The Best Hair Transplant Surgeons in the World: 2026 AHLA Guide
INTRODUCTION Medically reviewed by Aron G. Nusbaum, M.D., FAAD – April 28, 2026 There
Causes of Hair Loss
Androgenetic alopecia, commonly known as male pattern baldness, is responsible for more than 95% of hair loss in men. It can begin any time after puberty in men whose scalp follicles are genetically susceptible to androgen signaling, particularly the effects of dihydrotestosterone, or DHT.
Male pattern baldness is not simply caused by having high testosterone, and it is not inherited only from the mother’s side of the family. The condition is genetically complex and influenced by many genes inherited from both sides.
Men can also lose hair for reasons unrelated to androgenetic alopecia, including illness, medications, immune disorders, inflammation, infection, nutritional problems and disturbances of the normal hair growth cycle.
Why Male Pattern Baldness Develops
Male pattern baldness develops through the interaction of genetic susceptibility and androgen signaling within specific scalp follicles.
There is no single baldness gene. The androgen receptor gene on the X chromosome is important, but it represents only one part of a much larger genetic picture. Modern research has identified more than 380 genomic regions associated with androgenetic alopecia, involving androgen signaling, WNT signaling, follicle development and other biological pathways.
This is why the familiar idea that baldness comes only from a man’s maternal grandfather is incorrect. Genetic susceptibility can be inherited from both sides of the family, and men within the same family can experience very different ages of onset, patterns and degrees of hair loss.
Genetics establish susceptibility. Androgen signaling helps drive the progressive changes that occur within susceptible follicles.
A Closer Look at DHT
Dihydrotestosterone, commonly abbreviated DHT, is a potent androgen produced when the enzyme 5 alpha reductase converts testosterone into DHT.
DHT plays a central role in male androgenetic alopecia, but the important issue is not simply how much testosterone or DHT is circulating in the bloodstream. The critical factor is how genetically susceptible scalp follicles respond to androgen signaling.
Within susceptible follicles, DHT binds to androgen receptors and alters biological signals that regulate hair growth. Over repeated hair cycles, the active growth phase becomes shorter and the follicle gradually becomes smaller.
This process is known as follicular miniaturization.
A healthy terminal scalp follicle produces a relatively thick, long and pigmented hair. As miniaturization progresses, successive hairs become shorter and finer and provide progressively less scalp coverage. The follicle does not simply disappear overnight. For much of the process it remains present but produces increasingly miniaturized hairs.
This is one reason recognizing and treating androgenetic alopecia before extensive miniaturization has occurred can be important.
Male pattern baldness also does not mean that a man necessarily has abnormally high testosterone. Men with normal circulating androgen levels can develop extensive hair loss if their follicles are genetically susceptible, while other men can retain substantial scalp hair despite similar hormone levels.
Different follicles can even respond differently to the same androgen signal. Androgens can stimulate beard and body hair while contributing to miniaturization of susceptible follicles on the frontal scalp, mid scalp and crown.
Testosterone replacement therapy and anabolic androgen use can increase androgen exposure. In genetically susceptible men, this may accelerate or make androgenetic alopecia more apparent. Individual responses vary, and androgen therapy does not cause hair loss in every man who uses it.
Research is also examining inflammatory and fibrotic changes around miniaturizing follicles. These processes may contribute to progression and incomplete recovery in some patients, although genetic susceptibility and androgen signaling remain central to the established biology of male pattern baldness.
Male pattern baldness is not caused by wearing a hat, frequent shampooing, cutting the hair or poor scalp circulation. Everyday stress does not create the genetic process responsible for androgenetic alopecia. Significant physical or emotional stress can trigger telogen effluvium and may expose previously subtle pattern hair loss, but that is a different biological process. Repeated tension from tight hairstyles can cause traction alopecia, which is also a separate condition.
Additional Causes of Hair Loss
Androgenetic Alopecia
Androgenetic alopecia, or male pattern baldness, is a chronic, progressive and nonscarring form of hair loss in which genetically susceptible scalp follicles gradually miniaturize in response to androgen signaling. It most commonly affects the frontal hairline, temples, mid scalp and crown and can begin any time after puberty.
Effluviums
Effluviums are hair cycle disorders that produce excessive shedding or rapid hair loss. Telogen effluvium can follow illness, high fever, surgery, rapid weight loss, medications, hormonal changes or other physiological stress. Anagen effluvium disrupts actively growing hairs and is most commonly associated with chemotherapy, radiation and other severe insults to the growing follicle.
Alopecia Areata
Alopecia areata is an immune mediated form of nonscarring hair loss. It often produces smooth, well defined patches but can also cause diffuse or extensive loss involving the scalp, beard, eyebrows, eyelashes or other body hair. The follicles generally remain capable of regrowth.
Scarring Alopecia (Cicatricial Alopecia)
Scarring alopecia, also known as cicatricial alopecia, includes inflammatory disorders that can permanently destroy hair follicles and replace them with scar tissue. Warning signs can include pain, burning, itching, redness, scaling, pustules or loss of normal follicular openings. Some cases have few symptoms despite ongoing follicular damage. Early diagnosis is especially important because completely destroyed follicles generally cannot produce hair again.
Congenital Hypotrichosis
Hypotrichosis is a term dermatologists use to describe a condition of no hair growth. Unlike alopecia, which describes hair loss where there was formerly hair growth, hypotrichosis describes a situation where there wasn't any...
Hair Shaft Defects
Hair shaft disorders affect the structure, shape or strength of the hair fiber itself. Hair may break, remain unusually short or appear thin even when the underlying follicle is still capable of producing hair. Some shaft defects are inherited, while others result from heat, chemicals, friction, overprocessing or other forms of acquired damage. Breakage should therefore not automatically be mistaken for hair shedding from the follicle.
Infectious Agents
Fungal and bacterial infections of the scalp can cause inflammation, scaling, broken hairs, shedding and patchy hair loss. Some severe or prolonged infections can permanently damage follicles. Tinea capitis is an especially important cause of patchy hair loss in children, although scalp infections can occur at any age.
Treatment
Effective treatment begins with identifying the cause of the hair loss. For male androgenetic alopecia, oral finasteride and topical minoxidil are the FDA approved drug treatments in the United States, while other medical and surgical options may be appropriate for selected patients.
Treatments for other forms of hair loss can be completely different. An accurate diagnosis should therefore come before choosing a product, medication or procedure.
Featured Articles
Hair Loss Research, Treatment Advances, Hair Transplant Surgery and Consumer Protection
Long-Term Hair Loss Planning: Thinking Beyond Your First Hair Transplant
Medically reviewed by Aron G. Nusbaum, M.D., FAAD – April 28, 2026 Introduction Hair
The Real Risks of Hair Transplant Surgery: What Patients Need to Know
Medically reviewed by Aron G. Nusbaum, M.D., FAAD – April 28, 2026 Introduction Hair