Psoriasis is an autoimmune condition that causes the skin to produce cells at an accelerated rate, leading to thick, raised patches known as plaques. These plaques can be itchy, painful, and affect various parts of the body. Over 7.5 million adults in the United States are estimated to have psoriasis, though the actual number may be higher due to underdiagnosis.

This condition can resemble other skin issues like eczema, making diagnosis more challenging—especially in people with darker skin tones, where symptoms may look different. If you suspect you may have psoriasis, it’s important to consult a healthcare provider. A dermatologist will typically conduct a physical exam, review your medical history, and may recommend a skin biopsy to confirm the diagnosis.

Medical history

Your healthcare provider will begin by asking questions about your overall health, family history, and any recent changes in your life. This step helps them understand your background and assess potential triggers.

Common questions include:

  • Do you have a family history of psoriasis?

  • Have you experienced any major life stressors recently?

  • When did your symptoms begin, and how have they progressed?

You may also be asked about joint-related symptoms such as swelling, stiffness, or pain. These can indicate psoriatic arthritis, a condition that co-occurs with psoriasis in many individuals.

Physical exam

A dermatologist will visually inspect your skin, scalp, and nails to check for plaques, scaling, or rashes. Many cases of psoriasis can be diagnosed just by looking at the skin.

Skin appearance can vary depending on skin tone. In lighter skin, plaques may appear pink or red with silvery-white scales. In darker skin, plaques may look purple, brown, or gray, often with thicker or rougher texture.

Dermatologists may use a dermatoscope—a handheld device with a magnifying lens and light—to closely examine suspicious areas.

Since psoriasis is sometimes underdiagnosed in people with darker skin, many healthcare providers now rely on additional tools and resources, such as the Skin of Color Resource Center, to support accurate diagnosis across all skin tones.

Skin biopsy

Because psoriasis can resemble conditions like eczema or contact dermatitis, your provider may perform a skin biopsy to confirm the diagnosis. This involves removing a small section of affected skin to be analyzed under a microscope.

Types of biopsy include:

Punch biopsy
A circular blade is used to take a deeper sample of skin, especially useful for thicker plaques.

Shave biopsy
A razor-like instrument removes a sample from the surface layers. This method is typically used for superficial plaques.

Before the procedure, the skin is cleaned and numbed with local anesthesia. Most people experience only mild discomfort, and side effects such as soreness or minor bruising usually subside within a few days.

Screening for related conditions

In addition to diagnosing psoriasis, your provider may assess for related health issues, such as allergies or psoriatic arthritis.

Patch testing
While not needed to confirm psoriasis, patch testing may help identify coexisting skin conditions. During the test, small amounts of potential allergens are applied to your skin, typically on the back, and covered with patches.

These patches stay in place for 48 to 72 hours. Your provider will later examine the area to see if there are any reactions, which could indicate allergies, eczema, or other conditions.

Imaging tests
Tests such as X-rays or MRIs are not used to diagnose psoriasis itself but may be helpful in detecting psoriatic arthritis. Around one-third of people with psoriasis also develop this joint condition.

Imaging is often done to examine areas like the hands, knees, or feet—particularly the smaller joints in early PsA. If damage or inflammation is detected, your provider may refer you to a rheumatologist and coordinate care with a dermatologist.

A quick review

Psoriasis is a chronic skin disease characterized by raised, thick plaques. Diagnosis is based on a combination of methods, including medical history, physical examination, and sometimes skin biopsy. Additional tests like patch testing or imaging may help identify related conditions.

If you notice symptoms like red, scaly patches or experience joint pain, consulting a healthcare provider early can make a big difference. A timely diagnosis not only helps relieve discomfort but also prevents complications and improves quality of life.