DHT

DHT, or dihydrotestosterone, is the androgen that drives male pattern hair loss. An enzyme converts testosterone into it, and susceptible scalp follicles shrink in response.

Where you'll meet it

In every explanation of why finasteride works, and in the marketing for a great many shampoos, supplements and serums that claim to block it and mostly do not. It is the one piece of biology worth understanding properly, because almost every treatment claim in this field is a claim about DHT.

What does DHT do to hair?

DHT shrinks genetically susceptible follicles over repeated hair cycles. The enzyme 5-alpha reductase converts testosterone into DHT, DHT binds to androgen receptors in the follicle, and in follicles that are programmed to respond, each new hair comes in a little finer and shorter than the last. That process is miniaturisation, and it is what androgenetic alopecia actually is.

The same hormone does other jobs. It drives beard and body hair growth, which is why the beard tends to thicken while the hairline recedes, and it plays a part in prostate growth, which is why finasteride was first a prostate drug.

Why does it not affect the back of the head?

Because susceptibility is local, not systemic. Follicles at the hairline and crown respond to DHT; follicles in the donor area at the back and sides largely do not, even though they are bathed in the same hormone. They keep that resistance when they are moved, which is the single fact that makes a transplant work at all.

Is having too much DHT the problem?

Usually not. Men going bald generally have ordinary hormone levels, and blood testosterone or DHT results say very little about whether you will lose your hair. What varies is how sensitive the follicles are, and that sensitivity is inherited, from both sides of the family rather than only your mother's father. Testing your hormones to predict hair loss is not something most dermatologists would recommend.

What actually blocks it?

Finasteride blocks one form of 5-alpha reductase and lowers scalp DHT substantially. Dutasteride blocks more forms and lowers it further, and is usually a second-line option. Topical finasteride aims to lower scalp DHT with less reaching the rest of the body. All of these are prescription drugs and all need a proper conversation about side effects with whoever prescribes them.

Nothing over the counter has been shown to lower DHT enough to hold hair in the way finasteride does. Saw palmetto is the usual claim, and the evidence is much weaker and the products are not standardised. Ketoconazole shampoo has a possible mild local effect and is a reasonable extra, not a substitute. Minoxidil does not touch DHT at all; it works on the follicle instead, which is why it pairs well with finasteride rather than competing with it.

When a product claims to block DHT, the useful question is by how much, measured how. If the answer is a mechanism rather than a result, it is marketing. PRP and the rest goes through the common ones.

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