Thyroid-related hair loss is diffuse and spread across the entire scalp rather than concentrated in one spot. Instead of a receding hairline or a bald patch, you’ll notice your hair looks uniformly thinner, with more scalp visible everywhere. The hair itself also changes, becoming dry, coarse, and brittle in ways that often show up before the thinning becomes obvious.
The Overall Pattern: Diffuse Thinning
The hallmark of thyroid hair loss is that it doesn’t follow the patterns most people associate with balding. There’s no receding at the temples, no widening part line on one side, and no circular bald spot on the crown. Both hypothyroidism and hyperthyroidism cause hair to thin evenly across the scalp, making it look uniformly sparse. You might first notice it as a smaller ponytail, more hair in the drain, or a general sense that your hair has lost its volume.
This diffuse pattern happens because thyroid hormones affect every hair follicle on your body, not just a localized group. When levels are too low or too high, follicles across the scalp shift out of their active growth phase prematurely and enter a resting phase. Months later, those resting hairs fall out roughly all at once. The result is a widespread shedding rather than a focused area of loss.
How the Hair Itself Changes
Before you notice thinning, you may notice your hair simply looks and feels different. Hypothyroidism in particular causes hair to become coarse, dull, dry, and brittle. Individual strands break easily, and the hair loses its natural shine. It may also grow more slowly than it used to, so new growth doesn’t keep pace with what’s falling out.
These texture changes happen because thyroid hormones drive the energy metabolism inside hair follicle cells. When hormone levels drop, follicle cells can’t produce strong, well-formed hair shafts. The strands that do grow are thinner, rougher, and more fragile. If you’re pulling broken hairs off your clothes or finding short, snapped pieces on your pillow, that’s a texture change worth paying attention to, especially combined with other hypothyroid symptoms like fatigue, weight gain, or dry skin.
Beyond the Scalp: Eyebrows and Body Hair
One of the most distinctive clues that hair loss is thyroid-related is that it doesn’t stop at the scalp. Unlike pattern baldness or stress-related shedding, thyroid dysfunction can thin your eyebrows, eyelashes, pubic hair, and armpit hair.
The eyebrow change is especially telling. People with significant hypothyroidism sometimes lose the outer third of their eyebrows, a finding sometimes called the Queen Anne sign. It’s not present in everyone with an underactive thyroid, but when it shows up alongside thinning scalp hair and dry skin, it points strongly toward a thyroid problem. If you’ve noticed that the tails of your eyebrows seem to have disappeared while the inner portions remain full, that’s a pattern worth mentioning to your doctor.
Scalp Changes That Come With It
The scalp itself often looks different too. Hypothyroidism causes excessively dry, scaly skin throughout the body, and the scalp is no exception. You might notice persistent flaking that doesn’t respond to dandruff shampoo, or a tight, itchy feeling on the scalp. This dryness isn’t the cause of the hair loss, but it’s part of the same underlying problem: thyroid hormones regulate skin cell turnover and oil production, so when levels are off, both your skin and hair suffer together.
Thyroid Hair Loss vs. Patchy Bald Spots
If you’re seeing distinct, circular bald patches rather than overall thinning, that’s a different condition called alopecia areata. Here’s where it gets complicated: alopecia areata and thyroid disease frequently overlap. Between 8% and 28% of people with alopecia areata also have a thyroid condition, and over 42% carry thyroid-related antibodies. The autoimmune process behind Hashimoto’s thyroiditis (the most common cause of hypothyroidism) can also trigger the immune system to attack individual hair follicles, creating those round, smooth patches.
So if you have autoimmune thyroid disease and develop circular bald spots, that’s likely alopecia areata occurring alongside your thyroid condition rather than the thyroid itself causing the loss. The two require different approaches, and distinguishing between them matters for treatment.
Hypothyroidism vs. Hyperthyroidism
Both underactive and overactive thyroid can cause diffuse hair loss, but the texture clues differ. Hypothyroidism produces the classic dry, coarse, brittle hair that breaks easily and looks dull. Hyperthyroidism tends to cause hair that’s finer and softer than usual, thinning without the same rough texture. In both cases the overall pattern is the same, with uniform thinning across the scalp, but running your fingers through your hair may tell you which direction your thyroid is off.
What Regrowth Looks Like
Once thyroid levels are brought back to normal with treatment, shedding typically slows within six to eight months. Regrowth takes time after that, and the first new hairs may come in with a slightly different texture before eventually returning to normal. Some people experience full regrowth, while others find their hair doesn’t completely return to its previous thickness, particularly if the thyroid condition went untreated for a long time.
It’s also worth knowing that thyroid medication itself can temporarily increase hair shedding when you first start it or change doses. This usually resolves on its own as your body adjusts and shouldn’t be confused with worsening disease. The key marker of progress is whether the hair that does grow back feels healthier, stronger, and less brittle than what you were losing.