If your hair is thinning, breaking, shedding more than usual, or just looks and feels different than it used to, the cause almost always falls into one of a handful of categories: nutritional gaps, hormonal shifts, stress, scalp conditions, or physical damage from styling. Most of these are fixable once you identify what’s actually going on. Here’s how to narrow it down.
You’re Losing More Hair Than Normal
Healthy hair goes through a growth cycle where most strands are actively growing at any given time, while a small percentage are resting and about to shed. Losing 50 to 100 hairs a day is completely normal. You’ll see them in the shower drain, on your pillow, in your brush. The problem starts when that number climbs noticeably, your ponytail feels thinner, or you can see more scalp than before.
First, figure out whether you’re dealing with shedding or breakage, because the fix is different. Shed hairs come out from the root and have a small white bulb at one end. Broken hairs snap off partway down the strand and look blunt or uneven at the tip, with no bulb attached. If your hair is all over the bathroom floor with little bulbs visible, your follicles are pushing hairs out early. If you’re finding short, uneven pieces and your hair feels rough or straw-like, the shaft itself is damaged.
Stress-Related Shedding
One of the most common causes of sudden, diffuse hair loss is a condition called telogen effluvium. It happens when a physical or emotional stressor pushes a large batch of hair follicles into their resting phase all at once. The tricky part is timing: the shedding typically shows up two to three months after the triggering event, so by the time you notice clumps in the shower, you may have forgotten what set it off.
Common triggers include surgery, high fever, significant weight loss, stopping or starting birth control, childbirth, and periods of intense emotional stress. The acute form lasts fewer than six months, and hair generally returns to normal on its own once your body recovers. If shedding continues beyond six months, something else may be keeping the cycle disrupted, whether that’s ongoing stress, a nutritional deficiency, or a thyroid issue.
Nutritional Deficiencies That Show Up in Your Hair
Your hair follicles are metabolically demanding. When your body is low on key nutrients, hair is one of the first things it deprioritizes. Iron is the biggest culprit, especially for women. Standard blood work might tell you you’re not anemic, but your iron stores can still be too low for healthy hair growth. Research published in the Tzu Chi Medical Journal found that hair needs serum ferritin levels of 40 to 60 ng/mL to grow properly, while the threshold for diagnosing anemia doesn’t kick in until ferritin drops much lower. In other words, you can have “normal” blood counts and still be iron-deficient enough to lose hair. Some researchers now suggest that ferritin should be at least 60 ng/mL for adequate hair health.
Biotin deficiency is another common finding. A study in the International Journal of Trichology found that 38% of women who came in complaining of hair loss had biotin levels consistent with deficiency. That said, biotin supplements have become enormously popular, and taking them when you’re not actually deficient won’t do much. The same goes for zinc, vitamin D, and protein. If your diet is very restricted, you’ve recently lost a lot of weight, or you have a digestive condition that affects absorption, a blood panel checking these levels is worth requesting.
Hormonal and Thyroid Changes
Hormones are the single biggest driver of long-term, progressive hair thinning. In women, the most common pattern is a gradual widening of the part line and thinning across the crown, while the frontal hairline stays mostly intact. This is classified in three stages: stage one is perceptible thinning on the crown starting about one to three centimeters behind the hairline, stage two is more pronounced thinning in that same zone, and stage three is near-complete loss across the crown. If you’re noticing your part getting wider over months or years rather than sudden shedding, this hormonal pattern is the likely explanation.
Thyroid problems can also dramatically change your hair. An underactive thyroid tends to make hair dry, coarse, and brittle, with a specific type of damage where the hair shaft develops weak points and snaps. An overactive thyroid causes thin, fragile hair and can trigger premature graying. Both can accelerate shedding. If your hair texture has changed alongside symptoms like fatigue, weight changes, feeling unusually cold or hot, or mood shifts, a thyroid panel is one of the first tests to consider.
Scalp Problems That Affect Growth
Your scalp is skin, and skin conditions directly affect the hair growing from it. The two most common issues are dandruff and seborrheic dermatitis, which exist on a spectrum but differ in important ways.
Dandruff stays on the scalp and shows up as light white or yellowish flakes scattered through your hair, with little to no redness. Itching ranges from absent to mild. Seborrheic dermatitis is more aggressive: it produces thicker, greasier scales, causes visible redness and inflammation, and can spread beyond the scalp to the eyebrows, the sides of the nose, behind the ears, and onto the upper chest. About 70% of adults with seborrheic dermatitis have scalp involvement, and 88% have facial involvement. Both conditions involve an overgrowth of a naturally occurring yeast on the skin, but seborrheic dermatitis involves a stronger inflammatory response.
If your scalp is persistently itchy, flaky, red, or has patches of scaling that don’t respond to over-the-counter dandruff shampoo, the inflammation itself can disrupt hair growth. Scarring conditions, where the scalp looks shiny, smooth, or discolored in patches where hair used to grow, are more serious. Hair lost to scarring typically doesn’t come back, which is why early evaluation matters.
Physical Damage and Breakage
Sometimes the issue isn’t your health at all. It’s what you’re doing to your hair. Heat styling, chemical treatments like relaxers and permanent color, tight hairstyles that pull on the same follicles repeatedly, and even aggressive brushing when hair is wet can all cause the shaft to weaken and snap. The result looks like thinning, but it’s actually breakage, and the follicles themselves are fine.
Signs of mechanical damage include short, flyaway hairs of varying lengths (especially around the hairline and temples), split ends, a rough or straw-like texture, and hair that feels stretchy when wet but snaps instead of bouncing back. If you’ve recently bleached, colored, or chemically straightened your hair and it suddenly feels different, the damage is structural. The good news is that follicles are still producing hair normally. The bad news is that damaged lengths can’t be repaired, only grown out.
What About Hard Water?
Hard water, meaning water with high concentrations of calcium and magnesium, is often blamed for hair problems. The reality is more nuanced than social media suggests. A study in the International Journal of Trichology compared hair washed in hard water versus distilled water and found no statistically significant difference in tensile strength or elasticity under normal washing conditions. That said, the researchers noted that very high mineral content or prolonged exposure over long periods could potentially change the results. If you’ve moved to a new area and your hair feels different, hard water might be contributing to buildup that makes hair look dull or feel stiff, but it’s unlikely to be the primary cause of significant shedding or thinning.
How to Figure Out Your Specific Cause
Start by looking at the pattern. Diffuse thinning all over, especially after a stressful event a few months ago, points toward telogen effluvium. A widening part that’s been getting gradually worse suggests hormonal thinning. Patchy bald spots, especially round smooth ones, suggest an autoimmune condition called alopecia areata. Breakage concentrated where you style, pull, or heat-treat your hair points to physical damage.
A dermatologist can do a simple pull test to assess whether you have active hair loss. They’ll grasp about 40 strands and gently tug. In healthy hair, two or fewer strands should come out per pull. If six or more come out, that confirms active shedding and warrants further investigation. Blood work for ferritin, thyroid hormones, vitamin D, and biotin can identify or rule out the most common internal causes.
Pay attention to what came before the hair change. New medication, a crash diet, a stressful few months, a baby, stopping birth control, a new styling routine. Hair problems are almost always a delayed signal from something that happened weeks or months earlier, and matching the timeline to the trigger is often the fastest route to an answer.