For many people with pattern hair loss, the explanation eventually comes down to a single hormone: dihydrotestosterone, or DHT. It is a big part of the reason two people with similar testosterone levels can have very different hair, and it is also why a prescription medication like finasteride can meaningfully change the course of hair thinning for some people without changing testosterone itself. Understanding what DHT is, how it affects hair follicles, and where treatments step into that process makes it much easier to understand why a clinician might recommend one option over another.
This guide walks through what DHT is, how it is made, why it affects some hair follicles and not others, and how finasteride and other options fit into the picture.
This article is patient education, not medical advice. It does not create a doctor-patient relationship and is not a substitute for an individualized evaluation from a licensed clinician. For a broader look at how this process shows up over time, see our guide to male pattern hair loss.
What DHT is
Dihydrotestosterone, or DHT, is a hormone made from testosterone by an enzyme called 5-alpha reductase. Dihydrotestosterone (DHT) is a hormone made from testosterone by the enzyme 5-alpha reductase, and the conversion happens throughout the body rather than in a single organ. DHT itself has several normal, necessary roles: it contributes to the development of male genitalia before birth, and later in life it influences body and facial hair growth, oil production in some skin areas, and the prostate gland. DHT is not an inherently harmful hormone; it simply interacts differently with different tissues.
The relevant detail for hair loss is that DHT binds considerably more strongly to the androgen receptors inside hair follicles than testosterone does. On a scalp that is not genetically predisposed to pattern hair loss, that binding does not cause a noticeable problem. On a scalp that is genetically predisposed, it does, and that distinction, genetics rather than the DHT level alone, is central to understanding why pattern hair loss affects some people and not others even when hormone levels look similar on a lab panel.
How DHT affects genetically sensitive follicles
Hair follicles cycle through a growth phase, a short transition phase, and a resting phase before the cycle starts again. In people genetically susceptible to androgenetic alopecia, DHT shortens the growth phase of scalp follicles and shrinks them over time. In follicles that are genetically sensitive to DHT, repeated exposure gradually shortens that growth phase with each cycle. A follicle that once grew a thick hair for years at a stretch starts producing a finer, shorter hair sooner, then an even finer one after that. This stepwise shrinking is called miniaturization, and it is the process behind the gradual thinning most people associate with pattern hair loss, rather than a sudden, even hair loss across the whole scalp.
Miniaturization explains why pattern hair loss tends to follow a recognizable map on the scalp instead of appearing everywhere at once. Follicles at the hairline, temples and crown in men, and more diffusely across the top of the scalp in many women, are often more genetically sensitive to DHT than follicles at the back and sides of the head. That difference is also why hair moved from those less-sensitive areas during a transplant tends to keep growing normally once relocated. The pattern is driven by which follicles carry that genetic sensitivity, not by how much DHT is circulating in the body overall.
This is also why two people with comparable hormone levels can have very different experiences with hair thinning. The genetic sensitivity of the androgen receptors in scalp follicles, which is inherited and varies between individuals, matters at least as much as the raw amount of DHT being produced.
The role of the 5-alpha reductase enzyme
5-alpha reductase is the enzyme responsible for converting testosterone into DHT, and it exists in two main forms that matter for this topic. Type I is found mostly in the skin, sebaceous glands and liver. Type II is concentrated in hair follicles, the prostate gland and other reproductive tissue, and it drives the majority of DHT production that is relevant to scalp hair.
| Enzyme type | Where it is concentrated | Relevance to scalp hair |
|---|---|---|
| Type I | Skin, sebaceous glands, liver | Minor contributor to scalp DHT |
| Type II | Hair follicles, prostate, reproductive tissue | Main driver of scalp DHT production |
This division matters because it explains where treatments aimed at DHT focus their effect. A medication that inhibits type II 5-alpha reductase has a direct route to lowering the DHT that genetically sensitive scalp follicles are exposed to, without needing to change testosterone levels themselves.
How finasteride lowers DHT
Finasteride is FDA-approved for male pattern hair loss and works by inhibiting type II 5-alpha reductase, lowering DHT levels. With less DHT available to bind the androgen receptors in genetically sensitive follicles, the miniaturization process described above can slow, and for some people, follicles that were still capable of producing hair get the chance to do so again over time. Response varies by person, and finasteride does not change the genetic sensitivity of the follicles themselves, only the amount of DHT they are exposed to.
Finasteride has labeled side effects, including sexual side effects in a small share of users, which should be discussed with a clinician. Because finasteride lowers DHT throughout the body rather than only at the scalp, those side effects can include reduced libido or erectile difficulty. These effects are listed in the product labeling, and most resolve after stopping the medication, though anyone considering finasteride should discuss the full side effect profile with a clinician before starting, and report any side effects that occur. A clinician can also help weigh finasteride against dutasteride, a related medication that inhibits both types of 5-alpha reductase rather than type II alone.
Other options and who they suit
Not everyone is a candidate for a DHT-lowering medication, and not everyone wants to take one, which is why finasteride is only one option among several. Topical minoxidil works through a different mechanism and does not lower DHT. It is thought to push resting follicles into an active growth phase and may improve blood flow to the scalp instead. That makes minoxidil a reasonable option for people who want to avoid a DHT-based approach, who are not candidates for finasteride, or who want to combine two mechanisms rather than rely on one. Our guide to minoxidil side effects covers what to expect from that option in more detail.
Combining a DHT-lowering medication with a treatment that works through a separate mechanism, such as topical minoxidil, is a common approach because the two address different parts of the process rather than overlapping. Our guide to combination hair loss treatments goes through how clinicians typically think about pairing options.
DHT is also worth asking about for anyone already on testosterone therapy, since testosterone is the hormone DHT is made from, and some people notice changes in their hair pattern after starting treatment. Our guide to testosterone therapy and hair loss looks at that connection specifically. In every case, which option, or combination of options, makes sense depends on an individual's pattern of hair loss, medical history and preferences, which is why an evaluation by a licensed clinician is the starting point rather than a guess based on what worked for someone else.
The bottom line
DHT is a normal hormone made from testosterone by the enzyme 5-alpha reductase, and in people genetically susceptible to pattern hair loss, it gradually shortens the growth phase of sensitive scalp follicles and shrinks them over time. Type II 5-alpha reductase, concentrated in hair follicles, is the main driver of that process on the scalp, which is why finasteride, an FDA-approved medication that inhibits this enzyme, can change the course of hair thinning for some people by lowering the DHT those follicles are exposed to. Other options, including topical minoxidil, work through different mechanisms entirely and do not lower DHT. Results vary by person, and the right approach, or combination of approaches, is a decision to make with a licensed clinician rather than on your own. You can find more in our Better Hair section.
Important Safety Information
Indication. Finasteride (1 mg) is an FDA-approved, prescription-only oral medication for male pattern hair loss, taken daily. It works by inhibiting type II 5-alpha reductase to lower DHT levels.
Common side effects. Sexual side effects, including decreased libido, erectile difficulty and decreased semen volume, in a small share of users; breast tenderness or enlargement in rare cases.
Warnings. Finasteride is not for use by women who are or may become pregnant, due to a risk to a male fetus; pregnant women should avoid handling crushed or broken tablets. It can lower PSA levels used in prostate cancer screening, so tell your clinician you are taking it before any PSA test. Report any new or worsening side effects to your clinician.
Talk to your doctor. This information is educational and is not a substitute for medical advice. Only a licensed medical professional can determine whether a treatment is right for you. Talk to your doctor about the benefits and risks, and report any side effects.
Frequently asked questions
Does lowering DHT regrow hair that has already been lost completely?
Lowering DHT is generally thought to help follicles that are still miniaturized but have not stopped producing hair altogether, by slowing or partially reversing that process. A follicle that has stopped producing hair for a long period is less likely to respond, which is one reason clinicians often emphasize starting treatment earlier rather than later. Results vary by person, and no specific outcome can be promised in advance.
Is DHT harmful to the rest of the body?
No. DHT has normal, necessary roles outside the scalp, including effects on the prostate gland and on body and facial hair growth. It is not a harmful hormone in general; the issue specific to pattern hair loss is that genetically sensitive scalp follicles respond to DHT in a way that shortens their growth cycle over time, which does not reflect how DHT functions elsewhere in the body.
Why do some people respond to finasteride and others do not?
Response depends on factors including how far miniaturization has progressed in a given follicle and individual variation in how someone's hair follicles respond to a lower DHT level. Finasteride lowers DHT, but it does not change the underlying genetic sensitivity of the follicles themselves, which is part of why response is not the same for everyone.
Does minoxidil lower DHT the way finasteride does?
No. Topical minoxidil works through a different mechanism; it is thought to push resting follicles into an active growth phase and may affect blood flow to the scalp, and it does not lower DHT. That is one reason minoxidil and a DHT-lowering medication are sometimes used together, since they act on different parts of the process rather than the same one.
What are the main side effects to ask a clinician about with finasteride?
Finasteride's labeled side effects include sexual side effects, such as decreased libido or erectile difficulty, in a small share of users, along with breast tenderness or enlargement in rare cases. Most reported sexual side effects resolve after stopping the medication. A clinician can review the full side effect profile and any individual risk factors before you start.
Can women take finasteride for DHT-related hair loss?
Finasteride is FDA-approved specifically for male pattern hair loss, and it carries a specific warning against use by women who are or may become pregnant, due to a risk to a male fetus. Whether any DHT-related treatment is appropriate for a woman's hair loss pattern is a decision for a licensed clinician, since female pattern hair loss involves some different considerations.
