Alopecia areata is typically diagnosed through a visual examination of the hair loss patches, without the need for extensive testing. A dermatologist can usually identify it in a single office visit based on the shape, texture, and pattern of the bald spots, along with a few simple in-office checks. Blood tests and biopsies are reserved for cases where the diagnosis is unclear or another condition needs to be ruled out.
What the Patches Look Like
The classic sign is one or more smooth, round or oval bald patches that appear suddenly, usually on the scalp. Unlike fungal infections or scarring conditions, the skin underneath looks normal: no redness, no scaling, no scarring. The patches develop over a few weeks and can range from a coin-sized spot to much larger areas.
One of the most telling features is the presence of “exclamation mark” hairs at the edges of a patch. These are short, broken hairs that are narrower at the base and wider at the tip, giving them a tapered, exclamation-point shape. They’re considered a hallmark of alopecia areata and signal that the condition is actively progressing. You might also notice short, fine hairs regrowing within older patches, sometimes with a coiled or curly texture even if your hair is normally straight.
Alopecia areata doesn’t always follow the typical round-patch pattern. In the ophiasis pattern, hair loss wraps around the back and sides of the head in a band shape. The reverse of this, called sisaipho, affects the top and front of the scalp while sparing the back. A diffuse pattern causes rapid thinning across the entire scalp rather than distinct patches, which can make it harder to distinguish from other types of hair loss.
The Hair Pull Test
This is a quick bedside test your dermatologist will likely perform. They’ll grasp a small bundle of about 50 to 60 hairs between their fingers and apply gentle traction from the scalp outward. If more than five or six hairs come out easily, the test is positive, meaning hair loss is active. The test is repeated in different areas of the scalp to map where shedding is most severe.
For accurate results, you should avoid washing your hair for at least 24 hours before the appointment. A positive pull test doesn’t confirm alopecia areata on its own, but combined with the appearance of the patches, it helps your dermatologist gauge how active the condition is and where it’s headed.
Trichoscopy: A Closer Look at the Scalp
Trichoscopy uses a handheld magnifying device (essentially a specialized digital microscope) to examine the scalp and hair follicles up close. It’s painless and takes just a few minutes, but it reveals patterns invisible to the naked eye that can confirm the diagnosis with high confidence.
The features a dermatologist looks for include:
- Yellow dots: Round, yellowish spots at the follicle openings, caused by a buildup of oil and dead skin cells. These are the most common trichoscopic finding in alopecia areata and appear at every stage of the disease.
- Black dots: Tiny dark specks where hairs have broken off right at the scalp surface. Along with exclamation mark hairs, black dots are strong indicators that the condition is actively worsening.
- Exclamation mark hairs: The same tapered hairs visible to the naked eye, but easier to confirm under magnification.
- Short vellus hairs: Fine, light-colored hairs that signal regrowth is beginning. Sometimes these regrowing hairs curl into a pigtail shape.
Trichoscopy is also valuable for telling alopecia areata apart from conditions that can look similar. Fungal scalp infections (tinea capitis) produce comma-shaped, corkscrew, or zigzag hairs under magnification, none of which appear in alopecia areata. Trichotillomania (compulsive hair pulling) can produce black dots and a few yellow dots, but the yellow dots are far less numerous than in alopecia areata, and the broken hairs have irregular lengths rather than the characteristic tapered shape.
When a Scalp Biopsy Is Needed
Most people with alopecia areata never need a biopsy. It’s reserved for cases where the hair loss pattern is unusual, trichoscopy is inconclusive, or the dermatologist needs to rule out a scarring form of hair loss. The procedure involves removing a small plug of scalp tissue, typically a few millimeters wide, under local anesthesia.
Under a microscope, alopecia areata has a distinctive appearance: clusters of immune cells surrounding the hair bulbs deep in the skin, a pattern pathologists describe as a “swarm of bees.” The biopsy also shows a shift in the hair growth cycle, with an abnormally high proportion of follicles in their resting or shedding phases, and signs of damage to the hair-producing cells at the base of the follicle. These findings together are enough to confirm the diagnosis definitively.
Blood Tests and Autoimmune Screening
There’s no blood test that diagnoses alopecia areata directly. However, because it’s an autoimmune condition, it overlaps with other autoimmune disorders, particularly thyroid disease. Many dermatologists will order a panel that includes thyroid-stimulating hormone (TSH), a complete blood count, ferritin (to check iron stores), and vitamin D levels. These tests won’t tell you whether you have alopecia areata, but they can catch related conditions that might be contributing to hair loss or that need treatment on their own.
There are currently no evidence-based guidelines directing exactly which lab tests to order or how cost-effective broad autoimmune screening is. The decision is typically based on your symptoms, family history, and whether your dermatologist suspects a coexisting condition.
How Severity Is Measured
Once alopecia areata is confirmed, your dermatologist will assess how much hair you’ve lost using the SALT score (Severity of Alopecia Tool). The scalp is divided into four quadrants, and the percentage of hair loss in each quadrant is multiplied by that quadrant’s proportion of total scalp area. The four values are added together. A score of 0 means no hair loss, while 100 means complete scalp hair loss.
The SALT score matters because it influences treatment decisions. Mild cases (small, isolated patches) are managed differently from extensive ones, and the score gives both you and your dermatologist a consistent way to track whether hair loss is progressing, stable, or improving over time. It also serves as a baseline: if you start treatment, follow-up SALT scores show objectively whether it’s working.
Conditions That Look Similar
Several other types of hair loss can mimic alopecia areata, and part of the diagnostic process is ruling them out.
Tinea capitis, a fungal infection of the scalp, also creates patchy hair loss with black dots. But it usually comes with scaling, redness, itching, or even pus-filled bumps, none of which are typical of alopecia areata. Under trichoscopy, the comma-shaped and corkscrew hairs of tinea capitis are unmistakable. A fungal culture or scraping confirms it when there’s any doubt.
Trichotillomania produces irregular patches of broken hairs at varying lengths, often in areas easy to reach with the hands (the top and sides of the scalp, eyebrows, eyelashes). The patches tend to have more jagged borders than the smooth, round patches of alopecia areata. Trichoscopy helps here too: the abundance of yellow dots in alopecia areata far exceeds what’s seen in trichotillomania.
Diffuse alopecia areata can be mistaken for telogen effluvium, a common form of temporary shedding triggered by stress, illness, or hormonal changes. The key difference is that telogen effluvium causes widespread thinning without distinct bald patches, and trichoscopy won’t show the yellow dots or exclamation mark hairs characteristic of alopecia areata.