Androgenetic alopecia is the most common form of hair loss, caused by a combination of genetics and hormones that gradually shrink hair follicles until they produce only fine, barely visible strands. It affects roughly 50% of men by their late 40s and becomes increasingly common in women after menopause. You might know it as male pattern baldness or female pattern hair loss, but it’s the same underlying process in both cases.
What Causes the Hair to Thin
The central player is dihydrotestosterone, or DHT, a potent form of testosterone. An enzyme in your scalp converts regular testosterone into DHT, and this conversion happens at much higher rates in people with androgenetic alopecia. The balding areas of the scalp also have more receptors that respond to DHT, creating a concentrated hormonal environment that’s hostile to healthy hair growth.
When DHT binds to receptors on a hair follicle, it shortens the growth phase of the hair cycle. Normally, a single strand of hair grows for two to six years before entering a resting phase and falling out. In androgenetic alopecia, that growth window gets progressively shorter with each cycle. The follicle itself physically shrinks, a process called miniaturization. Over time, thick terminal hairs are replaced by wispy, colorless vellus hairs that may not even break through the skin’s surface. The follicle doesn’t die immediately, which is why early treatment can sometimes reverse the process.
The Role of Genetics
Androgenetic alopecia runs in families, though the inheritance pattern is complex. A key gene sits on the X chromosome, which is why people often look to their mother’s side of the family for clues. A specific variation in the androgen receptor gene roughly triples the risk, particularly in white populations. But this isn’t the whole story. Multiple genes contribute, and having a family history on either side increases your likelihood. Some people carry the genetic susceptibility but never develop significant hair loss, while others with minimal family history do. Hormonal levels, age, and individual follicle sensitivity all interact with genetic predisposition.
How It Looks in Men vs. Women
Men and women lose hair in distinctly different patterns. In men, thinning typically starts at the temples and the crown of the head. The hairline recedes into an M-shape, and a bald spot develops on top. Over years, these two areas expand and merge, eventually leaving only a horseshoe-shaped ring of hair around the sides and back of the head. This progression is mapped on the Hamilton-Norwood scale, which ranges from Type I (minimal recession) to Type VII (only the horseshoe remains). About 16% of white men between 18 and 29 already show at least moderate loss.
Women rarely go fully bald. Instead, hair thins diffusely across the top of the scalp while the frontal hairline stays mostly intact. The easiest way to spot it is by parting the hair down the middle: the part gradually widens, and more scalp becomes visible in a pattern sometimes described as resembling a Christmas tree shape when viewed from above. The Ludwig scale grades this from mild thinning (Grade I) to near-complete loss on the crown (Grade III), though most women stay in the earlier stages. Some women also develop mild recession at the temples, but this tends to follow its own course separate from the midline thinning.
How It’s Diagnosed
A dermatologist can usually diagnose androgenetic alopecia by examining the pattern of hair loss alone. For less obvious cases, a handheld magnifying device called a dermatoscope reveals telltale signs: hairs of widely varying thickness growing from the same area, a brownish discoloration around follicle openings, and an increased number of fine vellus hairs replacing thicker ones. Hair diameter diversity, meaning a mix of thick and thin hairs in the same region, is considered the most reliable marker and appears in virtually all cases.
Blood tests aren’t typically needed for men with a classic pattern. For women, especially those with irregular periods or signs of excess androgen like acne or facial hair, bloodwork may help rule out other causes such as thyroid disorders or iron deficiency that can mimic or worsen the condition.
Treatment Options and What to Expect
No treatment cures androgenetic alopecia, but several can slow the loss and, in many cases, partially reverse it. The earlier you start, the more follicles are still capable of responding.
Topical Minoxidil
Minoxidil is an over-the-counter liquid or foam applied directly to the scalp, available in 2% and 5% concentrations. It works by increasing blood flow to follicles and extending the growth phase of the hair cycle. The earliest effects on hair growth begin around 6 to 8 weeks, with maximum results typically appearing by 12 to 16 weeks. You need to keep using it indefinitely; stopping causes the regained hair to fall out within a few months.
Finasteride
Finasteride is a prescription pill that blocks the enzyme responsible for converting testosterone to DHT, reducing scalp DHT levels significantly. In clinical trials, men taking finasteride had 107 more hairs in a one-inch circle of scalp compared to placebo after 12 months. That gap continued to widen, reaching a 277-hair difference at five years. Peak improvement occurs after about a year, with minimal additional gains after four years of use.
Sexual side effects are the main concern: decreased sex drive occurred in 1.8% of men taking the drug versus 1.3% on placebo, and erectile issues in 1.3% versus 0.7%. Overall, 3.8% of men reported at least one sexual side effect compared to 2.1% on placebo. For most men the side effects resolve after stopping the medication, though persistent effects have been reported in rare cases. Finasteride is not approved for use in women who are or may become pregnant due to the risk of birth defects.
Other Approaches
Dutasteride, a more potent DHT blocker, produced clinical improvement in roughly 80% of patients after six months in studies, though it’s used off-label for hair loss in many countries. Low-level laser therapy, delivered through caps or combs worn at home, has shown improvement as early as three months that can last up to two years. Platelet-rich plasma injections, where concentrated growth factors from your own blood are injected into the scalp, have demonstrated increased hair density peaking around three months, with continued improvement at six months and one year. Combining treatments, such as minoxidil with finasteride, tends to outperform either one alone.
Hair transplant surgery remains the most definitive option for advanced loss. It relocates hair follicles from the resistant sides and back of the scalp to thinning areas. Because these follicles are genetically resistant to DHT, they continue growing in their new location. Most people still use medical therapy alongside transplantation to protect the remaining native hair.
Why Timing Matters
Androgenetic alopecia is progressive. Each hair cycle that passes under the influence of DHT leaves the follicle slightly smaller than before. Once a follicle has fully miniaturized and stopped producing visible hair, it becomes much harder to revive. The practical takeaway is that the treatments available today are far more effective at maintaining existing hair than regrowing what’s already been lost. Starting treatment when you first notice thinning, rather than waiting until loss is advanced, gives you the best chance of holding onto the hair you have.