Hair loss, also known as alopecia, refers to the loss of hair on the body. There are various types of hair loss, all of which tend to differ in their underlying causes, prevalence, and the pattern in which hair is lost. Common types of hair loss include male- and female-pattern hair loss (collectively referred to as androgenic alopecia; AGA), alopecia areata, telogen effluvium, and anagen effluvium.^[35]

Male-pattern hair loss typically begins with hair loss at the front of the hairline and/or on the crown of the head, with hair loss progression over time.^[36] Female-pattern hair loss tends to feature diffuse hair thinning and hair loss across the top of the head, especially near the center of the scalp.^[36] Alopecia areata involves hair loss in patches, which can regrow or precede complete loss of hair. Telogen effluvium and anagen effluvium both involve hair thinning and hair loss across the scalp.

A medical professional may use various methodologies to diagnose hair loss, including visual examination, medical history, biopsy, and laboratory testing.^[37]

One test often employed is a hair pull test.^[38] During this procedure, a small section of hair is grasped and gently pulled on, with the process repeated at various areas of the scalp. The number of hairs that come out upon pulling can indicate if hair loss is occurring and its severity. Additionally, examination of the hairs that fall out can help establish what type of hair loss is occurring.

The only two drugs currently approved by the FDA for the treatment of androgenic alopecia are minoxidil (used topically) and finasteride (taken orally).^[35] Of these, minoxidil is approved for the treatment of both male- and female-pattern hair loss, while finasteride is only approved for men with male-pattern hair loss. Other treatments used for androgenic alopecia include dutasteride, prostaglandin analogs (e.g., latanoprost), injection with platelet-rich plasma, and anti-androgens (for women with hair loss due to high androgen levels).

The first-line treatment for alopecia areata is the injection of corticosteroids into sites of hair loss.^[39]

Several RCTs have tested the effect of individual supplements on hair loss, given either orally (including vitamin E and saw palmetto) or applied topically to the scalp (including pumpkin seed oil, melatonin, and procyanidin from apples).^[40] A number of studies have also examined the effect of oral supplements containing a mixture of compounds, typically a combination of nutrients (e.g., amino acids and vitamins).

Research on the effect of diet on hair loss is very limited. One small case-control study found that men with high intakes of either raw vegetables or fresh herbs were less likely to have AGA.^[41] In rare cases, certain nutrient deficiencies may lead to hair loss (especially in susceptible individuals), with one example being iron-deficiency anemia.^[42]

Low-level laser therapy (LLLT) involves the application of red and infrared light onto areas of the scalp, and available evidence indicates LLLT can prevent hair loss and potentially support hair regrowth in AGA.^[43]

Microneedling (a procedure in which the skin is repeatedly punctured by a large number of very small needles) may be able to enhance the effects of minoxidil in preventing hair loss and producing hair regrowth in AGA.^[44]

Ketoconazole is an antifungal medication that may reduce hair loss and potentially promote hair regrowth in AGA when applied to the scalp via medicated shampoo.^[45]

Male-pattern baldness is due in large part to an androgen (a so-called “male hormone") called dihydrotestosterone (DHT), which can sometimes contribute to female-pattern baldness as well. Other factors – like aging and genetics – can also increase the risk of male- and female-pattern baldness.

Alopecia areata is the result of the body's immune cells attacking hair follicles, resulting in inflammation and eventual hair loss.

Hair loss can also be the result of medical conditions, medications, and infection.