PASI Score for Psoriasis

PASI scores are a way to rate the severity of your psoriasis

Dermatologist working at a spa
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psoriasis area and severity index (PASI) score is a value used by clinicians to determine how severe your psoriasis is. Psoriasis is a common skin condition that changes the life cycle of skin cells. Psoriasis causes cells to build up rapidly on the surface of the skin. The extra skin cells form thick, silvery scales and itchy, dry, red patches that are sometimes painful.

PASI scores are typically used during clinical trials and less so by practicing physicians.

To determine your PASI score, your doctor will rate how severe your psoriasis by evaluating three features of a psoriatic plaque. Your doctor will look at the plaque's redness, scaling, and thickness, assigning each feature a number from 0 to 4 with 4 being worst. Then the extent of involvement of each region of the body is scored from 0 to 6. Once these numbers have been tallied, your doctor will add up all of the scores for a final value, which will range from 0 to 72.


Psoriasis is a persistent, long-lasting chronic disease. There may be times when your psoriasis symptoms get better alternating with times your psoriasis worsens. Psoriasis signs and symptoms can vary from person to person but may include one or more of the following:

  • Red patches of skin covered with silvery scales
  • Small scaling spots (commonly seen in children)
  • Dry, cracked skin that may bleed
  • Itching, burning, or soreness

Psoriasis patches can range from a few spots of dandruff-like scaling to major eruptions that cover large areas. Most types of psoriasis go through cycles, flaring for a few weeks or months, then subsiding for a time or even going into complete remission.

Risk Factors

Anyone can develop psoriasis, but these factors can increase your risk of developing the disease:

  • Family history. Having one parent with psoriasis increases your risk of getting the disease, and having two parents with psoriasis increases your risk even more.
  • Viral and bacterial infections. Having HIV makes you more likely to develop psoriasis. Children and young adults with recurring infections, particularly strep throat, also have an increased risk.
  • Stress. Because stress can impact your immune system, high-stress levels may increase your risk of psoriasis.
  • Obesity. Excess weight increases the risk of psoriasis. 
  • Smoking. Smoking tobacco not only increases your risk of psoriasis but also may increase the severity of the disease. Smoking may also play a role in the initial development of the disease.

Improving Your PASI Score

Typically in studies, when there is an improvement in a person's PASI score it's because of a drug's effectiveness. For example, researchers may note that a certain proportion of patients experienced a 75 percent reduction in their PASI scores over a 12-week treatment period.

PASI scores are seldom used in clinical practice, although more fastidious doctors or those working at university-based clinics or specialized psoriasis treatment centers may routinely use this tool to follow their patients' progress.


Mayo Clinic. Psoriasis. 2016.