Psoriasis Area and Severity Index (PASI) Score

The right treatment approach for psoriasis depends on your severity and type. The Psoriasis Area and Severity Index (PASI) score is a tool dermatologists use to classify psoriasis and help determine treatment.

Classifying psoriasis can be difficult and subjective. However, dermatologists use several tools to categorize it according to agreed-upon standards. One of these tools is the Psoriasis Area and Severity Index (PASI) score.

The PASI score aims to objectively measure the severity of your psoriasis. It’s often used in clinical trials to determine if a new psoriasis treatment is working well or not.

Your PASI score is based on how much of your body is affected by psoriasis, how your scales appear, and other factors.

You don’t need to learn the math formula behind the PASI scoring system, but having a basic understanding of the score is useful as you pursue psoriasis treatment options. This article reviews the basics of this widely used metric.

A PASI score can range from 0 to 72. However, while 72 is technically the highest option, scores over 40 are considered rare.

• 0 to 5: none to mild psoriasis
• 6 to 10: moderate psoriasis
• 11 or above: severe psoriasis

A PASI score is calculated via a complicated math formula. It uses information your dermatologist acquires through a physical examination of your psoriasis. Your doctor will do the calculations for you, likely with the help of a computer.

Area calculation

Your doctor will assess your entire body for visible psoriasis symptoms to get what’s called an “area calculation” of your symptoms. Four different regions of your body will be scored individually.

These regions are:

• head
• upper extremities (arms and hands)
• trunk (torso)
• lower extremities (legs and feet)

Your doctor will look for psoriasis scales on each of these areas and give each area a score on a scale of 0 to 6.

For example, if 25% of your arms and hands are covered in psoriasis scales, your doctor would mark your condition down as a “2” in the upper extremities region. If you did not have any psoriasis present on your legs or feet, your condition would be scored a “0” in the lower extremities region.

The table below provides more detail on what determines your area calculation score.

Intensity calculation

In addition to how much of your body area has psoriasis involvement, your symptom severity is also ranked with a number from 0 to 4. The symptom severity score of each area is based on:

• redness
• swelling
• thickness of your psoriasis scales

While the PASI score seeks to be as objective as possible, there are still parts of the score that are subjective. This means they are still centered on your doctor’s opinion and evaluation of your psoriasis.

It’s important you get evaluated by an expert, usually a dermatologist. Skin experts will know exactly what to look for and will have context for the range of psoriasis severity.

Yes, a PASI score can change over time. Successful treatments can bring down your score.

If you reach a milestone called “PASI 75,” it means that your psoriasis has improved by 75% compared to how severe it was before treatment. PASI 75 is not a specific score scale but a benchmark for treatment success.

The Physician’s Global Assessment (PGA) is another scoring method for psoriasis. This score is obtained by grading each area of psoriasis on your body for scaling, swelling or redness, and hardness.

The numbers are then averaged together and divided by 3. The result will be a number between 0 and 4, with 4 being the most severe.

The PGA provides a simple (although not comprehensive) picture of how severe your psoriasis symptoms are at a given point in time. Some dermatologists feel that the PGA is more subjective than the PASI, but both tools can be useful.

Your first-line treatment for psoriasis will be based in part on your PASI score.

For mild to moderate psoriasis, a doctor will often prescribe topical treatments and lifestyle changes first. For people with severe psoriasis or psoriasis that does not respond to conservative treatment approaches, doctors may recommend oral and injectable medications and light therapies.

Even though the PASI score can help identify what treatment might be the best first option for you, it’s important to remember everyone’s body is different. No one responds the exact same way to different medications or therapies. It may take some exploring to find what works best for you.

Always communicate with your doctor about any changes in symptoms or side effects you are experiencing during treatment for psoriasis.

The PASI score is one metric dermatologists use to understand how severe your psoriasis symptoms are. It’s used to decide which treatment options to try and to determine whether the treatment is working.

If you are concerned about your psoriasis symptoms or would like to try a different treatment approach, you should talk with a doctor. This is also true if you do not have a psoriasis diagnosis but are experiencing any troubling skin changes, including redness, scaling, or itching.

Skin conditions like psoriasis can affect your quality of life in many ways, from lowering your confidence to causing uncomfortable physical symptoms. Management and treatment options are available.

The PASI score may help you better understand your psoriasis and feel empowered to manage it.