Psoriasis is usually classified on a scale from mild to severe. There’s no consensus on how to define psoriasis severity, though. Learn how doctors determine psoriasis severity and how psoriasis severity influences your treatment options.

Psoriasis is a chronic condition that involves the immune system and causes an atypical increase in the growth of skin cells. It may also result in systemic inflammation or affect other organ systems, such as the joints.

Psoriasis plaques are a hallmark feature of the skin condition. They’re large skin patches that are raised and may be:

  • scaly
  • itchy
  • dry
  • pink, red, purple, or dark brown, depending on your skin tone

There are many types of psoriasis, and they can range in severity. If you’re newly diagnosed, one big question you may have is: “How severe is my psoriasis?”

Psoriasis severity can vary greatly from person to person. In general, psoriasis is classified on a scale from mild to severe.

However, there’s no current consensus on how to define psoriasis severity. The condition can be challenging for a doctor to classify.

Your classification depends on many factors, including:

  • how much surface area the condition covers
  • which body part is involved or the location of psoriasis on your skin
  • your specific physical symptoms
  • how it affects your personal life

Mild psoriasis covers up to 3% of your body while moderate psoriasis covers 3% to 10%, according to the National Psoriasis Foundation.

Psoriasis may range from red scaly patches to dark red areas that have an overlay of thick silvery-gray scales.

Topical treatments, like corticosteroids and vitamin D analogues, often work well in treating mild to moderate psoriasis.

Psoriasis is generally considered severe when it affects more than 10% of your body. Psoriasis may also be considered severe if it:

  • cannot be treated with topical medications alone
  • appears on or in certain locations like the scalp, hands, feet, groin, or between the skin folds
  • has a significant impact on your quality of life

Severe psoriasis typically requires systemic as well as topical treatment.

Systemic medications treat the entire body. They include immunosuppressants and immunomodulators (such as biologics and biosimilars). Biologics are a popular treatment option for moderate to severe plaque psoriasis.

Did you know?

The surface of your hand represents about 1% of your body surface area (BSA).

You can use your hand as a quick “tool” to estimate whether your psoriasis is mild (covering up to 3% of your body), moderate (covering 3% to 10%), or severe (covering over 10%).

If you have psoriasis, your doctor will assess the severity of your condition. They’ll also ask how your psoriasis affects your physical, psychological, and social well-being.

Your doctor may assess your psoriasis severity by looking at your physical symptoms. They may check for:

  • erythema, or redness
  • scaling
  • induration, or lesion thickness

These symptoms are often used to determine psoriasis severity.

They should also:

  • ask if you’re having any joint symptoms like pain
  • look at your nails for evidence of psoriasis

These symptoms can indicate whether your psoriasis is systemic.

There are no exact ways of measuring psoriasis severity, but various tools are available to help your doctor classify your condition.

The ones described below may become an important part of your treatment plan. Newer and less cited assessments are also currently being created.

Body surface area (BSA) assessments

BSA assessments measure the total area of your body affected by psoriasis.

Doctors often rely on the naked eye when making these assessments.

However, the use of computerized images may result in even more accurate assessments, according to one study. Machine learning is another promising technique that may help doctors determine psoriasis severity with better accuracy.

Physician’s Global Assessment (PGA)

During the Physician’s Global Assessment (PGA), a doctor will evaluate your lesions for redness, scaling, and thickness. They’ll also observe how your psoriasis responds to treatment.

There are many variations on the PGA. It may use a 5-, 6-, or 7-point scale.

Your psoriasis will be classified as one of the following, depending on which scale was used:

  • clear
  • nearly clear
  • mild
  • moderate
  • severe
  • very severe

Psoriasis Area and Severity Index (PASI)

The Psoriasis Area and Severity Index (PASI) is the most widely used tool for calculating the severity of psoriasis.

It’s primarily used in clinical trials. Researchers can use the PASI to determine the efficacy of a medication.

Because it’s complex and time-consuming, the PASI is rarely used in clinical settings. In addition, the PASI is not approved for use in children and teens under 18 years old.

PASI assessment takes these factors into account:

  • how much of your BSA is affected by psoriasis
  • the extent of the raised skin patches
  • the hardness and scaliness of the raised skin patches

To complete the assessment, a doctor must take 16 measurements and perform 13 calculations.

Possible scores range from 0 to 72, with a score of 5 to 10 representing moderate disease and a score over 10 representing severe disease.

The PASI is a complex tool, and getting accurate calculations can be tricky.

In 2004, a group of researchers proposed a simplified PASI (SPASI), which would only require four measurements. The SPASI hasn’t been widely adopted.

Self-administered PASI (SAPASI)

The Self-administered PASI (SAPASI) is a PGA-like tool that helps you assess your psoriasis on your own.

One company is developing a digitized version for possible use in clinical trials. Participants would go to an online platform and indicate which parts of their body are currently covered by psoriasis. This information would then be sent to the clinical researchers.

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

These short assessments measure the impact of psoriasis on your physical, psychological, and social well-being. They consist of only 10 questions, which you’ll answer yourself. When you’re done, your doctor will assess your responses.

The Dermatology Life Quality Index (DLQI) is used for people ages 16 years and older.

The Children’s Dermatology Life Quality Index (CDLQI) is used for children and teens ages 4 to 16 years. It’s also available in a cartoon version, which may appeal to younger children. A parent or guardian may need to help some children and teens complete the questionnaire.

If psoriasis is affecting your mental well-being or causing symptoms beyond the skin (like joint pain), do not hesitate to discuss it with your doctor.

By knowing how severe your psoriasis is, your doctor can better choose a treatment that will work well for you. Certain treatments work better on mild to moderate psoriasis, while more powerful drugs are more suitable for treating moderate to severe psoriasis.

Keep in mind that, depending on your insurance plan, you may not be immediately eligible to receive more powerful (and, oftentimes, more expensive) drugs like biologics. You may first have to take less expensive (and less powerful) treatments and show that those medications failed to help you manage your symptoms.