Diagnosing alopecia starts with a dermatologist examining your scalp, asking detailed questions about your health history, and often performing simple in-office tests that take just minutes. Because “alopecia” is an umbrella term covering dozens of hair loss conditions, the real diagnostic challenge isn’t confirming that you’re losing hair. It’s figuring out which type you have, whether it’s reversible, and what’s driving it.
What Your Doctor Learns From Your History
Before touching your scalp, a dermatologist will spend time asking questions that narrow down the type of hair loss. The timing of when your shedding started is one of the most important clues. Telogen effluvium, the most common cause of sudden diffuse shedding, typically shows up about three months after a triggering event. Your doctor will ask about high fevers, childbirth, major surgery, severe infections, psychological stress, crash diets low in protein, and recent medication changes. Certain drug classes are known triggers, including blood pressure medications, antidepressants, retinoids, and even stopping birth control pills.
Family history matters too, especially for androgenetic alopecia (pattern hair loss), which has a strong genetic component. Your doctor will also ask about autoimmune conditions, thyroid problems, and any recent changes to your hair care routine. Traction alopecia, for example, results from hairstyles that pull on the hair over time, and that’s something only a conversation can uncover.
The Pull Test and Tug Test
Two quick hands-on tests give your dermatologist immediate information about what’s happening with your hair.
In a pull test, the doctor grasps about 60 strands of hair between their thumb and index finger and gently pulls upward. Traditionally, losing more than 10% of the grasped hairs (roughly six or more) counts as a positive result, meaning active hair loss. In practice, though, most healthy people lose zero to two hairs during this test, so even a few hairs coming out can signal a problem. Your dermatologist will repeat this in several spots across your scalp, because where the shedding is happening helps identify the type.
The tug test is different. Here, the doctor holds a section of hair with both hands, one near the root and one near the tip, and tugs to see if strands snap in the middle. This checks for brittleness and fragility rather than shedding, pointing toward conditions that damage the hair shaft itself rather than the follicle.
Trichoscopy: A Closer Look at the Scalp
Trichoscopy uses a handheld magnifying device (essentially a specialized dermoscope) to examine your scalp and hair follicles at high magnification. It’s now considered an essential part of any hair loss consultation because it reveals structures invisible to the naked eye, including changes to hair shaft thickness, skin surface abnormalities around follicles, and signs of inflammation or scarring.
Each type of alopecia has its own signature under the scope. In androgenetic alopecia, the hallmark finding is hair shaft diameter diversity: a mix of thick, healthy strands alongside numerous thin, miniaturized ones, often with about 50% variation in diameter across a given area. In alopecia areata, dermatologists look for “exclamation-mark hairs” (short broken hairs that taper to a narrow base), black dots where hairs have broken off at the surface, and yellow dots, which are empty follicles filled with oil. Yellow dots in a regular, evenly spaced pattern across a bald patch strongly suggest alopecia areata. Short regrowing hairs with thin tips that thicken toward the base can also indicate that recovery is already underway.
Scarring alopecias look entirely different. Folliculitis decalvans, for instance, shows large tufts of five or more hairs emerging from a single opening, along with pustules and redness. These findings help a dermatologist decide whether a biopsy is needed and exactly where to take it.
Scarring vs. Non-Scarring Alopecia
One of the most critical distinctions your dermatologist makes early on is whether your hair loss is scarring (cicatricial) or non-scarring. In non-scarring types like androgenetic alopecia, alopecia areata, and telogen effluvium, the hair follicles are still intact beneath the surface. The follicles may be miniaturized, dormant, or shedding prematurely, but they retain the potential to produce hair again.
In scarring alopecia, inflammation destroys the follicle and replaces it with scar tissue. Once that happens, hair cannot regrow in that spot. The scalp in affected areas often looks smooth and shiny, with no visible follicle openings. This is why early diagnosis of scarring types is so urgent: treatment can stop further destruction but can’t reverse what’s already scarred. Trichoscopy and biopsy are both especially important for catching scarring alopecia before it progresses.
Blood Tests and Lab Work
Blood tests don’t diagnose alopecia directly, but they identify underlying conditions that cause or worsen hair loss. A standard workup for someone with unexplained shedding typically includes thyroid function tests, since both an overactive and underactive thyroid can trigger significant hair loss. Iron levels (specifically ferritin, the stored form of iron) are checked because low iron is a well-known contributor to thinning, especially in women. A complete blood count can reveal anemia or nutritional deficiencies.
For women showing signs of pattern hair loss along with acne, irregular periods, or excess body hair, hormone panels measuring testosterone and related androgens help screen for conditions like polycystic ovary syndrome. Inflammatory markers or autoimmune antibody tests may be ordered if a scarring alopecia or systemic autoimmune condition is suspected. Not everyone with hair loss needs extensive lab work, but these tests are standard when the cause isn’t immediately clear from examination alone.
When a Scalp Biopsy Is Needed
A biopsy is performed whenever the diagnosis remains uncertain after examination, trichoscopy, and lab tests. It’s particularly common when a dermatologist suspects scarring alopecia or needs to distinguish between two conditions that look similar on the surface.
The procedure itself is straightforward. A small circular punch, typically 4 millimeters in diameter, removes a tiny core of scalp tissue. It’s done under local anesthesia in the office and usually requires one or two stitches. Where the sample is taken depends on the suspected diagnosis. For non-scarring types, the biopsy is taken from the area where hair is thinnest. For scarring types, the best spot is at the edge of an active lesion, where the dermatologist can capture both scar tissue and actively inflamed follicles in the same sample. Trichoscopy often guides exactly where to place the punch.
Under the microscope, a pathologist can see whether follicles are miniaturized, in the wrong phase of the growth cycle, surrounded by inflammatory cells, or replaced by scar tissue. The tissue is sliced horizontally at multiple levels to give a cross-sectional view of as many follicles as possible, which provides more diagnostic information than a vertical cut.
Advanced Hair Counting With Phototrichograms
For tracking hair loss over time or measuring treatment response, some clinics use phototrichograms. A small area of the scalp (usually one square centimeter) is clipped short, then photographed at high magnification. The images are analyzed by software that counts the total number of hairs, measures density per square centimeter, and calculates the ratio of actively growing hairs to resting hairs. A healthy scalp has roughly 80% to 90% of hairs in the growth phase at any given time, so a shift toward more resting hairs confirms excessive shedding even before it’s visible to you.
This technique is especially useful for androgenetic alopecia, where changes happen gradually and can be hard to see month to month. Comparing phototrichograms over six to twelve months gives an objective measure of whether a treatment is working, rather than relying on subjective impressions of “more” or “less” shedding.
Putting It All Together
Most alopecia diagnoses come from combining multiple pieces of evidence rather than a single definitive test. A dermatologist might recognize classic androgenetic alopecia from the pattern and trichoscopy findings alone, without needing blood work or a biopsy. Alopecia areata with its characteristic round patches and exclamation-mark hairs is often diagnosed on sight. Telogen effluvium may be confirmed through a positive pull test combined with a clear triggering event three months earlier.
More complex cases, especially suspected scarring alopecias or overlapping conditions, require layering the clinical exam with trichoscopy, blood work, and a biopsy to reach a clear answer. The process can feel slow when you’re watching your hair thin, but accurate diagnosis is what separates effective, targeted treatment from guesswork.