Can your thyroid thin your hair? Yes, whether it’s running too slow or too fast. An underactive thyroid (hypothyroidism) can leave hair dry and thin. An overactive one (hyperthyroidism) lists hair loss as a symptom too. Both are more common in women, and both are found with a blood test, not by staring at your hairbrush. The good news is that hair loss can reverse once the thyroid is treated. Thyroid medicine can play a part as well, which is covered below. If your hair is thinning and you feel off in other ways, ask your doctor to check your thyroid.
Too little vs. too much thyroid hormone
Your thyroid is the butterfly-shaped gland at the front of your neck. Its hormones help your whole body use energy. That’s why being off in either direction shows up in so many places at once, hair included.
| Detail | Underactive (hypothyroidism) | Overactive (hyperthyroidism) |
| What’s happening | The thyroid doesn’t make enough hormone, and the body slows down | The thyroid makes too much, and the body speeds up |
| Hair | Dry, thinning hair | Hair loss |
| Other common signs | Tiredness, feeling cold, weight gain, dry skin, constipation, heavy or irregular periods | Racing heart, sweating, feeling hot, shaky hands, weight loss, trouble sleeping, lighter or less frequent periods |
| Most common cause | Hashimoto’s disease, an autoimmune condition | Graves’ disease, also autoimmune |
| How common | Nearly 5 in 100 Americans 12 and older | About 1 in 100 Americans 12 and older |
The row that matters most is “other common signs.” Thinning hair by itself has a long list of possible causes. Thinning hair plus exhaustion, always feeling cold and a heavier period is a different story. So is thinning hair plus a pounding heart and weight dropping off without trying.
The underactive side: slow and easy to miss
Hypothyroidism usually creeps in. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says it can come on so slowly that you don’t notice for months or even years. Many of its symptoms, like tiredness and weight gain, are common and don’t always mean a thyroid problem. Every symptom has an ordinary excuse.
Hashimoto’s disease, the most common cause, is 4 to 10 times more common in women than men. It most often starts between ages 30 and 50. The immune system attacks the thyroid until it can’t make enough hormone.
Other causes include thyroid surgery, radiation, a swollen, inflamed thyroid (thyroiditis), and some medicines, including lithium and amiodarone.
The overactive side: everything speeds up
Hyperthyroidism is less common, but its symptoms are hard to ignore. The American Thyroid Association lists sweating, a racing or uneven heartbeat, shaky hands and anxiety. There’s also weight loss even when you eat normally or more, frequent trips to the bathroom, trouble sleeping, and hair loss. Symptoms can start suddenly or slowly, and you may not have them all.
Causes include Graves’ disease, overactive lumps on the thyroid (nodules), thyroiditis, too much iodine, and too much thyroid medicine. That last one comes up again below.
After a baby, look twice
Shedding after a baby is normal. It usually starts around two months after birth, peaks around four months, and settles on its own. Our guide to postpartum hair shedding covers it in detail.
But the months after a baby are also when postpartum thyroiditis shows up. The American Thyroid Association puts it at about 5% to 10% of women in the US. It can start with an overactive phase 1 to 4 months after delivery. The anxiety, poor sleep, fast heartbeat and weight loss are easy to blame on a newborn. More women are diagnosed in the underactive phase, usually 4 to 8 months after delivery, with tiredness, weight gain, dry skin and low mood. Most get back to normal within 12 to 18 months. About 20% of those who go through the underactive phase stay hypothyroid.
So if shedding drags well past the usual window, or you feel worse as the months go on, get a blood test. Don’t settle for another round of “it’s just the baby.”
Can thyroid medicine cause hair loss?
It can, and the labels say so plainly.
Levothyroxine (Synthroid and its generics) is the standard daily pill for an underactive thyroid. Its label says partial hair loss may happen, rarely, in the first few months, and that it’s usually temporary. The label also says side effects mostly come from too high a dose, which acts like an overactive thyroid. Hair loss is on that list, next to a fast heartbeat, nervousness, feeling too hot and weight loss.
Methimazole, a common medicine for an overactive thyroid, lists unusual hair loss as one of its minor side effects.
None of this means the medicine is wrong for you. The American Thyroid Association says levels are usually rechecked 6 to 8 weeks after you start or change a dose. If you notice shedding after starting or changing thyroid medicine, tell your prescriber and let them check your numbers. Don’t stop or change it yourself. Our guide to medications that can cause hair shedding covers the bigger picture.
Getting checked
Symptoms alone can’t diagnose a thyroid problem, because so many overlap with other conditions. The usual first tests are TSH, the hormone that tells your thyroid to work, and free T4, the thyroid hormone your body actually uses. When the thyroid is underactive, TSH usually goes up.
If you’re trying to fix your hair, there’s one thing to know about biotin. The levothyroxine label warns that biotin supplements can throw off thyroid blood tests. It says to stop biotin at least 2 days before testing. If you take it, mention it when the test is ordered. Our biotin explainer covers whether it even helps hair.
If you see a dermatologist about thinning, they may test your thyroid along with iron and other levels. Low iron is another common cause that a test can catch, and our post on signs of iron deficiency explains it. Thyroid disease is also linked with alopecia areata, an immune condition that causes patchy hair loss. That’s one more reason a bald patch, not all-over thinning, deserves a dermatologist’s look.
Will it grow back?
The American Academy of Dermatology says treating thyroid disease can reverse the hair loss it causes. It takes patience. Hair grows slowly, and the levothyroxine label says a dose can take 4 to 6 weeks to fully kick in, before your hair even starts to catch up.
Gentle basics while you wait
None of these treat a thyroid problem or regrow hair. They cut down on breakage and help thinner hair look a little fuller while the real fix happens.
Prices move constantly, so we link to live listings instead of printing a number that is wrong by the time you read it. Links go to Amazon, which is where a referral gets credited.
CeraVe Gentle Hydrating Shampoo is about $9, though the price changes often. CeraVe says it’s free of sulfates, dyes, parabens and fragrance, made for all hair types including color-treated, with hyaluronic acid.
Paul Mitchell Detangler Comb is about $6. It’s a wide-tooth comb for wet or dry hair, and it’s kinder than a tight-bristled brush when every strand feels precious.
Kitsch Ultra-Petite Satin Scrunchies are about $9 for six. Kitsch says the satin helps cut down on breakage and doesn’t leave creases.
Toppik Hair Building Fibers are about $25 for 12 grams, in shades from black to white. You shake the colored fibers over a thin spot or part. Toppik says they stay put through wind, rain and sweat until you wash, and they don’t help or hurt growth. Our guide to hair shedding vs. hair loss helps you tell which one you have.
How we picked
Everything here is sold over the counter, and nothing claims to regrow hair or treat a thyroid problem. There’s a fragrance-free shampoo for dry hair, two gentle tools, and one cover-up. No supplements, because thyroid problems need a diagnosis and biotin can mess up the test.
When to ask for the test
If your hair is thinning and you’re also exhausted, cold and gaining weight, ask for a thyroid test. That’s exactly what it’s for.
If you’re shedding, your heart races and you’re losing weight without trying, see a doctor soon instead of waiting it out.
If you had a baby in the past year and things feel worse, not better, say “postpartum thyroiditis” out loud at your appointment. It’s common and easy to miss.
If you started levothyroxine recently and your hair is shedding, keep taking it and tell your prescriber. The label calls this rare and usually temporary, and your levels may just need a check.
If you take biotin for your hair, mention it before any thyroid blood work.
FAQ
What does thyroid hair loss look like?
Thinning, often with dry hair if your thyroid is underactive. Some people notice hair coming out in clumps when they brush.
Does Hashimoto’s cause hair loss?
Hashimoto’s is the most common cause of an underactive thyroid, and dry, thinning hair is one of the symptoms.
Can thyroid hair loss be reversed?
Often, yes, once the thyroid problem is treated. Give it months.
Can my thyroid be normal and my hair still thin?
Yes. Low iron, stress, a recent illness, pregnancy, medicines and genes are all common causes. That’s why testing beats guessing.
Bottom line
Your thyroid can thin your hair whether it runs slow or fast. Treat the thyroid, and hair can recover. Get the blood test, tell your doctor about biotin, and be gentle with your hair in the meantime. More is in our hair archive.
