What is a PASI Score?

PASI score: Psoriasis Area and Severity Index

Dermatologist. Joe Raedle / Staff / Getty Images

What is a PASI Score?

The PASI score stands for Psoriasis Area and Severity Index.

What is Psoriasis?

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.

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 Symptoms

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
  • Thickened, pitted or ridged nails
  • Swollen and stiff joints

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 For Psoriasis

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. People with HIV are more likely to develop psoriasis than people with healthy immune systems are. Children and young adults with recurring infections, particularly strep throat, also may be at 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.

How PASI Score Works

This tool allows researchers to put an objective number on what would otherwise be a very subjective idea: how bad is a person's psoriasis. To make up the score, the three features of a psoriatic plaque (redness) scaling and thickness are each assigned 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. Adding up the scores give a range of 0 to 72.

Improving PASI Score

Many studies quote the improvement seen in the PASI score over time as a measure of a drug's effectiveness. For example, they may note that a certain proportion of patients experienced a 75 percent reduction in their PASI scores over a 12-week treatment period and report this as a percentage of people achieving "PASI 75."

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. http://www.mayoclinic.org/diseases-conditions/psoriasis/basics/definition/con-20030838

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