Losing between 50 and 150 hairs a day is completely normal. If you’re suddenly pulling clumps from your brush, finding hair all over your pillow, or noticing your ponytail feels thinner, something has likely shifted your hair growth cycle. The cause is almost always identifiable, and most types of excessive shedding are reversible once you address the underlying trigger.
How to Tell If Your Shedding Is Excessive
Your hair goes through three phases: growing, transitioning, and resting. At any given time, about 85 to 90 percent of your hair is in the active growing phase, which lasts two to six years. The rest is in the resting phase, which lasts two to four months before those hairs fall out and new ones take their place. That natural turnover accounts for the 50 to 150 hairs you lose daily.
When something disrupts this cycle, a much larger percentage of your hair gets pushed into the resting phase all at once. Instead of the usual 10 to 15 percent, up to 70 percent of your growing hairs can shift into rest mode. A few months later, they all fall out together, and you notice dramatic shedding. Dermatologists can confirm this with a simple pull test: gently tugging a small section of hair. In people without active shedding, two hairs or fewer come out. If significantly more release, something is driving the loss.
Stress and Illness: The Most Common Trigger
The single most frequent cause of sudden, diffuse hair loss is a condition called telogen effluvium. It happens when a physical or emotional stressor pushes a large wave of hair follicles into the resting phase simultaneously. The tricky part is timing: the shedding doesn’t start until two to three months after the triggering event, so by the time your hair starts falling out, you may have forgotten what caused it.
Common triggers include high fevers, surgery, significant weight loss (especially crash dieting), severe emotional stress, and serious illness. COVID infections became a well-known trigger in recent years. Acute episodes typically resolve on their own within six months as new hair grows in behind the shed hairs. If the underlying stressor is ongoing, though, the shedding can become chronic.
Nutritional Deficiencies That Starve Your Follicles
Your hair follicles are among the fastest-dividing cells in your body, which makes them sensitive to nutritional shortfalls. Two deficiencies stand out as especially common culprits: iron and vitamin D.
Iron is the one most often missed. Standard lab work may flag your iron storage protein (ferritin) as “normal” at 15 to 30 ng/mL, but hair specialists consider anything below 30 highly likely to contribute to hair loss. The range associated with healthy hair growth starts around 40 to 70 ng/mL, with optimal results above 70 ng/mL. If you’re a menstruating woman, a vegetarian, or a frequent blood donor, your ferritin may be technically “normal” but far too low for your hair.
Low vitamin D is also consistently linked to hair loss. People experiencing shedding tend to have lower vitamin D levels than those who aren’t, though the exact threshold varies by individual. A simple blood test can check both levels, and correcting a deficiency often slows or stops the shedding within a few months.
Hormonal Changes
Thyroid Problems
Both an overactive and an underactive thyroid can cause hair to stop growing and eventually fall out. Thyroid hormones regulate metabolism in every cell, including hair follicles, so when production is too high or too low, follicles enter the resting phase prematurely. The shedding tends to be diffuse, meaning it thins evenly across your scalp rather than in patches. If you’re also experiencing unexplained weight changes, fatigue, feeling unusually cold or hot, or changes in your heart rate, a thyroid panel is worth requesting.
Postpartum Shedding
During pregnancy, elevated estrogen keeps hair in the growing phase longer than usual, which is why many pregnant women enjoy thicker hair. After delivery, those hormone levels plummet, and all the hair that was “held in place” sheds at once. This typically starts about three months after giving birth and resolves on its own within 6 to 12 months. It can look alarming, but it’s your hair returning to its pre-pregnancy baseline, not permanent loss.
PCOS and Androgen-Related Thinning
Conditions that raise androgen levels, like polycystic ovary syndrome, can cause a pattern of thinning that’s concentrated at the crown and along the part line. The mechanism is the same one behind genetic pattern hair loss: a hormone called DHT binds to receptors on genetically sensitive follicles, causing them to shrink over successive growth cycles. Each new hair grows in finer and shorter until the follicle produces only tiny, nearly invisible hairs.
Genetic Pattern Hair Loss
Androgenetic alopecia is the most common form of permanent hair loss, affecting both men and women. It’s driven by a genetic sensitivity to DHT, a hormone derived from testosterone. DHT shortens the growth phase and physically miniaturizes the follicle, so hairs become progressively thinner and weaker over time. In men, this typically shows up as a receding hairline and thinning crown. In women, it usually appears as a widening part and overall thinning on top, with the hairline staying intact.
Because this type of loss is gradual, many people don’t notice it until they’ve lost a significant amount of density. A 10-year study of over 500 men using a prescription DHT-blocking medication found that 91.5 percent showed improvement and 99.1 percent at least stopped progressing further. Over-the-counter topical treatments that stimulate blood flow to follicles are also effective for both men and women. The key with genetic thinning is that earlier treatment preserves more hair, since miniaturized follicles are harder to revive than ones that have only recently started shrinking.
Alopecia Areata: Patchy, Sudden Loss
If your hair is falling out in distinct round or oval patches roughly the size of a coin, you may be dealing with alopecia areata, an autoimmune condition where your immune system mistakenly attacks hair follicles. A telltale sign is “exclamation point” hairs around the edges of bare patches: short, broken hairs that are narrower at the base than the tip. Some people also develop tiny dents or pits in their fingernails.
This is the most common type of hair loss in patches. It can affect the scalp, beard, eyebrows, or eyelashes. Most people with the patchy form see regrowth within months, though the condition can recur. In rare cases, it progresses to total scalp or body hair loss. Treatment options have expanded significantly in recent years, and a dermatologist can help determine the best approach based on the extent of the loss.
Medications That Cause Shedding
A surprisingly long list of common medications can trigger hair loss as a side effect. Chemotherapy is the most well-known, but many everyday prescriptions are also culprits. These include blood thinners, beta-blockers (used for blood pressure and anxiety), birth control pills, seizure medications, lithium, gout medications, and even high-dose vitamin A supplements. Amphetamines prescribed for ADHD can also contribute.
Medication-related shedding usually follows the same delayed pattern as stress-related loss, appearing two to three months after starting the drug. If you’ve started a new medication in the past few months and notice increased shedding, that connection is worth discussing with your prescriber. In many cases, switching to an alternative medication resolves the problem.
What to Do Next
Start by thinking back two to three months. Did anything significant happen: an illness, a surgery, a major diet change, a new medication, childbirth? That delay between trigger and shedding is the most important clue. If nothing obvious comes to mind, or if the shedding has been gradual rather than sudden, a few targeted blood tests can reveal a lot. Ask for ferritin (not just a basic iron panel), vitamin D, and a thyroid panel. These three tests catch the most common correctable causes.
Pay attention to the pattern of your loss. Diffuse thinning all over points toward telogen effluvium, nutritional deficiency, or thyroid issues. Thinning concentrated along your part or at your crown suggests hormonal or genetic causes. Distinct bald patches suggest alopecia areata. Each pattern leads to a different treatment path, and most causes are treatable once correctly identified.