Male pattern baldness is driven by a hormone called dihydrotestosterone, or DHT, acting on hair follicles that are genetically programmed to be sensitive to it. That two-part explanation, hormones plus inherited vulnerability, has been the standard answer for decades. But research over the past fifteen years has revealed that the process is far messier than “too much DHT kills your hair.” Inflammation, prostaglandins, disrupted growth signals, reduced blood flow, and even your scalp’s bacterial community all appear to play roles in turning thick terminal hairs into the fine, barely visible strands that characterize a balding scalp.
DHT and the Enzyme That Makes It
Testosterone itself is not the main culprit. An enzyme called 5-alpha reductase converts testosterone into DHT inside the hair follicle, and it is DHT that does the damage. Bald scalp carries measurably higher concentrations of DHT than haired scalp on the same head. In one study of men with pattern baldness, average DHT levels in bald skin were about 7.4 pmol/g compared to roughly 4.2 pmol/g in areas still growing hair, even though testosterone levels were similar in both regions.1The Journal of Clinical Endocrinology & Metabolism. The effect of finasteride, a 5 alpha-reductase inhibitor, on scalp skin testosterone and dihydrotestosterone concentrations in patients with male pattern baldness The problem is not how much testosterone circulates in your blood; it is how efficiently your follicles convert it into DHT and how strongly they respond to it.
This is why men who are castrated before puberty never develop pattern baldness, and why drugs that block 5-alpha reductase can slow or partly reverse hair loss. Finasteride blocks the type 2 form of the enzyme, reducing DHT in the scalp.2PubMed Central. Finasteride-its impact on sexual function and prostate cancer Dutasteride blocks both types 1 and 2, lowering scalp DHT even further in a dose-dependent way.3PubMed. The importance of dual 5alpha-reductase inhibition in the treatment of male pattern hair loss: results of a randomized placebo-controlled study of dutasteride versus finasteride Both drugs demonstrate that reducing DHT at the follicle can halt or slow the process, which is strong evidence that DHT is central to it. But neither drug works for everyone, and regrowth is often modest, hinting that DHT is necessary but not sufficient.
What DHT Actually Does to a Follicle
The visible result of male pattern baldness is miniaturization. Terminal hairs, the thick pigmented strands that make up a full head of hair, progressively shrink into vellus-like hairs, the wispy colorless fuzz you can barely see. Histologically, this shows up as a shrinking dermal papilla, the cluster of cells at the base of the follicle that orchestrates each hair cycle. One hypothesis is that miniaturization reflects a direct reduction in the number of dermal papilla cells, which shrinks the papilla and in turn produces a thinner, shorter hair.4PubMed. Possible mechanisms of miniaturization during androgenetic alopecia or pattern hair loss This shrinkage can happen in a single hair cycle as an abrupt step rather than a gradual slide, which helps explain why hair loss sometimes seems to accelerate suddenly.
Alongside miniaturization, the growth phase of each hair cycle gets shorter. A healthy scalp hair can grow for two to six years before entering a resting phase and falling out. In balding follicles, that active growth phase progressively truncates, so hairs spend less time growing and more time resting or shedding.5PubMed. Frontiers in the physiology of male pattern androgenetic alopecia: beyond the androgen horizon The combination of thinner hairs and shorter growth cycles is what produces the visible thinning and eventual bareness.
How Genetics Determine Who Loses Hair
If DHT were the whole story, every man with normal testosterone would go bald. The reason some do and some don’t is overwhelmingly genetic. A large genome-wide analysis of UK Biobank participants estimated that roughly 94% of the variation in male pattern baldness liability could be attributed to genetic factors, with about 82% from autosomal chromosomes and 12% from the X chromosome.6Nature Communications. GWAS for male-pattern baldness identifies 71 susceptibility loci explaining 38% of the risk That X-chromosome contribution is why your mother’s father’s hair is often mentioned as a predictor, since you inherit your single X chromosome from your mother. But autosomal genes matter far more in total, which means your father’s side of the family counts too.
A separate analysis found that common genetic variants across autosomes explained about 47% of the variance in baldness, with X-chromosome variants adding another 5%.7PubMed Central. Genetic prediction of male pattern baldness The gap between these two numbers and the 94% total heritability figure reflects the fact that rarer variants and gene-gene interactions also play a role. Researchers have identified at least 71 independent genetic loci linked to baldness risk. These genes influence everything from androgen receptor sensitivity to follicle development pathways. No single gene makes or breaks the outcome; it is a cumulative genetic load, which is why baldness severity runs on a spectrum.
Growth Signals Gone Wrong
One of the more specific ways DHT damages follicles involves a growth-signaling pathway called Wnt. In a healthy follicle, Wnt signals tell stem cells in the hair bulge to wake up and start building a new hair. DHT appears to sabotage this process selectively in genetically susceptible follicles. When dermal papilla cells from balding scalps are exposed to DHT, they suppress Wnt-driven keratinocyte growth, something that does not happen in dermal papilla cells from non-balding men.8The Journal of Clinical Endocrinology & Metabolism. Keratinocyte Growth Inhibition through the Modification of Wnt Signaling by Androgen in Balding Dermal Papilla Cells The difference is not that balding follicles have DHT and non-balding ones don’t. The difference is in how their cells respond to it.
At the molecular level, DHT pushes these susceptible cells to dial down Wnt growth promoters and dial up Wnt inhibitors like DKK-1.9PubMed. Androgens modify Wnt agonists/antagonists expression balance in dermal papilla cells preventing hair follicle stem cell differentiation in androgenetic alopecia The result is that hair follicle stem cells are not getting the “grow” signal they need. Research also shows that androgen signaling causes a key protein involved in the Wnt pathway to be degraded more rapidly in balding dermal papilla cells.10PubMed. Hair follicle stem cell differentiation is inhibited through cross-talk between Wnt/β-catenin and androgen signalling in dermal papilla cells from patients with androgenetic alopecia So the stem cells are still there in a balding scalp; they just aren’t being told to do their job.
Prostaglandin D2 and the Inhibitory Signal
Beyond disrupted Wnt signaling, balding follicles produce elevated levels of a lipid molecule called prostaglandin D2, or PGD2. Researchers found that PGD2 and the enzyme that produces it are both significantly higher in bald scalp compared to haired scalp in men with pattern baldness. When PGD2 was applied to human hair follicles in the lab or to mice topically, it inhibited hair growth. The effect depended on a specific receptor called GPR44.11PubMed Central. Prostaglandin D2 inhibits hair growth and is elevated in bald scalp of men with androgenetic alopecia This finding was exciting enough to spark drug development targeting GPR44, though effective treatments based on it have not yet reached the market.
The prostaglandin story also connects to existing treatments. Minoxidil, the over-the-counter topical treatment, stimulates production of different prostaglandins and vascular endothelial growth factor while also promoting cell proliferation in follicle cells.12PubMed. Minoxidil: mechanisms of action on hair growth It may be partly counteracting the prostaglandin imbalance in balding skin, though its exact mechanism remains surprisingly uncertain after decades of clinical use.
Inflammation and Scarring Around the Follicle
Balding is not simply a matter of follicles shrinking in otherwise healthy tissue. Inflammation plays a significant, often underappreciated role. A histopathologic study found perifollicular inflammation and fibrosis in 81% of patients, particularly in those over 44, with advanced baldness, or with poor response to treatment. The inflammatory infiltrate was concentrated around the upper portion of the follicle and included specific immune cells.13PubMed Central. Perifollicular Inflammation and Fibrosis in Androgenetic Alopecia: Implications for Diagnosis and Treatment – A Comparative Histopathologic and Clinical Study with Normal-Appearing Scalp Over time, this inflammation leads to fibrosis, replacing the flexible tissue around the follicle with stiff scar-like collagen.
Research increasingly frames this as a vicious cycle. Androgen-driven changes provoke low-grade inflammation, which in turn triggers enzymes that degrade the collagen matrix surrounding follicles. Aging and glycation further stiffen this matrix, locking follicles into a miniaturized, low-output state.14PubMed Central. From a stem-cell-centered to a niche-centered view: the core role of collagen networks in hair loss and hair follicle miniaturization If fibrosis becomes severe enough, the follicle’s niche may be irreversibly damaged, which could help explain why long-standing baldness is harder to reverse than early-stage thinning.
Blood Flow and Oxygen Deprivation
Bald scalp has measurably less blood flow and lower oxygen levels than haired scalp on the same person. One study found a clear microvascular insufficiency and tissue hypoxia in balding regions that had not been reported before.15PubMed. Transcutaneous PO2 of the scalp in male pattern baldness: a new piece to the puzzle Whether reduced blood flow is a cause of hair loss, a consequence of fewer metabolically active follicles, or both, is still debated. But the finding is consistent with the observation that treatments which increase scalp blood flow can sometimes promote regrowth. An apparatus designed to relieve scalp tension and increase blood flow showed a 40% efficacy rate for hair regrowth in one trial, accompanied by measurable increases in cutaneous blood flow and skin temperature.16PubMed. A new apparatus for hair regrowth in male-pattern baldness
Scalp tension itself may matter. The galea aponeurotica, the tight fibrous sheet under the skin on top of the head, creates mechanical tension in exactly the regions where baldness typically occurs: the crown and the frontal hairline. The sides and back of the head, which sit below this structure, are almost never affected. Some researchers think this mechanical environment contributes to reduced blood flow and increased androgen activity, though this remains a minority view compared to the mainstream DHT-genetics framework.
The Scalp Microbiome
Your scalp hosts a complex community of bacteria and fungi, and this community appears to shift in men with pattern baldness. A comprehensive sequencing study found that the age-related microbial patterns normally seen on a healthy scalp were disrupted in men with baldness due to severe microbial imbalances. These imbalances were not limited to bald patches but extended across the entire scalp.17PubMed Central. Microbial dysbiosis and its diagnostic potential in androgenetic alopecia: insights from multi-kingdom sequencing and machine learning A separate study looking inside the hair follicle itself found that miniaturized hairs in balding regions harbored elevated levels of a common skin bacterium in the middle and lower follicle compartments, which correlated with increased immune-response gene activity.18PLoS ONE. Microbiome in the hair follicle of androgenetic alopecia patients This microbiome shift could be contributing to the perifollicular inflammation described above, though the evidence is still correlational rather than causal.
Oxidative Stress and Dermal Papilla Senescence
The dermal papilla cells that orchestrate each hair cycle are vulnerable to oxidative stress, the accumulation of reactive oxygen species that damages cellular machinery. Research shows that when dermal papilla cells are pushed into premature senescence by oxidative stress, they lose their ability to properly communicate with the surrounding epithelial cells, compromising the follicle’s capacity to regenerate hair.19PubMed. Stress-induced premature senescence of dermal papilla cells compromises hair follicle epithelial-mesenchymal interaction In baldness, the situation appears to be a double hit: excessive DHT accumulation and oxidative stress together drive dermal papilla cells toward senescence.20PubMed Central. Oxidative Stress and Hormone-Regulated Dermal Papilla Cell-Targeted Nanomodulators: Reverse Cellular Senescence for Androgenetic Alopecia Therapy
Smoking may worsen this. A systematic review found that smoking can contribute to hair loss through several pathways, including free radical damage to follicle cells, promotion of cellular senescence, vasoconstriction that reduces blood flow to the scalp, and hormonal effects.21PubMed Central. Role of Smoking in Androgenetic Alopecia: A Systematic Review If you’re already genetically predisposed, smoking could be accelerating several of the mechanisms that drive thinning.
Sleep, Circadian Rhythms, and Hair Loss
An emerging line of research connects circadian biology to baldness. Clock genes, the molecular timekeepers that regulate your body’s daily rhythms, also play a role in regulating the hair growth cycle.22PubMed Central. Clock genes, hair growth and aging A study of young adults found that men with severe baldness had lower expression of a specific clock gene and a shifted peak in their circadian rhythm compared to men with little or no hair loss. Evening chronotypes, people who naturally stay up late and wake late, showed higher rates of baldness.23PubMed. Association between sleep patterns, circadian rhythms, and hair loss in young adults The findings are preliminary, and the researchers described the results as suggestive rather than conclusive. But they raise the possibility that chronically disrupted sleep could be one more environmental factor nudging genetically susceptible follicles toward miniaturization.
Baldness and Heart Disease Risk
Several studies have linked male pattern baldness, particularly early-onset or severe vertex baldness, to a moderately elevated risk of coronary heart disease. A meta-analysis of cohort studies found that men with severe baldness had roughly a 32% higher risk of coronary heart disease compared to men without baldness, a figure that rose to about 44% when the analysis was restricted to younger men.24BMJ Open. Male pattern baldness and its association with coronary heart disease: a meta-analysis A separate study found that early-onset baldness was associated with about three times the odds of needing coronary revascularization before age 60, even after adjusting for traditional cardiovascular risk factors.25PubMed. Early onset of androgenetic alopecia associated with early severe coronary heart disease: a population-based, case-control study
This does not mean baldness causes heart disease. A study that used a genetic risk score for baldness found no association between genetic baldness risk and coronary events, suggesting the link may be driven by shared risk factors like insulin resistance, inflammation, and elevated body mass rather than a direct causal connection.26PubMed Central. Male-pattern baldness and incident coronary heart disease and risk factors in the Heinz Nixdorf Recall Study Still, if you’re losing hair early and have other cardiovascular risk factors, the association is worth being aware of as extra motivation to manage the things you can control.
Why Women Lose Hair Differently
Women can develop androgenetic alopecia too, but the pattern and mechanism differ. Instead of a receding hairline and bare crown, women typically experience diffuse thinning across the top of the scalp while keeping their frontal hairline largely intact. Part of the explanation may be an enzyme called aromatase, which converts androgens into estrogens. Research has found that women’s frontal follicles have aromatase levels roughly six times higher than men’s frontal follicles, potentially exerting a protective effect by converting DHT’s precursors into estrogen before they can do harm.27Anais Brasileiros de Dermatologia. Female Pattern Hair Loss: a clinical and pathophysiological review This enzyme difference helps explain why the frontal hairline is typically preserved in women and why female pattern hair loss responds differently to treatment than the male version.
Diagnosing and Measuring Progression
A dermatologist can usually diagnose male pattern baldness on sight, but trichoscopy, a specialized magnification technique for examining scalp and hair, reveals the process in more detail. The hallmark finding is hair diameter variability, meaning a mix of thick terminal hairs and thin miniaturized ones growing side by side. A systematic review of trichoscopy in androgenetic alopecia found this variability in over 94% of patients. Other common features included vellus hairs and a “peripilar sign,” a brownish halo around the hair shaft indicating inflammation.28PubMed Central. Trichoscopy of Androgenetic Alopecia: A Systematic Review These findings can help distinguish early pattern baldness from other types of hair loss and track whether treatment is working.
Platelet-Rich Plasma and Regenerative Approaches
Beyond the established treatments of finasteride and minoxidil, platelet-rich plasma (PRP) injections have gained popularity as a hair-loss therapy. PRP is prepared from your own blood and concentrated to contain high levels of growth factors. These growth factors promote dermal papilla cell proliferation, thicken existing hair shafts, and push resting follicles back into the active growth phase. PRP also appears to prolong dermal papilla cell survival by activating anti-apoptotic pathways and signaling that promotes stem cell differentiation.29PubMed Central. Efficacy of Platelet-Rich Plasma in Males With Androgenetic Alopecia Results in clinical studies have been variable, partly because there is no standardized preparation protocol, so the concentration of growth factors differs from clinic to clinic. PRP is typically used as an adjunct to DHT-blocking drugs or minoxidil rather than a standalone treatment.
An Evolutionary Puzzle
If baldness is so common and so strongly genetic, an obvious question is why evolution didn’t eliminate it. One theory frames male pattern baldness as a signal of social maturity. Facial hair and a full head of hair are associated with physical prime, while baldness corresponds to a later stage of maturation. Under this “multiple fitness model,” baldness may have functioned as a signal of a non-threatening form of social dominance associated with experience and reliability rather than physical aggression.30Elsevier (Ethology and Sociobiology). The evolutionary significance and social perception of male pattern baldness and facial hair Whether or not this evolutionary speculation holds up, the fact that baldness persists across cultures and at high frequencies strongly implies it was not strongly selected against, and may have conferred some subtle social advantage in ancestral environments.