How Psoriasis is Diagnosed

Because psoriasis causes such distinctive changes in the appearance of the skin, hair, or nails, it usually is obvious when a person develops the condition. This means that in the majority of cases, a doctor can diagnose psoriasis by taking a medical history and doing a physical exam. Only rarely will a biopsy be necessary to pin down a psoriasis diagnosis.

Self-Checks/At-Home Testing

If you develop a rash or changes on your scalp or nails, it can be helpful to have an idea of what the different types of psoriasis look like—especially if you aren't familiar with the varieties that don't cause the scaly plaques that most people associate with psoriasis.

For example, about half of people who have psoriasis on other parts of their body also will have scalp patches. But it's possible to develop psoriasis on the scalp only, in which case it can be confused with other conditions, such as seborrheic dermatitis. Seborrhea on the scalp usually appears less thick and crusty than scalp psoriasis. The flakes of seborrhea usually are yellow or white, whereas those of psoriasis are a silvery-gray.

Nail psoriasis sometimes is mistaken for a nail fungus. In fact, according to the National Psoriasis Foundation (NSF), about a third of people with nail psoriasis also have a fungal infection.

And although people with skin psoriasis often develop nail psoriasis, it's possible to have psoriasis of the nails only, so it's important not to discount that possibility if you have symptoms such as pitting (dents), thickening, changes in shape, discoloration, or separation of the nail from the nail bed.

A rash that consists of pale pink, teardrop-shaped spots could be guttate psoriasis. This type of psoriasis, which usually follows a bacterial or viral infection such as strep throat, is most common in children and people under 30.

A type of psoriasis called pustule psoriasis looks much like it sounds: Areas of reddened skin covered in pus-filled blisters that often are confined to the soles of the feet or palms of the hands. If you develop this type of rash all over your body along with symptoms such as fever, chills, and dehydration, get medical help immediately. You may have a form of pustular psoriasis called von Zumbusch psoriasis that can require hospitalization.

In general, any rash, especially one that's persistent or seems to come out of nowhere, should be evaluated by a doctor. These are just some of the examples of how differently psoriasis can look depending on the type. 

View Article Sources
  • Mayo Clinic. Psoriasis: Diagnosis. Mar 6, 2018. https://www.mayoclinic.org/diseases-conditions/psoriasis/diagnosis-treatment/drc-20355845 .
  • National Psoriasis Foundation. Hands, Feet, and Nails. www.psoriasis.org/about-psoriasis/specific-locations/hands-feet-nails.