Losing between 50 and 100 hairs a day is completely normal. Your hair follicles cycle through growth and rest phases continuously, so a certain amount of shedding is just part of the process. If you’re finding clumps in the shower drain, noticing your ponytail getting thinner, or seeing more scalp than usual, something may be pushing more of your hair into its resting phase at once, or your follicles themselves may be shrinking over time. The cause is almost always one of a handful of common triggers.
Stress, Illness, and Sudden Shedding
The most common reason for a sudden increase in hair loss is a condition called telogen effluvium. Normally, about 10% of your hair is in the resting (telogen) phase at any given time. When your body goes through a major stressor, that percentage can spike dramatically, and all those resting hairs fall out around the same time.
The tricky part is the delay. Hair shedding typically starts two to three months after the triggering event, which makes it hard to connect the dots. You might have recovered from a bad illness, a surgery, a crash diet, or an intensely stressful period months ago and only now be watching your hair come out in handfuls. Common triggers include high fevers, significant weight loss, emotional trauma, stopping birth control, and major infections. COVID-19 became a well-known trigger during the pandemic.
The good news: acute telogen effluvium usually resolves on its own within six months. Your follicles aren’t damaged. They’re just temporarily resting, and once the trigger passes, they cycle back into growth.
Postpartum Hair Loss
If you recently had a baby, the shedding you’re seeing has a specific explanation. During pregnancy, elevated hormones keep more hair in its growth phase than usual, which is why many people notice thicker hair while pregnant. After delivery, those hormone levels drop, and all the hair that was “held back” enters the resting phase at once. The result feels dramatic.
Postpartum shedding usually starts about three months after giving birth and resolves between 6 and 12 months postpartum. It can look alarming, but it’s your hair returning to its pre-pregnancy baseline, not a sign of permanent loss.
Low Iron and Nutritional Gaps
Iron deficiency is one of the most overlooked causes of hair loss, particularly in women. Your hair follicles need a steady supply of nutrients to sustain their growth cycle, and iron is near the top of that list. In one study, women with excessive shedding had average ferritin levels (the protein that stores iron in your body) of about 16 ng/mL, compared to 60 ng/mL in women without hair loss. That’s a striking gap.
You don’t have to be fully anemic for low iron to affect your hair. If your ferritin drops below about 40 ng/mL and you’re also experiencing fatigue, paleness, or shortness of breath with exercise, iron supplementation is typically recommended. That said, whether iron supplements alone can restore hair density isn’t fully settled. They address the deficiency, but regrowth depends on how long the shedding has been going on and whether other factors are involved.
Vitamin D also plays a role in keeping follicles in their active growth phase. Research shows that the active form of vitamin D helps stimulate the cells at the base of the hair follicle and can prolong the growth cycle. If you spend little time outdoors, live in a northern climate, or have darker skin, a vitamin D deficiency is worth investigating.
Thyroid Problems
Both an overactive and an underactive thyroid can cause widespread hair shedding. Your thyroid hormones regulate metabolism throughout your body, including in hair follicles. When production is too high or too low, follicles can stop growing and enter their resting phase prematurely.
Thyroid-related hair loss tends to be diffuse, meaning it thins evenly across your scalp rather than in patches. It often comes alongside other symptoms: unexplained weight changes, fatigue, feeling unusually cold or warm, or changes in your skin. A simple blood test can check your thyroid function, and once levels are corrected with treatment, hair growth typically resumes within several months.
Genetic Hair Thinning
If your hair loss has been gradual rather than sudden, genetics may be the primary driver. Androgenetic alopecia, commonly called male- or female-pattern hair loss, affects both sexes and becomes more noticeable with age. It’s driven by a hormone called DHT, which is converted from testosterone in your body.
What DHT does is shrink hair follicles over time through a process called miniaturization. Your follicles don’t disappear all at once. The smaller, secondary hairs in each follicular group thin out first, which is why you notice reduced density before you see actual bald spots. Eventually, if the process continues, even the primary hairs miniaturize. Once a follicle loses its structural connection to the tiny muscle that helps anchor it, the loss becomes irreversible. The muscle tissue gets replaced by fat cells, and the follicle can no longer produce a visible hair.
In men, this typically shows up as a receding hairline and thinning at the crown. In women, it usually appears as a widening part or overall thinning on top, with the hairline staying intact.
Hormonal Conditions Like PCOS
Polycystic ovary syndrome is a common hormonal condition in women that can cause hair thinning through the same DHT-driven mechanism as genetic hair loss. PCOS raises androgen levels, which accelerates follicle miniaturization. Hair loss from PCOS rarely occurs in isolation. It’s usually accompanied by irregular periods, excess facial or body hair growth, or acne.
Treatment for PCOS-related hair loss often involves reducing androgen activity. Certain oral contraceptives work by suppressing the pituitary hormones that tell the ovaries to produce androgens, while also increasing a protein called sex hormone-binding globulin that soaks up circulating testosterone before it can convert to DHT.
How to Tell If Your Shedding Is Abnormal
Counting individual hairs isn’t practical, but there are signals worth paying attention to. If you’re consistently pulling out clumps when you wash or brush, if your part looks wider than it used to, or if you can see more scalp in photos, you’ve likely crossed beyond normal shedding.
Dermatologists use a simple test as a starting point: grasping a small section of hair and pulling firmly. Normally, zero to two resting hairs come out. If more than that release easily, it suggests active excessive shedding. If growing-phase hairs come out (identifiable by their tapered, pointed ends rather than rounded bulbs), that points to a different, more concerning process affecting the follicle itself.
What Actually Helps
The right approach depends entirely on the cause. For telogen effluvium triggered by stress, illness, or a nutritional gap, the priority is removing the trigger. Replenish iron or vitamin D if levels are low. Manage the underlying stress. Give it time. Most people see recovery within six to twelve months.
For genetic hair thinning, the over-the-counter treatment with the most evidence behind it is topical minoxidil (commonly sold as Rogaine). In a year-long study of over 900 users, 62% saw their affected area shrink, and about 64% rated the treatment as effective or very effective. Roughly 16% found it ineffective. Minoxidil works by extending the growth phase of the hair cycle and increasing blood flow to follicles, but it requires consistent, ongoing use. Stopping it typically means losing whatever ground you gained.
For hormonal causes like thyroid dysfunction or PCOS, treating the underlying condition is the most direct path to restoring hair growth. A blood panel checking thyroid hormones, ferritin, vitamin D, and androgens can clarify what’s going on and point toward the right solution.