Losing between 50 and 150 hairs a day is normal, so some hair in your shower drain or on your pillowcase isn’t cause for alarm. But if you’re suddenly finding clumps in your brush or noticing your ponytail feels thinner, something has likely pushed a larger-than-usual number of hair follicles into their resting phase at the same time. This type of increased shedding, called telogen effluvium, is the most common reason otherwise healthy people experience a noticeable jump in hair loss.
How Hair Shedding Actually Works
Your hair follicles cycle through three phases: growing, transitioning, and resting. At any given time, roughly 85 to 90 percent of your hair is in the growing phase, which lasts two to six years. The rest is in the resting phase, waiting to fall out and make room for a new strand. When something disrupts this cycle, a large batch of growing hairs gets pushed into the resting phase all at once. Two to four months later, those hairs fall out together, and you notice dramatic shedding that seems to come out of nowhere.
This delay is key. The trigger that caused your shedding likely happened months before you noticed extra hair on your brush. That time gap makes it harder to connect the dots, which is why so many people are caught off guard.
The Most Common Triggers
Telogen effluvium is a reaction to some kind of physical or emotional stress on the body. The list of documented triggers is long, but the most frequent ones fall into a few categories.
Physical illness or surgery. A high fever, severe infection, or major surgical procedure can shock enough follicles into the resting phase to cause visible shedding a few months later. COVID-19 became a well-known trigger for this reason.
Hormonal shifts. Postpartum shedding is one of the most recognized forms. During pregnancy, elevated estrogen keeps more hair in the growing phase than usual, which is why many people enjoy thicker hair while pregnant. After delivery, estrogen drops and all that “extra” hair enters the resting phase at once. Shedding typically starts around three months postpartum and resolves within 6 to 12 months. Stopping birth control pills can produce a similar, smaller-scale effect.
Crash dieting and low protein intake. Rapid weight loss or severely restricting calories signals to your body that resources are scarce. Hair growth is not essential for survival, so follicles get deprioritized. This is one of the more common and underrecognized triggers.
Emotional stress. Prolonged psychological stress can disrupt the hormonal and inflammatory signals that keep follicles in their growth phase. A divorce, job loss, grief, or sustained anxiety can all be enough.
Nutritional Deficiencies That Fuel Shedding
Low iron is one of the best-studied nutritional links to hair shedding. In one study, women with diffuse hair loss had an average ferritin level (the protein that stores iron) of about 15 ng/mL, compared to 25 ng/mL in healthy controls. Your ferritin can technically fall within the “normal” lab range and still be too low for optimal hair growth. If you menstruate heavily, eat little red meat, or donate blood regularly, iron is worth checking.
Vitamin D also plays a role, though the evidence is strongest for patchy hair loss rather than diffuse shedding. People with significant hair loss consistently show lower vitamin D levels than healthy controls in multiple studies, and lower levels correlate with more severe loss.
Zinc deficiency is a well-established cause of hair loss, and supplementing zinc restores growth when levels are genuinely low. About 10 percent of people with telogen effluvium in one study were zinc-deficient. Researchers have suggested that levels below 70 µg/dL are strongly correlated with shedding. Zinc is found in meat, shellfish, seeds, and legumes, so strict vegetarians and people with gut absorption issues are at higher risk of running low.
Excess vitamin A, interestingly, can also trigger shedding. Retinoid medications and high-dose vitamin A supplements are documented culprits.
Thyroid Problems and Hair Changes
Both an underactive and overactive thyroid can cause hair shedding, but the hair itself looks different in each case. Hypothyroidism slows down cell division in the follicle, producing hair that grows slowly, feels coarse and brittle, and looks dull. You might also notice thinning in the outer third of your eyebrows, which is a classic sign. Shedding happens because hairs get stuck in the resting phase longer and new growth is delayed.
Hyperthyroidism, on the other hand, tends to make hair fine and silky before it falls out. The overactive thyroid generates oxidative stress that damages follicles and weakens hair shafts. In both cases, the shedding is diffuse, meaning it happens all over the scalp rather than in patches. If your shedding comes with fatigue, weight changes, or temperature sensitivity, a thyroid panel is a reasonable next step.
Medications That Can Cause Shedding
A number of commonly prescribed medications list hair loss as a side effect. Blood thinners are among the most well-documented, with shedding reported anywhere from three weeks to three months after starting them. Beta-blockers (used for blood pressure and anxiety) have been linked to hair loss in case reports, though it appears to be uncommon. Mood stabilizers, certain antifungal medications, and retinoids used for acne or skin conditions are also on the list.
If your shedding started a few months after beginning a new medication, that timing is worth mentioning to your prescriber. Medication-induced telogen effluvium is typically reversible once the drug is stopped or switched, but that’s a decision to make with your doctor rather than on your own.
Scalp Inflammation Plays a Role
Chronic scalp conditions like seborrheic dermatitis (the more severe cousin of dandruff) can contribute to shedding. The mechanism is straightforward: ongoing inflammation around the follicle disrupts its normal cycle. Seborrheic dermatitis breaks down the skin barrier on the scalp, triggers a low-grade inflammatory state, and can push hairs into the resting phase prematurely. If your shedding comes with itching, flaking, or redness on the scalp, treating the inflammation often helps slow the hair loss.
How to Tell If Your Shedding Is Excessive
A simple test you can do at home: run your fingers through clean, dry hair and tug gently. If one or two hairs come out, that’s normal. If you’re pulling out noticeably more with each pass, that suggests active shedding beyond the baseline rate. In a clinical setting, a doctor grasps about 50 to 60 hairs and pulls gently. More than 5 or 6 hairs coming out indicates a positive test and active hair loss.
Pay attention to where the shedding is happening. Telogen effluvium is diffuse, thinning evenly across the scalp. If you’re losing hair in distinct patches, or if you see broken hairs rather than hairs with a small white bulb at the root, something else may be going on.
How Long the Shedding Lasts
The good news is that telogen effluvium is almost always self-limiting. The shedding phase typically lasts three to six months after it starts, and hair regrows on its own once the trigger is removed or resolved. Because the follicles themselves are undamaged, regrowth is the rule rather than the exception.
The full timeline from trigger to recovery looks something like this: the triggering event happens, then two to four months of apparent normalcy pass before shedding begins. Shedding continues for three to six months, then gradually tapers. New growth fills in over the following months. From start to finish, you’re looking at roughly 6 to 12 months before your hair feels like it’s back to normal. If shedding persists beyond six months without improvement, it may have become chronic, which warrants a closer look at ongoing triggers like nutrient deficiencies, thyroid dysfunction, or sustained stress.
What You Can Do Now
Start by thinking back three to four months. Did you have a major illness, surgery, or stressful event? Did you start a new medication, go on a restrictive diet, or give birth? Identifying the trigger is the single most useful step, because removing or resolving it is what allows the cycle to reset.
If no obvious trigger comes to mind, basic bloodwork can rule out the most common underlying causes. Iron (ferritin specifically, not just a standard iron panel), vitamin D, zinc, and thyroid function cover the major nutritional and hormonal contributors. These are straightforward tests that any primary care provider can order.
In the meantime, eating enough protein, keeping iron and zinc intake adequate, and managing stress where possible all support the hair growth cycle. Avoid crash diets, and if you’re taking a biotin supplement hoping it will help, know that biotin deficiency is actually rare and supplementing it doesn’t improve shedding unless you’re genuinely deficient. Focus on the nutrients with stronger evidence behind them: iron, zinc, vitamin D, and adequate protein.