Psoriasis is a skin condition that causes raised and scaly patches to appear on your skin. Psoriasis is chronic, meaning there is no cure, but there are many treatment options available to manage your symptoms. The right treatment approach depends on your psoriasis severity and type.

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

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 score system, but having a basic understanding of the score could be helpful as you pursue psoriasis treatment options. Let’s go over the basics of this widely used test.

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

Your PASI score indicates the following:

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

The PASI result 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.

  • 0: no involvement
  • 1: 1 to 9 percent of the area has psoriasis present
  • 2: 10 to 29 percent of the area has psoriasis present
  • 3: 30 to 49 percent of the area has psoriasis present
  • 4: 50 to 69 percent of the area has psoriasis present
  • 5: 70 to 89 percent of the area has psoriasis present
  • 6: 90 to 100 percent of the area has psoriasis present

For example, if 25 percent 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.

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.

Pros of PASI

  • It provides a measurement that can be used to track whether a treatment is managing symptoms effectively or not.
  • It’s easy to perform with a visual assessment in a dermatologist’s office. No fancy equipment or pricy diagnostics are necessary.

Cons of PASI

  • Some say this test is not as objective as it could be, with scores varying according to how experienced the physician scoring it is.
  • If you have psoriasis that limits your quality of life, even if it does not cover a large amount of your body area, the test has no way to account for this.
  • Scores over 40 are rare and the test in general skews low, which makes it difficult to use this test to compare psoriasis cases to each other.

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 percent 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.

Common treatments for psoriasis include:

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.

Here are some questions to ask a doctor if treatment is not improving your psoriasis.

The PASI score is one metric that dermatologists use to understand how severe your psoriasis symptoms are. It’s used as a way to decide which treatment options to try, as well as to see if the treatment is working.

If you are concerned about your psoriasis symptoms or would like to try a different treatment approach, you should speak 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 impact your quality of life in many ways, from lowering your confidence to causing uncomfortable physical symptoms. There are management and treatment options available.

The PASI score may help you better understand your psoriasis and feel empowered in managing it.