Losing between 50 and 150 hairs a day is normal. If you’re pulling clumps from your brush, finding hair all over your pillow, or noticing your ponytail getting thinner, something has likely shifted your hair growth cycle. The most common reason is a type of temporary shedding called telogen effluvium, where a stressor pushes a large batch of hair follicles into their resting phase all at once. But nutritional gaps, hormonal changes, thyroid problems, and certain medications can also be behind it.
Stress-Related Shedding Is the Most Common Cause
Your body responds to major physical or emotional stress by pausing nonessential functions, and hair growth is one of the first things to go. When this happens, a large percentage of your hair follicles shift into their resting phase simultaneously. Two to three months later, those resting hairs fall out. This delay is why the shedding often feels random: by the time your hair starts falling out, you may have already recovered from whatever triggered it.
Common triggers include high fever, severe infections (including COVID), major surgery, significant psychological stress, crash diets, and childbirth. The shedding itself typically lasts three to six months, and once the underlying cause is addressed, most people see full regrowth within six to eight months without any treatment. New hairs start growing in as the old ones fall out, so you may notice short, wispy regrowth around your hairline and part while you’re still shedding.
Postpartum Hair Loss Has Its Own Timeline
During pregnancy, elevated hormones keep more of your hair in its growing phase than usual. Your hair looks thicker and fuller because fewer strands are falling out on their normal schedule. After delivery, those hormone levels drop sharply, and all the hair that was “held back” enters the resting phase together.
In a large survey-based study, postpartum shedding started around three months after delivery, peaked at about five months, and tapered off by eight months. Most people see their hair return to its pre-pregnancy thickness within the first year. The volume of hair falling out can be alarming, but it’s the body catching up on months of delayed shedding rather than a sign of permanent loss.
Low Iron and Vitamin D Are Overlooked Culprits
Your hair follicles need a steady supply of certain nutrients to keep cycling through their growth phases. Iron is one of the most well-studied. In one case-control study, women with diffuse hair shedding had average ferritin levels (the protein that stores iron in your blood) of about 15 ng/mL, compared to roughly 60 ng/mL in women without hair loss. That’s a fourfold difference. You don’t have to be clinically anemic to lose hair from low iron; your ferritin can drop enough to affect your follicles well before your red blood cell counts look abnormal on a standard blood test.
Vitamin D plays a role in creating the cells that form hair follicles. Women with nonscarring hair loss in the same research had significantly lower vitamin D levels than controls. If you eat a restricted diet, live in a northern climate, or rarely spend time outdoors, a simple blood test can reveal whether a deficiency is contributing to your shedding. Correcting it through diet or supplementation often helps, though regrowth takes several months because hair grows slowly, about half an inch per month.
The evidence on zinc is less clear-cut. Some studies show a link between low zinc and hair loss, while others don’t. It’s worth checking if you have other signs of zinc deficiency, like slow wound healing or frequent infections, but zinc supplements aren’t a reliable fix on their own.
Your Thyroid Could Be Involved
Both an overactive thyroid and an underactive thyroid can disrupt hair growth. Thyroid hormones regulate your metabolism at the cellular level, and when production swings too high or too low, hair follicles can stop growing or enter their resting phase prematurely. The result is diffuse thinning across the entire scalp rather than bald patches in one spot.
A few signs point toward a thyroid issue specifically. You might notice thinning in your eyebrows (especially the outer third), eyelashes, or body hair in addition to your scalp. Your hair texture may change, becoming dry, coarse, and brittle. And the shedding tends to be accompanied by other symptoms: fatigue, weight changes, feeling unusually cold or hot, or mood shifts. A thyroid panel blood test can confirm or rule this out quickly, and once thyroid levels are brought back to normal with medication, hair typically regrows.
Medications That Trigger Shedding
Several common drug classes can cause hair to fall out as a side effect. Retinoids (used for acne and skin conditions), blood thinners, blood pressure medications, mood stabilizers, and certain antifungal drugs are among the most frequently reported. The shedding follows the same pattern as stress-related hair loss: it starts weeks to months after beginning the medication and looks like diffuse thinning rather than patchy bald spots.
Among blood thinners specifically, one large analysis found over 1,300 reports of hair loss linked to newer oral anticoagulants, with one particular drug accounting for nearly 59% of those cases. Beta-blockers, often prescribed for heart conditions and high blood pressure, have also been linked to shedding in case reports, though the overall incidence is low. If your hair loss started within a few months of beginning a new medication, that timing is worth mentioning to your prescriber. Stopping or switching the drug usually reverses the shedding, but never discontinue a medication on your own.
Patchy Loss Points to Something Different
If your hair is falling out in distinct, round patches rather than thinning evenly, the cause is likely alopecia areata, an autoimmune condition where your immune system attacks individual hair follicles. The patches are typically small, roughly the size of a quarter, though they can merge into larger areas. Two hallmark signs help distinguish it: “exclamation point” hairs (short broken strands that are wider at the top and taper toward the scalp) and tiny black dots where hair shafts have broken off at the surface.
Alopecia areata is unpredictable. Some people lose a single patch that regrows on its own within months. Others experience recurring episodes or more extensive loss. Treatment options exist and can speed regrowth, but the course varies widely from person to person.
Warning Signs That Need Prompt Attention
Most hair shedding is temporary and reversible, but certain patterns signal something more serious. Scaling patches on your scalp, especially with redness, swelling, or oozing, can indicate a fungal infection like ringworm that needs treatment to prevent permanent damage. Pain, burning, or itching on the scalp before hair falls out may point to an inflammatory condition. And if the skin where hair has fallen out looks smooth and shiny, scarring may have occurred, which can make the loss permanent if not treated early.
A receding hairline in women, particularly along the front of the scalp, can be a condition called frontal fibrosing alopecia. Early treatment matters here because the scarring it causes is irreversible. Sudden, rapid hair loss (over days to weeks rather than months) also warrants a prompt medical evaluation, as it can signal an underlying condition that needs its own treatment beyond the hair loss itself.
What a Doctor Will Check
When you go in for hair loss, the evaluation is usually straightforward. A doctor will often start with a gentle hair pull test: grasping a small section of hair and tugging firmly. Normally, zero to two resting-phase hairs come out. If significantly more pull free, it confirms active shedding. The roots of those hairs are examined under magnification. Rounded bulbs at the base mean resting-phase hair, which points to telogen effluvium. Tapered or irregular roots suggest the hair was pulled out of its growing phase, which is abnormal and suggests a different process.
Blood work typically includes a complete blood count, ferritin, vitamin D, and thyroid function. These tests can identify or rule out the most common reversible causes in a single round of labs. If the pattern is patchy or the scalp skin looks abnormal, a small skin biopsy may be recommended to check for autoimmune or scarring conditions.