Baldness: definition and main types

What is baldness? Definition and main causes

Baldness is the progressive and structural loss of hair, driven by a combination of genetic and hormonal factors. The technical term is androgenetic alopecia. It affects approximately 80% of men and 50% of women by age 70. It is not a disease: it is a physiological condition that accelerates the hair follicle cycle. Hairs shorten the growth phase (anagen) and bring forward the resting phase (telogen), until they stop regrowing altogether.

The main culprit is dihydrotestosterone (DHT), a derivative of testosterone. DHT attaches to androgen receptors in the hair follicles of the scalp, progressively miniaturizing them. It all starts with a genetic predisposition: the androgen receptor gene is on the X chromosome, so baldness is often inherited from the mother. Nearly 95% of male hair loss cases follow this pattern.

It is not just a matter of DHT and genetics. Chronic stress, thyroid imbalances, iron or zinc deficiencies, and certain inflammatory scalp conditions can also intervene, accelerating the process. About 20% of women with androgenetic alopecia also have polycystic ovary syndrome, which alters the hormonal profile. In clinical practice, the hereditary component remains central: if your father or grandfather was bald, the probability rises above 60%.

Men and women do not lose hair in the same way. In men, hair loss almost always begins at the temples or the crown, leading to the classic receding hairline or thinning of the top. In women, it instead presents as diffuse thinning on the top of the scalp, with the frontal hairline generally preserved. The underlying causes are identical, but female hormonal receptors respond to DHT less aggressively, which is why women lose hair more slowly and rarely become completely bald.

Baldness does not arise from 'poor circulation' or 'excess sebum', no matter how often it is repeated. On social media and e-commerce sites, those selling miracle creams exploit precisely these myths.

Baldness and alopecia: fundamental differences

Baldness and alopecia are used as synonyms, but they are not. The difference is clear, and understanding it leads to the right treatments. Alopecia is the medical term for any hair loss, temporary or permanent, localized or diffuse. Baldness is instead a specific type: androgenetic alopecia, which manifests with a receding hairline and a patch on the crown. 70% of men over 70 have some degree of baldness. But not all hair loss leads there.

To frame what baldness is and types of alopecia, the starting point is the causes. Androgenetic alopecia, the so-called common baldness, depends on genetic and hormonal factors. DHT, in particular, reduces the lifespan of the follicle. Other forms of alopecia stem from different causes. Alopecia areata, for example, is an autoimmune disease: it affects about 2% of the population and manifests with round patches that often regrow on their own. Telogen effluvium is a diffuse but temporary shedding, triggered by stress, high fever, or childbirth. There are also scarring forms, much rarer, where the follicle is destroyed and does not regrow.

The confusion arises because many use 'alopecia' for any type of hair loss, and 'baldness' only for male pattern hair loss. In reality, a woman can suffer from baldness (female androgenetic alopecia) and a man can have temporary alopecia areata. In essence, baldness is always a form of alopecia, while not all alopecia is baldness. Knowing this avoids wasting money on the wrong products. A patient with telogen effluvium does not need minoxidil: they need to manage stress. Someone with hereditary baldness, on the other hand, must intervene early: medication or a transplant.

How many types of baldness exist? Complete classification

Baldness is not a single condition. There are different forms, each with specific causes, progression, and treatments. Distinguishing them is the first step to understanding what to do.

Androgenetic alopecia (AGA): the most common

It affects about 80% of men over 70, but it starts much earlier, often as early as 20-30 years old. The cause is genetic: the follicles are sensitive to dihydrotestosterone (DHT). In men, the pattern follows the Norwood scale, bilateral temple recession and thinning of the crown. For women, the Ludwig scale shows diffuse thinning on top of the head, without involving the temples. It does not happen overnight: it is measured in years, not weeks. A 45-year-old man with advanced temple recession can still have healthy hair on the nape and sides, areas that usually remain resistant to DHT.

Alopecia areata: patchy

It affects about 2% of the world population, without distinction of sex or age. It presents with round, smooth patches, without inflammation: hair falls out within 24-48 hours. The immune system targets follicles in the anagen phase. It has no predictable course: one patch may regrow on its own in six months, or it may progress to alopecia totalis (loss of all scalp hair) or universalis (loss over the entire body). In the clinic, I often see a patient with three two-centimeter patches that resolve on their own, while another with a single persistent patch does not improve even with corticosteroids.

Telogen effluvium: temporary

A reactive, non-pathological form. Two to three months after a triggering event, such as childbirth, high fever, surgery, intense stress, or a drastic diet, a higher than normal amount of hair is lost. This means 150-300 hairs per day, instead of the physiological 50-100. It is almost always reversible. Pull tests are positive across the entire scalp, whereas in alopecia areata they are positive only on the patches.

Comparison of the main types of baldness TypeTypical agePatternReversibility Male androgenetic alopecia20-60 yearsReceding hairline + crownSlowing possible, not reversible Female androgenetic alopecia30-60 yearsDiffuse thinning on the crownSlowing possible, not always reversible Alopecia areataAny ageRound patchesSpontaneous in 50% of cases within 12 months Telogen effluviumAny ageDiffuse, uniformAlmost always complete within 6-9 months Cicatricial alopecia (Lichen planus pilaris)30-60 yearsPatches with redness and scalingPermanent. Follicle destroyed

Male and female baldness: differences and genetics

Not all types of baldness present themselves. The differences between men and women are profound: the pattern of loss and the speed of progression are different, and the role of genetics varies. To understand what baldness is and its types, these distinctions must be clarified.

In men, androgenetic alopecia (AGA) follows a predictable pattern. It starts at the temples, what many call 'receding hairlines', and at the crown, then extends to involve the entire frontal area. The Norwood scale lists at least seven stages. In women, the loss is more diffuse: thinning affects the upper part of the scalp, while the frontal hairline often remains intact for years. For women, the Ludwig scale is used, which includes three grades. Statistically, about 50% of men over 50 show some degree of baldness. In women, the percentage is lower, but it increases sharply after menopause, reaching 30-40% around age 60.

The role of genes

In both sexes, the main cause remains the same: a genetic predisposition to the action of dihydrotestosterone (DHT) on the follicles. The most studied gene remains the androgen receptor (AR) gene, located on the X chromosome. It is not the only one. Variations in genes such as HDAC9, EDA2R, and WNT10A also influence the final phenotype. Male baldness is polygenic. It can come from both sides of the family, not just from the mother or father. In women, the genetic component is less straightforward. Heredity is multifactorial, and the overall hormonal balance matters a lot. A patient with polycystic ovary syndrome or early menopause is more likely to develop thinning, even without a strong family history.

Why recognizing the differences is useful

Treatments change. In men, minoxidil and finasteride have decades of studies behind them and work well on at-risk areas. In women, finasteride is not approved: it is used off-label only in selected cases, while therapy focuses on minoxidil and hormonal modulators like spironolactone. Even transplant surgery follows different logic: on a woman with diffuse thinning, the same result cannot always be achieved as on a man with a well-defined bald area.

What baldness is and its types is not a purely theoretical question. It is the foundation for choosing the right path, without wasting time on solutions that do not fit one's own pattern.

The 4 types of hair and their role in baldness

Each hair on the scalp follows a life cycle. The cycle consists of four phases, and baldness inserts itself right here, altering this mechanism. Knowing the types of hair helps to understand what baldness is and the types of loss that can be addressed.

Anagen, the active growth phase. The anagen phase lasts from two to six years. On a healthy scalp, almost 90% of hairs are in the anagen phase. When this phase shortens, the hair falls out earlier.