Why Is My Hair Falling Out?

Three patterns cover most adult hair loss, and you can tell them apart by what you see in the mirror and what happened a few months back. Androgenetic alopecia is gradual, patterned thinning. Telogen effluvium is a diffuse shed that follows a trigger. Alopecia areata is patchy loss from an autoimmune attack. None of these is diagnosed by a supplement bottle. So before you reach for zinc or blame your shampoo, look at where the hair is thinning and what changed in the months before it started.

Gradual thinning that follows a pattern

Androgenetic alopecia is the most common form of hair loss worldwide. Among people of European descent, some reviews estimate it affects up to about 80% of men and roughly half of women by age 70; it's lower in Asian populations. Follicles that are genetically sensitive to androgens like dihydrotestosterone gradually shrink, so each cycle produces a thinner, shorter hair until the follicle makes almost nothing. In men that's receding temples and a thinning crown. In women it's usually a widening part and diffuse thinning on top, with the front hairline spared.

Pattern loss is slow and progressive, and diet usually doesn't explain it by itself unless a separate deficiency or medical problem is present. So the first useful question is whether you want to slow it, not which supplement to try. It's also not caused by the things people fear. A 12-week randomized trial of resistance-trained young men found no DHT or hair-growth signal from creatine, addressing a worry raised by an earlier small study that had reported a short-term rise in DHT. Shampooing makes shedding more visible, but it doesn't cause inherited pattern loss. Harsh styling and chemical treatments are a separate problem: they break hair and can injure the scalp.

Shedding that shows up months after the trigger

Telogen effluvium is why hair loss so often feels mysterious. A physical or emotional shock pushes a big batch of follicles into their resting phase at once, but they don't release the old hairs until 2 to 3 months later. By the time you're shedding handfuls in the shower, the event that caused it has faded from your mind. The classic triggers: a high fever, childbirth, surgery, severe dieting or rapid weight loss, thyroid disease, iron deficiency, and some medications. COVID-19 too, usually with the same delayed pattern.

This is also the right frame for hair loss on the newer weight-loss drugs. The Wegovy and Zepbound labels list hair loss in weight-reduction trials: 3.3% to 5.8% in Wegovy groups and 4% to 5% across Zepbound doses, versus about 1% on placebo. The labels also say the reactions were associated with weight reduction and reported more often in women than men. That doesn't prove a direct follicle effect; it is more consistent with reactive shedding after rapid weight loss. And acute telogen effluvium is self-limiting. Once the trigger passes, most follicles restart, and shedding usually settles within about six months without treatment.

Patches, and an autoimmune signal

Alopecia areata is different in kind. The immune system attacks the follicles, producing round, smooth bald patches that can appear quickly. Roughly 1% to 2% of people develop it at some point. The follicle isn't destroyed, so regrowth is possible, but this one needs an in-person exam, and it often travels with other autoimmune conditions. Hashimoto's thyroiditis, vitiligo, and atopic disease all show up more often alongside it, and thyroid autoimmunity has been linked with more severe or longer-lasting disease in retrospective cohorts. Don't wait for a supplement to work while an autoimmune pattern is spreading.

Where testing and supplements actually help

Testing earns its place when the pattern and history point to a treatable medical cause, which mostly means diffuse shedding rather than slow patterned thinning. If you're shedding diffusely, check your thyroid function, iron studies including ferritin, and vitamin D, especially with fatigue, weight change, heavy periods, a restricted diet, recent rapid weight loss, or no obvious trigger. Iron is usually treated when ferritin is clearly low, with many dermatologists using a threshold around 40 ng/mL, rather than topping up a normal level. There's no single agreed cutoff, and that figure rests on expert practice, not trial data.

The supplement aisle is where a pattern-first approach saves you money and, sometimes, a misdiagnosis. For adults without a confirmed deficiency, single-nutrient supplements like biotin, zinc, iron, vitamin D, and collagen haven't been shown to reliably reverse hair loss. Zinc is a good example of why small supplement studies are not the same as a reason to self-treat: alopecia areata studies point in different directions, with both negative and positive reports, and the evidence still doesn't support routine zinc without a documented deficiency. Biotin has no good trial support outside true deficiency, and it distorts thyroid and cardiac lab tests, which matters precisely when you're trying to find the cause. Overdoing vitamin A, vitamin E, or selenium can even worsen shedding. A supplement fixes a deficiency you've documented. It doesn't substitute for figuring out what's happening.

Hair loss can cause distress out of proportion to the physical problem, and that's a legitimate reason to act. Acting well means starting from the pattern: where the hair is thinning, what changed a few months ago, and whether there's a treatable trigger or medical cause when the clues fit. What would change this advice is straightforward. Large trials showing that correcting borderline nutrient levels, changing sleep or metabolic risk, or stopping a specific drug reliably reverses a defined hair-loss pattern. Until then, the pattern and timeline are where you start.