Diagnosing psoriasis

About Psoriasis

Though it may seem easy to spot a skin condition like psoriasis, it can be hard for the untrained eye to tell the difference between psoriasis and other skin disorders, such as a common rash. The only way to know for sure is to show your doctor.

How will my doctor know for sure?

In most cases, a dermatologist can diagnose psoriasis simply by looking at it. Rarely your doctor may need to remove and examine a small sample of skin tissue (biopsy) to determine the exact type and to rule out other disorders.

What about eczema? Could it be that?

Eczema is another common skin condition, that’s often confused with psoriasis. Both conditions can cause itchy, inflamed skin, but two things can help you and your doctor tell them apart:


  • Eczema most often appears in the folds of the skin, like the inside surfaces of elbows and knees. Psoriasis usually occurs on the outside surfaces of elbows and knees, as well as other areas like the scalp, palms, soles, nails, back, torso, and face.


  • The plaques of psoriasis (the raised patches) usually have well-defined edges​, which is not the case with the flatter patches of eczema​. In contrast to eczema, psoriasis skin tissue will have more depth and it will look more inflamed when biopsied.

How can I tell if my psoriasis is mild, moderate, or severe?

Only your doctor will be able to tell for sure if your psoriasis is mild, moderate or severe; however, you can get a rough sense of severity by assessing how much of your skin is affected by your psoriasis:

Mild psoriasis is when less than 3% of the skin’s surface is affected.

Moderate psoriasis is when 3% to 10% of the skin’s surface is affected.

Severe psoriasis is when more than 10% of the skin’s surface is affected.

Psoriasis may also be considered severe if it makes daily activities difficult or unmanageable. For example, small areas—like the soles of the feet—can be very problematic from day-to-day when affected.

A dermatologist can diagnose psoriasis simply by looking at it.

Tip: Your palm represents about 1% of your total body’s skin surface