Hair loss from your thyroid: when TSH is the cause

A colleague of 38 came back from his GP with a TSH of 9.4 mU/l. He had spent three months on an expensive shampoo for his hair loss.

His hair was not going at the temples. It was thinning everywhere at once, and that is exactly the detail that matters.

I find it striking how few Dutch pages on this topic make that distinction. Most come from hair clinics, and they would rather sell a treatment than a blood test.

Can your thyroid cause hair loss?

Yes. Both an underactive and an overactive thyroid can go together with hair loss. Thyroid hormone helps set the pace at which your follicles move through their growth cycle. Disturb that rhythm and too many hairs shift to the resting phase at once, then shed in the same period.

What matters is that this is a minority of cases. Most men going bald have a perfectly fine thyroid.

With an underactive thyroid, hypothyroidism, hair loss also rarely stands alone. There is usually a package with it: tiredness, feeling cold, gaining weight without eating more, slow bowels, dry skin.

With an overactive thyroid the picture differs: palpitations, sweating, weight loss, restlessness. Hair can thin there too.

What both forms mean in men is covered in more depth in thyroid health in men.

How do you tell it apart from hereditary hair loss?

By the shape. Hereditary hair loss retreats in a pattern, at the temples and the crown, and leaves the rim at the back of your neck standing. Thyroid hair loss is diffuse: evenly thinner everywhere, without a clear shape, and often started within a few months. You see more hairs in the drain and on your pillow.

This is the table I use as a first split.

If you are unsure about your own pattern, look at the rim at your neck in a hand mirror. If it is joining in, it does not fit hereditary baldness. The whole pattern story is in hair loss in men.

Which thyroid values get measured?

Usually it starts with TSH. If that is off, free T4 follows to see how hard the thyroid itself is working. If an autoimmune cause is suspected, antibodies come next. The Dutch NHG guideline on thyroid disorders describes TSH as the first step with complaints that may point to thyroid problems.

What those numbers do, in plain language.

TSH works the opposite way to what you expect. A high TSH usually means a slow thyroid, because your brain is shouting louder for hormone that is not arriving.

We unpack that confusing detail calmly in TSH levels explained.

Can a hair supplement fake your TSH?

Less far-fetched than it sounds. Many hair supplements contain 5,000 to 10,000 micrograms of biotin. A large share of laboratory tests use biotin in the measuring reaction, and high doses can disturb the result. Thyroid assays are known to be sensitive to this.

It has been studied properly. Healthy adults taking 10 mg of biotin a day, a dose the researchers explicitly call common in over-the-counter supplements, went on to show abnormal hormone results (Li, 2017).

For thyroid hormones and TSH this has been mapped separately (Ylli, 2021). A review in Endocrine Reviews counts biotin among the interferences to consider when a thyroid result looks odd (Favresse, 2018).

Picture two men who both come back with a TSH of 4.8 mU/l.

One takes nothing and may have a mildly slow thyroid worth following. The other has been taking hair vitamins with 10 mg of biotin for three months, and for him that number may say more about his supplement than his thyroid.

That is the scenario I find most frustrating. You spend months chasing a thyroid problem you do not have.

So leave high-dose biotin for at least 48 hours before your blood draw. More on which supplements genuinely do something is in vitamins for hair loss.

Does hair grow back once your thyroid is right again?

Usually yes, but slowly. Hair follicles run a fixed cycle and it cannot be rushed. Count on three to six months before you see new growth, and six to twelve months for density to return. During that gap the shedding can even continue while your values are already normal.

That delay costs men their patience. They see a tidy TSH on paper, look in the mirror and conclude the treatment is not working.

Take the photo from above, every three months, in the same light. That is a fairer yardstick than your mood on a Tuesday morning.

If shedding continues while your thyroid has been fine for months, something else is probably involved. Then a conversation with your GP about iron, medication or inherited tendency is the logical next step.

What you can do now

Look at your pattern first, not at the amount of hair in your hand. Diffuse plus tired and cold is a reason to have your thyroid measured, receding temples without other complaints is not.

See your GP for bald patches, a red or flaking scalp, or hair loss that increased sharply within a few weeks.

If you want TSH, free T4 and your thyroid antibodies measured in one go, our thyroid function test covers them. If you take hair vitamins, leave them for two days before the draw.

Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.

References

1. Li D, Radulescu A, Shrestha RT, et al. Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA. 2017. PMID 28973622.
2. Ylli D, Soldin SJ, Stolze B, et al. Biotin interference in assays for thyroid hormones, thyrotropin and thyroglobulin. Thyroid. 2021. PMID 34042535.
3. Favresse J, Burlacu MC, Maiter D, Gruson D. Interferences with thyroid function immunoassays: clinical implications and detection algorithm. Endocr Rev. 2018. PMID 29982406.
4. Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The role of vitamins and minerals in hair loss: a review. Dermatol Ther (Heidelb). 2019. PMID 30547302.
5. Trost LB, Bergfeld WF, Calogeras E. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. J Am Acad Dermatol. 2006. PMID 16635664.