The short answer: male pattern baldness happens when hair follicles that are genetically sensitive to a hormone called DHT gradually shrink over time. It is the most common cause of hair loss in men, driven by your genes and your hormones together rather than by anything you did wrong. The NHS notes that around half of men have some degree of hair loss by the age of 50, so if it is happening to you, you are in very ordinary company.
The medical name and what it means
Doctors call male pattern baldness androgenetic alopecia. The word breaks down usefully: 'andro' for androgens (male hormones), 'genetic' for the inherited element, and 'alopecia' meaning hair loss. In other words, it is hair loss driven by hormones acting on genetically susceptible follicles. We look at the hormone side in our DHT explainer.
Genes and DHT: the real cause of male pattern baldness
Two things combine. First, you inherit follicles with a certain sensitivity to dihydrotestosterone (DHT), a hormone made from testosterone by an enzyme called 5-alpha-reductase. Second, DHT acts on those sensitive follicles over years, shrinking them in a process called miniaturisation: each growth cycle produces a slightly finer, shorter hair, and the growing phase gets a little shorter each time, until the follicle produces little or no visible hair. Importantly, the follicle is not destroyed early on, which is why treatment started in good time can still make a difference.
This is why hair loss is patterned rather than uniform. The follicles at the temples and crown tend to be the most DHT-sensitive, while those around the back and sides are usually resistant, which is why hair often persists there even in advanced loss. That resistance is also what makes the back and sides useful as a donor area if a transplant is ever considered.
The pattern male pattern hair loss follows
Male pattern loss typically starts with the hairline receding at the temples, forming an M shape, and thinning at the crown. Over time these areas can meet. Clinicians often describe the stage using the Norwood scale, which we cover in the Norwood scale explained.
The pace is usually slow and uneven. Many men go through a phase where the hair is thinner but still present, before the change becomes obvious in a mirror. Because the process is gradual, people often underestimate how much has changed, which is one reason standardised photos over time are more reliable than memory.
Why it happens with age
Pattern loss is partly a function of cumulative exposure: the longer sensitive follicles are exposed to DHT, the more miniaturisation accrues. That is why the same genetic tendency shows up as a receding hairline in one man's twenties and only thinning at the crown in another man's fifties. Age is not the cause, but time under hormonal pressure is part of the picture, and it is why loss that starts early tends to reach a more advanced stage over a lifetime.
At what age does male pattern baldness start?
Male pattern baldness can begin any time after puberty. Some men notice a receding hairline or thinning crown in their late teens or twenties, while others see little change until their forties or fifties. Because early onset tends to signal a greater lifetime extent of loss, treatments such as finasteride are usually more effective the sooner they start. The rate is highly individual and largely set by your genes, so there is no single age at which it is due to appear.
The mother's father myth
A stubborn myth says baldness comes only from your mother's father. There is a grain of truth, because one important gene sits on the X chromosome, which men inherit from their mother. But the reality is that many genes are involved, and they come from both sides of your family. Looking at your father, his brothers and both grandfathers gives a fuller picture than any single relative, though even a strong family history is a guide rather than a guarantee.
What does not cause male pattern baldness
Wearing hats, frequent washing, styling products and blocked pores do not cause pattern baldness. Nor does 'clogged' sebum. These myths are persistent but not supported by evidence, and we address them in our hair loss myths article. Genuine causes of loss other than the androgenetic pattern, such as stress-related shedding or thyroid problems, follow different patterns and are worth distinguishing, because they call for different action.
What causes female pattern hair loss?
Women can experience a related condition called female pattern hair loss, also a form of androgenetic alopecia. It usually shows as diffuse thinning across the top of the scalp, widening at the parting, rather than the receding hairline seen in men, and the hormonal picture is less clear-cut. Treatment differs too: topical minoxidil for women is the mainstay, and a clinician will often check for contributors such as iron deficiency or thyroid problems before settling on a plan.
Can male pattern baldness be stopped?
You cannot change your genes, but you can influence the hormonal pressure on your follicles. Treatments that lower DHT or support the growth phase can slow the process and, in some men, thicken hair that has thinned but not yet disappeared. There is no cure that regrows hair lost long ago, so it is worth being realistic about what any option can deliver. The British Association of Dermatologists sets out the recognised options, and a clinician can assess your pattern and talk through whether treatment is worthwhile for you. The single biggest lever you have is timing: acting while you still have hair to protect.
