Hair loss has dozens of possible causes, and the reason yours is happening depends on the pattern, the timing, and what else is going on in your body. Losing between 50 and 150 hairs a day is completely normal. If you’re finding clumps in the shower, noticing your part getting wider, or seeing patches of bare scalp, something beyond ordinary shedding is likely at play.
Stress-Related Shedding
One of the most common causes of sudden hair loss is a condition called telogen effluvium, where a large number of hair follicles shift into their resting phase all at once. The tricky part is timing: the shedding typically starts two to three months after the triggering event, so by the time your hair falls out, you may have forgotten what caused it.
Triggers include high fever, severe illness, major surgery, childbirth, significant psychological stress, and crash diets low in protein. Certain medications can also push hair into the resting phase, including some blood pressure medications, mood stabilizers, anti-inflammatory drugs, and acne treatments. Valproic acid, a common seizure and mood medication, causes hair loss in roughly 11% of people who take it. High-dose antifungal medications used for serious infections can trigger shedding within about three months of starting treatment.
The good news is that this type of shedding is almost always temporary. Acute telogen effluvium resolves within six months once the trigger is removed. If you recently stopped birth control pills, went through a stressful period, or recovered from a serious illness, this is a likely explanation.
Pattern Hair Loss and Genetics
If your hair is gradually thinning on top of your head or your hairline is receding, the most likely cause is androgenetic alopecia, the medical term for genetic pattern hair loss. It affects both men and women, though the pattern differs. Men tend to lose hair at the temples and crown. Women usually notice diffuse thinning along the part line.
The mechanism involves a hormone called DHT, which your body makes from testosterone. In people genetically predisposed to pattern hair loss, DHT shrinks the hair follicles over time and shortens each growth cycle. Hairs become finer and shorter with every cycle until some follicles stop producing visible hair altogether. This process is gradual, often unfolding over years or decades.
Two treatments have long been approved for this type of loss. Minoxidil is a topical solution (also available in low-dose oral form) that helps extend the growth phase of hair. Finasteride is an oral medication for men that blocks the conversion of testosterone to DHT. Both work best when started early and used consistently, and hair loss typically resumes if you stop them.
Hormonal Imbalances
Your thyroid gland plays a direct role in hair growth. Thyroid hormones stimulate the cells that build the hair shaft, reduce signals that tell hair to stop growing, and even help maintain hair color. When your thyroid is underactive or overactive, these processes slow down, and hair can become thin, dry, and prone to falling out. A simple blood test for thyroid-stimulating hormone (TSH) can screen for this.
In women, polycystic ovary syndrome (PCOS) is another common hormonal cause. PCOS raises levels of androgens, the same class of hormones responsible for pattern hair loss in men. Women with PCOS may notice thinning at the crown along with irregular periods, acne, or unwanted facial hair. Blood tests measuring testosterone and related hormones can help confirm the diagnosis.
Iron and Nutritional Deficiencies
Low iron is one of the most underrecognized causes of hair loss, especially in women who menstruate. Here’s the catch: standard lab reference ranges consider ferritin (your stored iron) normal at levels as low as 10 to 15 ng/mL. But research suggests your ferritin needs to be above 70 ng/mL to reliably support a healthy hair growth cycle. Levels between 21 and 70 ng/mL may be technically “normal” on a lab report but still too low for your hair.
If your hair loss is diffuse rather than patchy, asking your doctor to check ferritin specifically (not just a basic iron panel) is worth doing. Other nutritional factors that matter include adequate protein, zinc, biotin, and vitamin D, though iron deficiency is by far the most common dietary culprit.
Autoimmune Hair Loss
If you’re losing hair in distinct round or oval patches rather than gradually thinning, alopecia areata is likely. This is an autoimmune condition where your immune system mistakenly attacks hair follicles, treating them like invaders. The patches can appear on the scalp, eyebrows, eyelashes, or anywhere on the body.
Dermatologists look for a few telltale signs: tiny black dots where broken hairs sit just inside the follicle, “exclamation point hairs” that are thicker at the tip than at the base, and white hairs regrowing in the affected patches. Some people also develop small dents or pitting on their fingernails that feel rough, like sandpaper.
Alopecia areata is unpredictable. Some people regrow hair spontaneously within months, while others experience recurring episodes. For severe cases, a newer class of medications called JAK inhibitors has become available. Three are now FDA-approved for severe alopecia areata, offering a meaningful option for people who previously had very few treatments.
Hairstyle and Scalp Damage
Traction alopecia happens when hairstyles that pull on the hair are worn repeatedly over time. Tight braids, cornrows, high ponytails, buns, and styles secured with bobby pins can all cause it. The loss typically appears along the hairline or wherever the tension is greatest. Athletes who pull their hair back tightly and anyone who wears a turban, headwrap, or traditional upstyle for extended periods can be affected.
Early traction alopecia is reversible if you change your styling habits. But if the pulling continues long enough, the follicles scar over and the loss becomes permanent. Chemical straighteners can compound the damage. If you notice thinning along your hairline or temples and you regularly wear tight styles, loosening the tension is the single most important step.
Scalp Conditions That Cause Shedding
An inflamed, flaky scalp can contribute to hair loss, though it’s usually temporary. Seborrheic dermatitis, the condition behind persistent dandruff, is driven by an overgrowth of a yeast that naturally lives on skin. The yeast breaks down oils on the scalp into fatty acids that irritate the skin, causing redness, itching, and flaking. The hair loss comes mostly from scratching and chronic inflammation rather than direct damage to the follicle, so treating the underlying scalp condition typically allows hair to recover.
How to Figure Out Your Cause
Pay attention to the pattern and timeline. Diffuse thinning all over the scalp points toward telogen effluvium, nutritional deficiency, or thyroid problems. Gradual thinning at the crown or hairline suggests genetic pattern loss. Distinct bare patches suggest alopecia areata. Loss concentrated where hairstyles pull tightest points to traction.
Think back two to three months before the shedding started. Did you have surgery, a high fever, a major life stressor, or start a new medication? That delay between trigger and hair loss trips up a lot of people because the connection isn’t obvious.
A dermatologist can examine your scalp, pull gently on hairs to assess how easily they come out, and order blood work to check thyroid function, iron stores, and hormone levels. In some cases, a small scalp biopsy clarifies the diagnosis. Getting the right answer matters because the treatments are very different depending on the cause, and some forms of hair loss respond best when caught early.