Hair loss in men: causes, stages and what your blood actually shows

My brother-in-law spotted it in a holiday photo. Not in the mirror, but in a shot taken from above on a terrace in Lisbon. He was 29.

By around age fifty, roughly half of men have visibly thinner hair. For plenty of them it starts well before thirty.

I spent an afternoon scrolling through the Dutch pages on this topic. Almost all of them are selling something: a transplant, a shampoo, a pill, a tub of vitamins.

What I could not find anywhere is the boring answer to the question men actually ask. Which part of this story sits in your blood, and which part does not?

Let me say it up front, even though I work for a company that sells blood tests. In most men, a blood test does not explain why they are going bald. That is exactly why it helps to know when it does add something.

What is the most common cause of hair loss in men?

By far the most hair loss in men is hereditary hair loss, also called androgenetic alopecia. Your hair follicles are sensitive to dihydrotestosterone, or DHT. Under its influence the hairs get shorter, thinner and lighter with every growth cycle, until they barely reach above the skin.

Note the word sensitive. That is the whole point.

It is not about how much DHT you have, but how your follicles respond to it. That sensitivity is largely inherited and spread across many genes, from both parents.

So the old story about your mother's father is only half right. There is truth in it, because the maternal line does contribute strongly, but your father's side counts too.

We have written up how that mechanism works in hair loss in men and DHT.

How do you recognise hereditary hair loss?

Hereditary hair loss follows a pattern. It starts at the temples and the crown, while the rim of hair at the back of your neck and above your ears stays put. Those follicles are naturally far less sensitive to DHT. Diffuse loss across your whole scalp does not fit this pattern.

Dermatologists use the Norwood scale for this, with seven stages. Stage 1 is a full hairline, stage 7 is a narrow band around the back of the head.

You do not need to memorise that scale. You do need the question underneath it: is my hairline receding into a shape, or is everything thinning evenly?

One practical trick. Take the same photo every three months, from above, in daylight, in the same bathroom. Your reflection is a poor judge, a series of photos is not.

And one more thing. You always lose hair. Fifty to a hundred hairs a day is normal, and in autumn that often runs a little higher.

When is hair loss not a hereditary matter?

If the hair thins across your whole scalp at once, and especially if it started suddenly, that does not fit the hereditary pattern. Doctors then think of diffuse hair shedding, called telogen effluvium. It usually shows up one to three months after a clear event: surgery, a high fever, sharp weight loss, a bereavement, a new medication.

This is the form that often recovers.

There is also alopecia areata, where round bald patches appear because the immune system attacks the follicles. Those patches are sharply bordered and smooth, very different from a receding hairline.

Medication can play a part too. Some blood pressure drugs, certain antidepressants and isotretinoin are known for hair loss as a side effect. Check the Farmacotherapeutisch Kompas or ask your pharmacist, and never stop on your own.

Thuisarts describes calmly and in plain language when to see your GP about hair loss. For bald patches, redness, flaking or an itchy scalp, that is where you belong anyway.

Which blood values say something about hair loss?

With hair loss, blood testing is not looking for the cause of baldness but for contributing factors you can act on. In practice that means your iron stores, your thyroid and a few vitamins. With the classic receding pattern those values usually add little, with diffuse loss they often do.

Here is what sits in such a panel and what each number does and does not do.

That last row is the most important, and the most ignored.

Men have their testosterone measured because they are going bald. It is logical thinking and still the wrong turn. Baldness is about how sensitive your follicles are, not about how high your testosterone runs in blood.

Two men can both sit at 18 nmol/l. One still has a full head at 45, the other is far along at 30. Same value, different follicles.

If you also have complaints like low energy, less interest in sex or harder muscle gain, then measuring testosterone is worthwhile after all. You are testing those complaints, not your hair. What gets measured is covered in low testosterone in men.

When does blood testing for hair loss make sense?

Briefly: when the pattern does not match hereditary hair loss, or when other complaints sit alongside it. With a slowly receding hairline and nothing else, testing rarely turns anything up. With sudden diffuse loss, or loss plus fatigue, cold intolerance or weight change, it is a different story.

This is the table I use as a first filter.

What matters to me here: a normal result is not a wasted result. If your ferritin and TSH are fine, you can cross those two off and put your energy into treatment instead of another tub of pills.

If you are unsure which values belong in it, we walk through them one by one in the hair loss blood test.

Can a vitamin deficiency cause hair loss?

Yes, but far less often than the supplement industry suggests. Iron deficiency and a marked shortage of vitamin D or B12 can go together with diffuse hair shedding. For healthy men without a deficiency there is little evidence that extra vitamins thicken hair. A review of vitamins and minerals in hair loss concluded that larger studies are still missing (Almohanna, 2019).

And here sits the most underrated trap in this whole subject.

Hair supplements often contain 5,000 to 10,000 micrograms of biotin. That is hundreds of times the daily need of around 40 micrograms that the Voedingscentrum works with.

Many laboratory tests use a technique in which biotin plays a starring role. Take high doses and the result can skew. In a JAMA study, healthy adults took 10 mg of biotin a day, explicitly described as a dose common in over-the-counter supplements, after which several hormone assays went off (Li, 2017).

Thyroid values are sensitive to this (Ylli, 2021). A skewed TSH or free T4 can look exactly like a thyroid problem you do not have.

Picture the scenario. You are going bald, you take hair vitamins for three months, you get blood drawn and your thyroid looks disturbed. The problem is not your thyroid but your tub of biotin.

So stop high-dose biotin at least 48 hours before a blood draw, and tell the lab or your doctor that you use it (Luong, 2019). Which deficiencies genuinely matter is covered in vitamins for hair loss.

Can stress cause hair loss?

Heavy stress can trigger diffuse shedding, usually one to three months after the period itself. We are talking about real blows: a hospital admission, a divorce, a burnout, a bereavement. Everyday work pressure is rarely enough. Hereditary hair loss is not caused by stress, though stress can temporarily make the picture worse.

The delay makes it confusing. Men tell me about hair loss in March and blame that month's workload, when January's flu was probably the trigger.

The good news is that this form usually recovers once the trigger is gone. Count on six months to a year before density returns.

What can you do about hair loss?

For hereditary hair loss there are two treatments with serious research behind them: minoxidil on the scalp and finasteride as a tablet. Both mainly slow further loss, and both work only while you use them. Stop, and within about a year you catch up to where you would have been untreated.

Most men find that last sentence the most annoying one in this article. It is still the most honest.

Minoxidil is available without prescription in the Netherlands. In randomised research the 5% solution produced more hair growth than 2% and than placebo (Olsen, 2002). We have written up the user side and the first months in minoxidil experiences.

Finasteride needs a prescription and blocks the conversion of testosterone to DHT. In a trial in men with hereditary hair loss, hair growth improved compared with placebo (Kaufman, 1998). It carries sexual side effects you should take seriously, and it lowers your PSA value sharply. What that means for prostate testing is in finasteride experiences.

If your thyroid is involved, the order is different. Then treating the thyroid comes first and the hair follows. That story is in hair loss and your thyroid.

What you can do now

Start with a photo from above in daylight, and put the date on it. Without that baseline you will not know in six months whether anything worked.

See your GP if you have bald patches, if your scalp is red or flaking, or if the loss started suddenly and across your whole head.

If you want to know whether your ferritin, thyroid and vitamins are playing a part, our extended health checkup covers those values in one go. If you take hair vitamins, leave them for at least 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. 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.
2. 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.
3. Ylli D, Soldin SJ, Stolze B, et al. Biotin interference in assays for thyroid hormones, thyrotropin and thyroglobulin. Thyroid. 2021. PMID 34042535.
4. Luong JHT, Male KB, Glennon JD. Biotin interference in immunoassays based on biotin-strept(avidin) chemistry: an emerging threat. Biotechnol Adv. 2019. PMID 30872068.
5. Olsen EA, Dunlap FE, Funicella T, et al. A randomized clinical trial of 5% topical minoxidil versus 2% topical minoxidil and placebo in the treatment of androgenetic alopecia in men. J Am Acad Dermatol. 2002. PMID 12196747.
6. Kaufman KD, Olsen EA, Whiting D, et al. Finasteride in the treatment of men with androgenetic alopecia. J Am Acad Dermatol. 1998. PMID 9777765.
7. 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.