Losing between 50 and 100 hairs a day is normal. If you’re pulling clumps from your brush, clogging your shower drain, or noticing hair on your pillow every morning, you’re likely shedding well beyond that baseline. The most common reason is a condition called telogen effluvium, where a physical or emotional stressor pushes a large number of hair follicles into their resting phase at the same time, causing them to fall out weeks or months later. But several other triggers, from hormonal shifts to nutritional gaps, can do the same thing.
How Normal Shedding Differs From a Problem
Your hair follicles cycle through growth, rest, and shedding phases independently of each other. At any given time, about 85 to 90 percent of your hair is actively growing while a small percentage is resting and preparing to shed. That’s why losing up to 100 strands a day doesn’t leave a visible difference.
When something disrupts this cycle, a much larger percentage of follicles shift into the resting phase simultaneously. Two to three months later, all of those hairs fall out at once. This is telogen effluvium. You’ll notice it as diffuse thinning across your entire scalp rather than bald patches or a widening part. The shedding can feel alarming, but telogen effluvium almost never causes obvious baldness, and it’s usually reversible once the underlying trigger is addressed.
Stress and the Cortisol Connection
Emotional or physical stress is the single most common trigger. Research from Harvard’s Stem Cell Institute clarified the mechanism: your body’s primary stress hormone, cortisol, doesn’t act on hair follicle stem cells directly. Instead, it targets a cluster of cells at the base of the follicle called the dermal papilla. Under chronic stress, elevated cortisol prevents these cells from releasing a signaling molecule that normally activates hair follicle stem cells. Without that signal, the stem cells stay dormant in their resting phase far longer than usual, and hair growth stalls.
This means the problem isn’t just a one-time stressful event. Ongoing stress keeps cortisol elevated and continuously suppresses that growth signal, creating a cycle where follicles struggle to re-enter active growth. Job loss, divorce, financial strain, caregiving, sleep deprivation, and chronic illness can all keep this axis activated for months.
Postpartum Hair Loss
If you recently had a baby, the timing explains everything. During pregnancy, elevated estrogen extends the growth phase of your hair, which is why many women notice thicker, fuller hair in the second and third trimesters. After delivery, estrogen drops back to pre-pregnancy levels, and all the hair that had been held in the growth phase enters the shedding phase at once.
Postpartum shedding typically starts around three months after giving birth and resolves on its own within 6 to 12 months. It can feel dramatic, especially around the temples and hairline, but it’s a temporary hormonal reset, not permanent loss.
Iron and Ferritin Levels
Iron deficiency is one of the most overlooked causes of hair shedding in women, partly because standard blood tests can miss it. Your hemoglobin and red blood cell counts can come back completely normal while your iron stores are still too low to support healthy hair growth. The key marker is ferritin, a protein that reflects how much iron your body has in reserve.
Many labs flag ferritin as “normal” at levels as low as 12 to 20 ng/mL, but research suggests hair follicles need significantly more than that. Studies have shown that ferritin levels below 70 ng/mL are associated with disrupted hair cycling, even in women who aren’t technically anemic. Some researchers refer to this as “nonanemic iron deficiency,” a state where your body has enough iron to make red blood cells but not enough to keep hair follicles fully nourished. Women with heavy periods, plant-based diets, or recent pregnancies are especially prone to this.
Thyroid Problems and Hormonal Imbalances
Both an underactive and overactive thyroid can cause diffuse hair shedding. Thyroid hormones regulate the speed of nearly every process in your body, including the hair growth cycle. When levels are off, follicles can prematurely enter the resting phase.
Excess androgens are another hormonal cause. Conditions like polycystic ovary syndrome (PCOS) raise androgen levels, which can trigger a different pattern of loss: gradual thinning concentrated at the crown and part line rather than diffuse shedding all over. This is female pattern hair loss, and unlike telogen effluvium, it involves follicle miniaturization. Over time, thick terminal hairs are replaced by finer, shorter ones. The distinction matters because female pattern hair loss is progressive and requires different management than temporary shedding.
Medications That Cause Shedding
Several common medications can trigger hair loss as a side effect. The shedding typically follows the same two-to-three-month delay as other forms of telogen effluvium, which makes it easy to miss the connection. Medications known to cause shedding include:
- Birth control pills, particularly when starting, stopping, or switching formulations
- Blood pressure medications like beta-blockers
- Blood thinners such as warfarin and heparin
- Mood stabilizers like lithium
- Seizure medications such as valproic acid
- High-dose vitamin A supplements or acne treatments derived from vitamin A
- Stimulant medications like amphetamines
If your shedding started a few months after beginning a new medication, that timing is worth noting when you talk to your doctor.
COVID-19 and Illness-Related Shedding
High fevers and significant infections are classic triggers for telogen effluvium, and COVID-19 proved to be an especially potent one. Hair shedding after COVID typically begins about two months after infection, with one study pinpointing onset at around 56 days. The shedding usually lasts three to six months before hair starts regrowing on its own. Surgery, hospitalization, rapid weight loss, and other major physical stressors follow a similar pattern.
Telling Temporary Shedding From Progressive Thinning
The most important distinction is between telogen effluvium (temporary, diffuse shedding) and female pattern hair loss (gradual, progressive thinning). They can look similar in early stages, and some women have both at the same time.
Telogen effluvium tends to come on suddenly, affects the entire scalp fairly evenly, and resolves once the trigger is removed. Female pattern hair loss develops slowly, concentrates along the center part and crown, and involves individual hairs becoming progressively finer over months or years. A dermatologist can distinguish between the two by examining hair diameter variation across your scalp. In female pattern hair loss, there’s significant variation in hair thickness, with a high percentage of fine, miniaturized hairs, especially at the front of the scalp. In telogen effluvium, the hairs that remain are mostly uniform in diameter.
Blood Tests Worth Requesting
If your shedding has lasted more than a couple of months without an obvious trigger, a few targeted blood tests can help identify or rule out the most common medical causes. A useful starting panel includes ferritin (not just a standard iron panel), thyroid-stimulating hormone (TSH), and androgen levels. Ferritin is the most frequently revealing result, since levels can be technically “in range” but still too low for your hair. A vitamin D check is also reasonable, as deficiency is common and has been linked to hair loss in some studies.
How Long Recovery Takes
Once the underlying cause is identified and addressed, most cases of telogen effluvium resolve within six to eight months. That timeline can feel slow because hair grows only about half an inch per month, so even after shedding stops, it takes several more months for regrowth to become noticeable. You’ll likely see short new hairs sprouting along your hairline and part before you notice overall density improving.
The most important factor in recovery is identifying and correcting the trigger. If the cause is stress, the shedding won’t fully resolve until cortisol levels come down. If it’s low ferritin, supplementation needs time to rebuild your stores. If it’s a medication, your doctor can discuss alternatives. For postpartum shedding and post-illness shedding, the timeline is largely fixed, and the hair recovers on its own without intervention.