 5-, 6-, or 7-point scale that classifies psoriasis. It classifies it as clear, nearly clear, mild, moderate, severe, or very severe.

Self-administered PASI (SAPASI)

is a PGA-like assessment. It helps people assess their psoriasis on their own.

Dermatology Life Quality Index (DLQI) and Children's Dermatology Life Quality Index (CDLQI)

These assessments check the impact of psoriasis on a person’s physical, psychological, and social well-being. is used in adults. is used in children.

Your doctor may also use some other, less-common ways to assess your psoriasis. These may include the (PASS) or the (SPASI). Newer and less-cited assessments are currently being made as well.

Your doctor will use tools to learn how severe your psoriasis is. These measurements are an important part of your treatment plan. By knowing how severe your psoriasis is, your doctor can better choose a treatment that will work for you.