Males are much more likely to experience baldness and hair loss than females. This is mainly due to genetic and hormonal differences between the sexes. Baldness in males is often referred to as male-pattern baldness or androgenic alopecia. It is estimated that around 50% of men will experience some degree of hair loss by the time they reach 50 years old.[1] In contrast, hair loss affects only around 30% of women by the age of 50.[2] But why is there such a difference between male and female baldness patterns? Let’s take a closer look.
The role of genetics
Genetics play a major role in determining baldness for both men and women. However, the specific genes involved differ between the sexes.
Male-pattern baldness is strongly associated with genetics. It is passed down from parents to children through genes. The main genes involved are the androgen receptor gene on the X chromosome and the 5-alpha reductase genes.[3] This is why baldness often runs in families on the mother’s side. Men who have close male relatives with baldness are more likely to develop hair loss themselves.
In women, genetics also play a role, but the inheritance patterns are not as straightforward as in men. Female pattern hair loss tends to run in families but can also occur sporadically.[4] Research has identified some genetic variants associated with female hair loss, but there are likely multiple genes involved that have not yet been fully identified.[5]
Androgen receptor gene
The androgen receptor gene on the X chromosome codes for the androgen receptor protein which allows cells to respond to androgens like testosterone and dihydrotestosterone (DHT). Variants in this gene can increase susceptibility to hair follicles miniaturizing in response to DHT.[6] Since this gene is located on the X chromosome, men only need one copy of a high-risk variant to be affected, while women need two.
5-alpha reductase genes
The 5-alpha reductase genes provide instructions for making the 5-alpha reductase enzymes that convert testosterone into DHT. Higher levels of these enzymes lead to more DHT buildup around hair follicles. Variants in these genes can increase baldness risk by raising DHT levels.[7]
The role of hormones
While genetics set the stage, differences in male and female hormone levels also influence baldness patterns.
Testosterone
Testosterone levels are much higher in men compared to women. Testosterone is converted into DHT with the help of 5-alpha reductase enzymes. High testosterone and DHT levels make men more susceptible to hair follicles miniaturizing and slowing hair growth.[8]
Estrogen
Women have much higher levels of estrogen than men. Estrogen may help counteract the effects of androgens like testosterone and DHT on hair follicles. Estrogen encourages hair growth by prolonging the anagen (growth) phase of hair follicles.[9] This may partially protect women against hair loss.
| Hormone | Typical Level | Effect on Hair |
|---|---|---|
| Testosterone in men | 270-1070 ng/dL | Raises DHT, leads to miniaturization of hair follicles |
| Testosterone in women | 15-70 ng/dL | Minimal effects on hair |
| Estrogen in men | 10-40 pg/mL | Minimal effects on hair |
| Estrogen in women | 30-400 pg/mL | Encourages hair growth |
Hair follicle sensitivity
Hair follicle sensitivity also differs between men and women. Male hair follicles have a greater number of androgen receptors compared to female follicles.[10] This makes them more sensitive to fluctuating androgen levels. Male hair follicles miniaturize more easily in response to DHT while female hair follicles are relatively resistant. But when women have conditions like polycystic ovary syndrome that increase testosterone output, they can experience hair loss similar to male-pattern baldness.[11] This demonstrates that given high enough androgen levels, female hair follicles are also susceptible to miniaturization.
Differences in hair growth cycles
Men and women also differ in their hair growth cycles. Each hair follicle on the scalp undergoes a growth cycle consisting of three main phases:[12]
- Anagen (growth) phase – can last 2-7 years
- Catagen (transitional) phase – lasts 2-3 weeks
- Telogen (resting) phase – lasts 2-3 months
At the end of the resting phase, the hair falls out and a new hair starts growing in the follicle beginning the cycle again.
On average, women have longer anagen (growth) phases than men, often lasting 5-7 years instead of 2-3 years.[13] This means female hair stays in the growth phase for longer periods before shedding. Longer anagen phases translate to longer hair length in women. Men have shorter growth cycles so hair is shed more frequently.
Hair cycling differences
| Phase | Women | Men |
|---|---|---|
| Anagen (growth) | 5-7 years | 2-3 years |
| Catagen (transitional) | 2-3 weeks | 2-3 weeks |
| Telogen (resting) | 2-3 months | 2-3 months |
With age, the anagen phase shortens for both men and women leading to shorter hair. But women maintain a hair growth advantage even in old age.[14] The relatively short growth cycles in men combined with genetic and hormonal factors cause bald areas to expand over time.
Receding hairlines versus diffuse thinning
There are also differences in the pattern and type of hair loss seen in men versus women:
- Men typically develop receding hairlines or bald patches concentrated on the top of the scalp and upper temples.
- Women experience diffuse thinning across the top of the scalp while the hairline is preserved.
The receding hairline seen in male-pattern baldness is related to hair follicles in the frontal and temple regions being especially sensitive to DHT levels. The dermal papilla cells on the temples and frontal scalp convert more testosterone into DHT through an enzyme called 5-alpha reductase type II which is present at higher levels in these areas.[15]
In contrast, women exhibit general hair thinning across the top of the scalp. Research suggests DHT levels do not vary much across the scalp in women. Rather, female hair loss is linked to an overall reduction in the density of hair follicles across the scalp compared to men who tend to show preservation of hair density outside balding zones.[16]
The stages of male pattern baldness
Male pattern baldness tends to progress in a predictable pattern characterized by the gradual miniaturization of hair follicles. This leads to hair loss following an typical pathway over time. The Norwood scale is the most common classification system used to describe the stages of male baldness:[17]
Norwood stage I – Minor recession of hairline at the temples and forehead.
Norwood stage II – Hair recession becomes more pronounced at temples forming an “M” shape.
Norwood stage III – Hair thinning continues at temples and vertex starts to thin.
Norwood stage III Vertex – Thinning concentrated at vertex while hairline recession is mild.
Norwood stage IV – Hairline recedes further and thinning increases at vertex joining together.
Norwood stage V – Bridge of hair separating temple recession and vertex bald spot is lost.
Norwood stage VI – Hair remains only on the sides and back of the scalp.
Norwood stage VII – Very little remaining hair.
Most men with male pattern baldness progress from stage I to stage V over 10-25 years, some faster and some slower. Aggressive balding can even progress to stage VII. Treatments work best when started in the early stages before too much hair has miniaturized.
Conclusion
In summary, male pattern baldness is much more prevalent than female hair loss due to a combination of genetic, hormonal, and environmental factors:
- Genetics – Male baldness has clearer inheritance patterns compared to complex female genetic factors.
- Hormones – High testosterone and DHT levels in men contribute to hair miniaturization.
- Hair follicles – Male follicles are more sensitive to DHT and have shorter growth cycles.
- Pattern – Men typically exhibit receding temples and vertex balding versus diffuse thinning in women.
Understanding these differences provides insights into why treatments for hair loss tend to work better for men versus women. Research continues into new therapies targeting the varied mechanisms of female hair loss. Early intervention remains key to maintaining both men’s and women’s hair.