Hair loss

Androgenetic alopecia follows a characteristic pattern. In men it typically affects the temples, the crown (vertex) and the middle of the front of the scalp [1]. In women it more often causes diffuse thinning over the top of the scalp with the frontal hairline preserved [3]. The condition is progressive and does not resolve on its own.

Telogen effluvium is diffuse shedding that begins weeks to months after a trigger such as a severe illness, surgery, childbirth, rapid weight loss, iron deficiency, thyroid disease or a new medication. It results from many follicles entering their resting phase at the same time, and hair usually regrows once the trigger is removed [2]. Alopecia areata causes round patches of hair loss when the immune system attacks hair follicles [3]. Other causes include hairstyles that pull on the hair, fungal scalp infections and cancer treatment [9].

The hair of the scalp grows in cycles, with a long growing phase (anagen) followed by a short resting phase (telogen) after which the hair is shed. In androgenetic alopecia, the growing phase shortens with each cycle while the resting phase stays the same or lengthens. The follicles also miniaturise, producing progressively finer and shorter hairs, until the hair no longer reaches the surface of the skin. Once the small muscle attached to each follicle has detached, the loss is likely to be irreversible [1].

The process depends on androgens (male sex hormones). Testosterone is converted to DHT by the enzyme 5-alpha reductase, and DHT acting on the scalp follicles drives the miniaturisation [8]. Normal androgen levels are enough to cause hair loss in people with a genetic susceptibility, so the condition reflects the sensitivity of the follicles rather than high hormone levels [1]. Prevalence varies by ethnic group; in white men, pattern hair loss affects at least half by age 50 [4].

A 2013 meta-analysis identified three cohort studies and three case-control studies of baldness and coronary heart disease, with 36,990 participants in total. In the cohort studies, men with severe baldness had a 32% higher risk of coronary heart disease than men without baldness (relative risk, the risk in one group relative to another, 1.32; 95% confidence interval 1.08 to 1.63). The association was of similar size in younger men, under 55 or 60 depending on the study (1.44). In the three studies that graded baldness pattern with the modified Hamilton scale, the risk rose with the severity of vertex baldness, while frontal baldness was not significantly associated [6].

The authors suggested that vertex baldness may be more closely related to atherosclerosis (the build-up of fatty plaque in the arteries) than frontal baldness, and called for further investigation [6]. Pattern hair loss is also increasingly identified as a risk factor for arterial stiffness [1]. Heart disease is covered under cardiovascular disease.

A 2022 meta-analysis of 19 studies with 2,531 participants compared people with androgenetic alopecia with controls. The pooled odds ratio (a measure of how much more common a condition is in one group) for metabolic syndrome was 3.46 (95% confidence interval 2.38 to 5.05). People with pattern hair loss also had higher body mass index, waist circumference, fasting glucose, blood lipids and blood pressure. Female sex, early onset of hair loss and African ethnicity were associated with a greater risk of metabolic syndrome [7]. Metabolic syndrome is a cluster of abdominal obesity, high blood pressure, high blood sugar and abnormal blood fats, described under metabolic health and type 2 diabetes.

The studies in the meta-analysis compared people at a single point in time, so they show that the conditions occur together but not which comes first [7].

Hair protects the scalp against sunburn and ultraviolet light, so the loss of hair exposes previously shielded skin [4]. Melanoma on the scalp and neck has a worse outlook than melanoma elsewhere. In 51,704 non-Hispanic white adults with a first invasive melanoma in US cancer registries from 1992 to 2003, five- and ten-year survival from scalp or neck melanoma was 83.1% and 76.2%, compared with 92.1% and 88.7% for melanoma at other sites. After adjustment for age, tumour thickness, sex and ulceration, patients with scalp or neck melanoma died of melanoma at 1.84 times the rate of patients with melanoma on the arms or legs (95% confidence interval 1.62 to 2.10). The authors urged clinicians to examine the scalp and neck carefully during skin examinations [5]. Sun damage to the skin is described under skin aging.

Two medicines are approved in the United States for male pattern hair loss: oral finasteride and topical minoxidil [1]. Finasteride blocks the type II 5-alpha reductase enzyme; a daily dose of 1 mg lowers DHT by 64% in the scalp and 68% in the blood [1]. In two 1-year randomised trials (studies that assign participants to groups by chance) of 1,553 men aged 18 to 41, with 1,215 continuing for a second year, finasteride increased the hair count in a 1-inch (5.1 cm²) circle of the balding crown, which started at an average of 876 hairs, by 107 hairs at one year and 138 hairs at two years compared with placebo. Men taking placebo continued to lose hair [8]. Sexual side effects such as erectile dysfunction and low libido are uncommon and most often resolve without stopping treatment; persistent effects have been reported, but their true frequency is unknown [1].

Minoxidil is applied to the scalp. In a 48-week trial of 393 men aged 18 to 49, 5% minoxidil solution was superior to 2% solution and to placebo in hair counts and in patient and investigator ratings, producing 45% more regrowth than the 2% solution, with more itching and local irritation [10]. Both medicines prevent further loss better than they reverse existing baldness, and both require continuous use to maintain the effect [1]. Hair transplantation moves follicles from the back of the scalp to balding areas [1].

Hair loss can affect self-image and is a cause of anxiety and depression in some men [1], and it can influence how others perceive the person affected [4].

Full deep dive: hair loss and health.

The link between baldness and heart disease comes from six observational studies, three of them case-control studies, and was not confirmed for frontal baldness [6]. Baldness is a marker, not a cause: there is no evidence that treating hair loss changes cardiovascular risk. The metabolic syndrome evidence comes from small studies that measured both conditions at one time, and its authors called for larger and more rigorously designed studies [7]. The scalp melanoma study was limited to non-Hispanic white adults and could not separate the effects of sun exposure, delayed detection and tumour biology [5]. The treatment trials studied men with pattern hair loss and lasted two years or less [8, 10].