Losing some hair every day is completely normal. Healthy adults shed between 50 and 150 hairs daily as part of the hair’s natural life cycle. But if you’re finding clumps in the shower drain, noticing your part getting wider, or seeing more scalp than usual, something beyond normal shedding is likely going on. The cause could be anything from stress to genetics to a vitamin deficiency, and figuring out which one matters because the fix is different for each.
How Hair Growth Normally Works
Your hair goes through a repeating cycle of growth, transition, and rest. The growth phase lasts about 2 to 8 years, which is why head hair can get so long compared to body hair. After that, the follicle enters a brief transition period of about two weeks, then shifts into a resting phase lasting 2 to 3 months. At the end of the resting phase, the hair falls out and a new one starts growing in its place. At any given time, roughly 9% of your scalp hairs are in that resting phase, quietly waiting to shed.
When something disrupts this cycle, either by pushing too many hairs into the resting phase at once or by shrinking the follicles themselves, you notice hair loss. The pattern and timing of the loss often point directly to the cause.
Genetics and Pattern Hair Loss
The most common reason for ongoing hair loss is inherited sensitivity to hormones called androgens. In this type of hair loss, a hormone called DHT gradually shrinks the base of certain hair follicles by reducing the number of cells that support each strand. Over time, follicles that once produced thick, visible hairs start producing thinner, shorter, nearly invisible ones. Each follicle has its own genetic susceptibility to this process, which is why some areas thin while others stay full.
In men, this typically shows up as a receding hairline and thinning at the crown. In women, it usually looks like overall thinning along the part line, without a receding hairline. If your parents or grandparents lost hair in a similar pattern, genetics is the most likely explanation. This type of loss is gradual, happening over years or decades, and it doesn’t reverse on its own.
Stress and Sudden Shedding
If your hair loss started suddenly and seems to come out in handfuls rather than in one specific spot, a condition called telogen effluvium is a strong possibility. A major physical or emotional stressor pushes a large percentage of your hair follicles into the resting phase all at once. The tricky part is the delay: hair typically starts falling out two to three months after the triggering event, so by the time you notice the shedding, you may have forgotten what caused it.
Common triggers include surgery, high fevers, significant weight loss, childbirth, emotional trauma, and severe illness. The good news is that acute telogen effluvium usually resolves on its own within six months once the stressor passes. Your hair cycles back to normal and regrows without treatment. If the shedding continues beyond six months, the underlying trigger may still be active, whether that’s ongoing stress, a nutritional gap, or an undiagnosed medical issue.
Nutritional Deficiencies
Your hair follicles need a steady supply of nutrients to sustain growth, and low iron is one of the best-studied deficiency links to hair loss. Research has found that women with pattern hair loss had average iron storage levels (measured by a protein called ferritin) of about 37 ng/mL, compared to roughly 60 ng/mL in women without hair loss. Women with patchy hair loss had even lower levels, around 25 ng/mL. You can be low in iron without being fully anemic, which means standard bloodwork might not flag it unless your doctor specifically checks ferritin.
Other nutritional factors that can contribute include low levels of vitamin D, zinc, and biotin, though iron deficiency has the strongest evidence behind it. Crash diets and very restrictive eating patterns are a particularly common culprit because they deplete multiple nutrients at once while also acting as a physical stressor that can trigger telogen effluvium on top of the deficiency.
Thyroid and Hormonal Imbalances
Both an overactive and underactive thyroid can cause diffuse hair thinning. If your hair loss comes alongside unexplained weight changes, fatigue, or sudden muscle weakness, a thyroid issue is worth investigating. A simple blood test measuring thyroid-stimulating hormone (TSH) can confirm or rule this out quickly.
In women, excess androgens from conditions like polycystic ovary syndrome (PCOS) can drive thinning that looks similar to genetic pattern loss but develops more rapidly. Other signs of elevated androgens include acne, irregular periods, and excess facial or body hair. Blood tests can measure androgen levels directly, helping distinguish hormonal thinning from purely genetic hair loss. The distinction matters because hormonal causes often respond to treating the underlying imbalance.
Medications That Cause Hair Loss
A surprisingly long list of common medications can trigger hair shedding as a side effect. Some of the most well-known include blood thinners like warfarin, beta-blockers used for heart conditions, birth control pills, certain antidepressants (including SSRIs like fluoxetine and sertraline), cholesterol-lowering drugs, acne medications based on vitamin A (like isotretinoin), hormone replacement therapy, and some anti-inflammatory painkillers like naproxen.
Medication-related hair loss typically follows the same two-to-three-month delay as stress-related shedding, which can make it hard to connect the timing to a new prescription. If you started a medication a few months before noticing increased shedding, it’s worth discussing with your prescriber. In most cases, hair regrows after the medication is stopped or changed, though some alternatives may work just as well for your condition without the hair loss side effect.
Alopecia Areata
If your hair is falling out in small, round patches roughly the size of a quarter, you may be dealing with alopecia areata, an autoimmune condition where your immune system mistakenly attacks hair follicles. One telltale sign is “exclamation point hairs,” short broken hairs that are thicker at the top and taper to a narrow point near the scalp. These are distinctive enough that a dermatologist can often identify the condition just by looking.
Alopecia areata is unpredictable. Some people lose a single patch that regrows within months. Others develop multiple patches, and in rare cases, lose all scalp hair or all body hair. Because the follicles aren’t permanently destroyed (at least early on), regrowth is possible, but the condition can recur. Treatment typically focuses on calming the immune response in the affected area.
Tight Hairstyles and Traction Alopecia
Hairstyles that pull on the hair, including tight ponytails, braids, buns, extensions, and weaves, can physically damage follicles over time. The loss shows up where the tension is greatest, usually along the hairline and temples. Early warning signs include soreness or redness on the scalp, small bumps around the hairline, and headaches from the pulling (sometimes called “ponytail headaches”).
Caught early, traction alopecia is reversible. Loosening your style and giving your hairline a break allows follicles to recover. But if the tension continues for years, the repeated damage can cause scarring that permanently destroys the follicles. At that point, the hair in those areas won’t come back. If your scalp feels sore or looks red and inflamed where you part or pull your hair, that’s a signal to change your routine now rather than later.
What Helps Hair Grow Back
Treatment depends entirely on the cause. For genetic pattern hair loss, topical minoxidil (available over the counter) is the most widely studied option. In clinical trials, the 5% concentration produced 45% more regrowth than the 2% version over 48 weeks. It works by extending the growth phase and increasing blood flow to follicles, but it requires consistent daily use. Stopping it means the hair loss resumes.
For stress-related or medication-related shedding, the primary treatment is removing the trigger. Once the stressor passes or the medication is changed, hair typically returns to its normal cycle within several months. Nutritional causes respond to correcting the deficiency, whether through diet changes or supplementation. Hormonal causes often improve when the underlying condition is treated. Alopecia areata may be treated with topical or injectable anti-inflammatory medications to suppress the localized immune response.
Getting the Right Diagnosis
Because so many conditions look similar on the surface, the right blood tests can save you months of guessing. The most useful panel typically includes ferritin (iron stores), TSH (thyroid function), and androgen levels, especially for women experiencing diffuse thinning without a clear trigger. A dermatologist can also examine the pattern of loss, check for exclamation point hairs or scarring, and sometimes perform a scalp biopsy if the cause isn’t obvious.
Pay attention to timing. Hair loss that started two to three months after a major life event, illness, or new medication points toward telogen effluvium. Gradual thinning in a predictable pattern over years suggests genetics. Sudden round patches suggest alopecia areata. And loss concentrated at the hairline in someone who wears tight styles points to traction. The pattern tells a story, and matching it to the right cause is the fastest path to getting your hair back.