Androgenetic Alopecia vs Telogen Effluvium: Key Differences

If your hair is thinning or shedding more than usual, there is roughly an 85% chance (Piraccini & Alessandrini, 2014, Journal of the American Academy of Dermatology) the cause is one of two conditions: androgenetic alopecia (AGA) or telogen effluvium (TE). They look different, behave differently, and require entirely different responses. AGA is a slow, progressive miniaturization of hair follicles driven by genetics and hormones. TE is a sudden, diffuse shedding episode triggered by a specific physiological stressor. Getting the distinction right early shapes every tracking, treatment, and dermatologist conversation that follows.

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Two conditions, two completely different mechanisms

Androgenetic alopecia is genetic. It is driven by dihydrotestosterone (DHT), a hormone that binds to androgen receptors in susceptible hair follicles and causes them to shrink over successive growth cycles. Each cycle produces a thinner, shorter strand until the follicle can only generate fine vellus hair or stops producing hair altogether. Sinclair et al. (2011, British Journal of Dermatology) showed that the ratio of miniaturized to terminal hairs is the most reliable diagnostic marker for AGA, often detectable years before thinning becomes visible to the naked eye.

Telogen effluvium works through an entirely different pathway. A physiological shock, such as major surgery, high fever, severe emotional stress, crash dieting, childbirth, or starting/stopping certain medications, pushes an abnormally large percentage of hair follicles from the active growth phase (anagen) into the resting phase (telogen) simultaneously. Whiting (2001, Journal of the American Academy of Dermatology) classified TE into acute (lasting under six months) and chronic forms, noting that the hallmark is diffuse shedding across the entire scalp rather than patterned loss in specific zones.

The critical difference: AGA is a permanent, progressive condition that requires ongoing management. TE is typically self-limiting and resolves once the triggering stressor is removed or resolved. Confusing the two leads to either unnecessary panic (treating TE as if it were permanent baldness) or dangerous complacency (assuming AGA will resolve on its own like TE).

Pattern of loss: localized vs. diffuse

AGA follows predictable geographic patterns on the scalp. In men, it typically starts at the temples and crown, matching the areas where follicles have the highest concentration of androgen receptors. The Norwood-Hamilton scale maps seven stages of this progression, from minor temple recession to complete vertex baldness with only a horseshoe of remaining hair. In women, AGA usually presents as widening of the central part with preservation of the frontal hairline, classified by the Ludwig scale into three grades. You can assess your own pattern using our Norwood scale self-assessment guide.

TE, by contrast, causes diffuse shedding across the entire scalp. There is no characteristic pattern. Hair comes out evenly from the front, sides, crown, and back. You might notice more hairs on your pillow, in the shower drain, or when running your fingers through your hair, but the scalp itself does not show the localized thinning zones typical of AGA. If you are losing density uniformly, TE is more likely. If you can see scalp through your crown but not through the sides, AGA is the stronger candidate.

Onset speed: gradual vs. sudden

AGA unfolds across years or even decades. Most men with AGA start noticing changes in their late 20s or early 30s, but the miniaturization process often begins in the late teens. The progression is so gradual that many people do not notice until a photograph from three years ago reveals a difference. This slow tempo is why structured monthly photo tracking catches AGA changes that daily mirror checks miss entirely.

TE has a dramatic, fast onset. The triggering event occurs, and two to four months later (the time it takes for telogen hairs to complete their resting phase and detach), shedding increases sharply. You might go from losing 50-100 hairs per day (the normal range) to 200-400. The delay between trigger and shedding is why many people struggle to connect the cause. A stressful event in January produces visible shedding in March or April. Our guide on stress and hair loss explains this timing gap in detail.

The pull test: a simple at-home check

The hair pull test is one of the simplest clinical assessments, and you can do a version of it at home. Grasp a small bundle of about 40-60 hairs between your thumb and forefinger, close to the scalp. Apply firm, steady traction as you slide your fingers to the tips. Count the hairs that come out.

In a healthy scalp, you should get zero to two hairs per pull. In active TE, the pull test is strongly positive: you will typically extract six or more hairs per pull, and those hairs will have club-shaped (rounded, white) bulbs at the root, confirming they are telogen hairs that were in the resting phase. In AGA, the pull test is usually negative or only mildly positive, because AGA does not dramatically increase the rate of shedding. Instead, it changes the quality of the hairs that grow back.

Repeat the pull test in multiple areas: temples, crown, sides, and back. If results are uniformly positive across all regions, TE is more likely. If the pull test is positive at the crown and temples but negative at the sides and back, you may be seeing AGA-related miniaturization with some concurrent shedding.

Hair caliber: the miniaturization signature

The single most important distinction between AGA and TE is what happens to hair caliber. In AGA, the hairs that grow back from affected follicles are progressively thinner, shorter, and lighter with each cycle. If you part your hair at the crown or temples and see thick terminal hairs growing next to thin, wispy hairs in the same patch, that mixed-caliber pattern is a strong signal of miniaturization.

In TE, the hairs that shed are normal-caliber terminal hairs, and the hairs that grow back are also normal-caliber. The follicle itself is not damaged or shrinking. It was simply pushed into the resting phase prematurely. Once the trigger resolves and the follicle re-enters anagen, it produces the same thick strand it always did. If your shed hairs are consistently thick and pigmented rather than thin and wispy, TE is the more likely diagnosis.

Timeline to recovery: months vs. never (without treatment)

Acute TE typically resolves within six to nine months after the triggering stressor ends. The follicles re-enter the growth phase on their own schedule, and most patients see noticeable regrowth by month four to six. Our TE recovery timeline guide breaks down what to expect at each monthly checkpoint. Chronic TE, defined as shedding persisting beyond six months, requires investigation into ongoing triggers such as thyroid dysfunction, iron deficiency, or sustained psychological stress.

AGA does not resolve on its own. Without treatment, it progresses. The rate varies between individuals, some men lose significant density within five years while others progress slowly over decades, but the direction is always toward further miniaturization and coverage loss. Treatment with finasteride, minoxidil, or both can slow progression and sometimes partially reverse it, but stopping treatment typically leads to resumed loss within 6 to 12 months.

Can you have both at the same time?

Yes, and this is more common than most people realize. A person with early-stage AGA who experiences a major stressor can develop TE on top of their existing pattern loss. The result is a sudden acceleration of visible thinning that feels far worse than either condition alone. The TE component sheds large volumes of hair quickly, while the AGA component means some of those follicles will regrow thinner hairs when they re-enter the growth phase.

This overlap is one of the strongest reasons to track both shedding volume and hair caliber as separate metrics. If shedding decreases after a few months (suggesting TE resolution) but the regrowing hairs are thinner than the originals (suggesting AGA), you are likely dealing with both conditions. That information changes treatment decisions and is exactly the kind of nuance a structured tracking log captures that memory alone cannot.

What to track for each condition

If you suspect TE, focus your tracking on shedding volume over time. Count or estimate hairs lost per wash day, log context factors (stress levels, diet changes, medications, illness), and take diffuse photos under consistent lighting to watch for density recovery. The trend you are looking for is a peak in shedding followed by a gradual decline back to baseline over three to six months. Use our telogen effluvium recovery tracker to build this timeline.

If you suspect AGA, focus on targeted zone photography. Capture the same angles (hairline, temples, crown, part line) under the same lighting monthly. Look for changes in scalp visibility, hairline position, and hair caliber variation within zones. The trend you are looking for is gradual progression or stabilization in response to treatment. Use our early signs tracker or diffuse thinning tracker depending on your presentation.

When to see a dermatologist

Self-assessment gives you a useful starting framework, but a definitive diagnosis often requires a clinical evaluation. A dermatologist can perform trichoscopy (a magnified scalp examination) to directly measure the miniaturized-to-terminal hair ratio, which Sinclair et al. (2011) identified as the gold standard for distinguishing AGA from other causes. They can also order blood work to rule out thyroid disorders, iron deficiency, and other systemic conditions that can cause or worsen TE.

You should schedule an appointment if shedding has persisted for more than six months with no identifiable trigger, if you notice patterned thinning concentrated at the hairline or crown, if you are female with a widening part line, or if self-assessment suggests both conditions might be present. Arriving with three to six months of structured tracking data, photos, shedding logs, and context notes, makes the consultation significantly more productive. See our tracking fundamentals guide for setup instructions.

Quick reference: AGA vs. TE at a glance

The bottom line

Androgenetic alopecia and telogen effluvium are the two most common causes of hair loss, and they require opposite responses. AGA demands early, sustained treatment and long-term tracking to measure stabilization. TE demands patience, trigger identification, and recovery monitoring to confirm the shedding wave is subsiding. Both benefit enormously from structured photo tracking, but the metrics you focus on, the timeline you expect, and the decisions you make based on your data are fundamentally different.

Start by identifying your pattern (localized vs. diffuse), assessing your onset speed (gradual vs. sudden), checking hair caliber (mixed vs. uniform), and noting any recent stressors. That initial assessment points you toward the right tracking framework and gives your dermatologist a head start if you need professional evaluation. Start by identifying your pattern with the early signs tracking page.