5-alpha-reductase and hair loss: what it is and why it matters for DHT

The enzyme behind testosterone-to-DHT conversion in alopecia androgenetica

5-alpha-reductase is a key enzyme in the androgen pathway, responsible for converting testosterone into dihydrotestosterone (DHT). This biochemical step is clinically relevant because DHT plays a central role in androgen-sensitive hair loss patterns such as alopecia androgenetica.

Understanding how 5-alpha-reductase functions within the hair follicle environment helps clarify why the DHT pathway is frequently discussed in pattern hair thinning.

For a complete medical overview of androgen-driven hair loss, see our guide on alopecia androgenetica.

Read our guide on alopecia androgenetica
Schematische weergave van de omzetting van testosteron naar DHT via het enzym 5-alpha-reductase.

What Is 5-Alpha-Reductase?

5-alpha-reductase is a group of enzymes that catalyze the conversion of testosterone into DHT. DHT is a more potent androgen than testosterone and can have stronger biological effects in tissues that are androgen-sensitive.

DHT binds to androgen receptors within genetically susceptible hair follicles, contributing to structural changes over time.

In the context of hair, this matters because some scalp hair follicles are genetically predisposed to be sensitive to DHT.

How 5-alpha-reductase converts testosterone into DHT

The pathway can be summarized as:

  • Testosterone (circulating androgen)
  • 5-alpha-reductase (conversion enzyme)
  • Dihydrotestosterone (DHT)

DHT can then interact with androgen receptors in susceptible hair follicles.

For a deeper explanation of the hormone itself, see:

→ What is DHT and how does it affect hair?

Why DHT matters for hair follicles

In genetically predisposed individuals, DHT is associated with a progressive pattern of follicle changes often described as miniaturization:

  • The anagen (growth) phase becomes shorter
  • The follicle produces a thinner hair shaft
  • Hair density can decline over time

Miniaturization refers to the gradual reduction in follicle size, resulting in thinner and shorter hair fibers over successive growth cycles.

This mechanism is characteristic of alopecia androgenetica.

Types of 5-Alpha-Reductase

Research describes at least two primary isoenzymes (Type I and Type II), which differ in tissue distribution and activity levels.

In simplified terms:

  • Different isoenzymes may be more active in specific organs and tissue types
  • The scalp and hair follicle environment can be androgen-responsive
  • This is part of why DHT-related mechanisms are relevant in some hair loss patterns

This page is intended as an educational overview, not a diagnostic tool.

Approaches that target the 5-alpha-reductase pathway

Because 5-alpha-reductase is involved in DHT production, some medical and research strategies focus on influencing this enzymatic step.

Prescription options (medical context)

Certain medications are designed to inhibit 5-alpha-reductase activity and reduce DHT formation. These are regulated medical treatments and require professional evaluation.

Botanical and nutritional research

Some botanical extracts are investigated for their interaction with androgen pathways, including 5-alpha-reductase.

One example frequently discussed in the context of DHT-related hair thinning is saw palmetto.
→ Saw palmetto and DHT pathways

Important: botanical extracts do not function identically to pharmaceutical inhibitors.

Who might this be relevant for?

This pathway is mainly discussed in the context of androgen-sensitive patterns such as:

  • Male pattern hair loss (temples / crown thinning)
  • Female pattern thinning (widening part / crown density loss)

However, hair loss can also result from non-androgen mechanisms (for example telogen effluvium or inflammatory conditions). Identifying the underlying hair loss pattern is essential before focusing on DHT-related explanations.

This mechanism is primarily associated with alopecia androgenetica and is not typically the primary driver in stress-related or inflammatory hair loss conditions.

Summary

5-alpha-reductase is the enzyme responsible for converting testosterone into dihydrotestosterone (DHT). Because DHT influences genetically susceptible hair follicles, this enzymatic pathway is central to understanding androgenetic alopecia.

Recognizing whether hair thinning follows an androgen-sensitive pattern is essential before focusing on DHT-related mechanisms or interventions.

If your thinning pattern suggests androgen involvement, start with the medical overview and mechanism pages:

Frequently asked questions about 5-alpha-reductase and hair loss

What does 5-alpha-reductase do?

5-alpha-reductase is an enzyme that converts testosterone into dihydrotestosterone (DHT). This conversion increases androgen potency in tissues that are sensitive to DHT, including certain scalp hair follicles.

Does inhibiting 5-alpha-reductase reduce DHT levels?

Medical inhibitors of 5-alpha-reductase are designed to reduce DHT formation. Botanical extracts are studied for their potential interaction with this pathway, but they do not function identically to prescription medications.

Is 5-alpha-reductase involved in female hair thinning?

Androgen-sensitive hair thinning can also occur in women. While hormonal dynamics differ between sexes, DHT-related follicular sensitivity may still play a role in some female pattern hair loss cases.