[4] The condition is caused by a combination of male sex hormones (balding never occurs in castrated men) and genetic factors.

[5] Some research has found evidence for the role of oxidative stress in hair loss,[6] the microbiome of the scalp,[7][8] genetics, and circulating androgens; particularly dihydrotestosterone (DHT).

[3] Men with early onset androgenic alopecia (before the age of 35) have been deemed the male phenotypic equivalent for polycystic ovary syndrome (PCOS).

[9][10][11][12] The cause in female pattern hair loss remains unclear;[3] androgenetic alopecia for women is associated with an increased risk of polycystic ovary syndrome (PCOS).

[22] With younger males, studies found metabolic syndrome to be at approximately a 4× increased frequency, which is deemed clinically significant.

It appears to be the result of genetic changes that make the activity of hair follicles on the scalp become sensitive to the presence of androgenic hormones, cholesterol, and proteins such as insulin-like growth factor.

[30] Male-pattern hair loss appears to be undergoing positive sexual selection in European and Asian populations.

With increasing age, androgens stimulate hair growth on the face, but can suppress it at the temples and scalp vertex, a condition that has been referred to as the 'androgen paradox'.

At the level of the somatic stem cell, androgens promote differentiation of facial hair dermal papillae, but inhibit it at the scalp.

[49] Premature androgenic alopecia and insulin resistance may be a clinical constellation that represents the male homologue, or phenotype, of polycystic ovary syndrome.

[52] In support of the association, finasteride improves glucose metabolism and decreases glycated hemoglobin HbA1c, a surrogate marker for diabetes mellitus.

[53] The low SHBG seen with premature androgenic alopecia is also associated with, and likely contributory to, insulin resistance,[54] and for which it still is used as an assay for pediatric diabetes mellitus.

[58] Patients with Laron syndrome, with resultant deficient IGF, demonstrate varying degrees of alopecia and structural defects in hair follicles when examined microscopically.

[60] SHBG association with fasting blood glucose is most dependent on intrahepatic fat, which can be measured by MRI in and out of phase imaging sequences.

This is not intuitive, as testosterone and its peripheral metabolite, DHT, accelerate hair loss, and SHBG is thought to be protective.

[73] The testicular secretion of testosterone perhaps "sets the stage" for androgenic alopecia as a multifactorial diathesis stress model, related to hormonal predisposition, environment, and age.

[89] Other treatments include tretinoin combined with minoxidil, ketoconazole shampoo, dermarolling (Collagen induction therapy), spironolactone,[90] alfatradiol, topilutamide (fluridil),[87] topical melatonin,[91][92][93] and intradermal and intramuscular botulinum toxin injections to the scalp.

[94] There is evidence supporting the use of minoxidil as a safe and effective treatment for female pattern hair loss, and there is no significant difference in efficiency between 2% and 5% formulations.

The types of devices (hat, comb, helmet) and duration did not alter the effectiveness,[100] with more emphasis to be placed on lasers compared to LEDs.

[108] Factors that determine efficacy include amount of sessions, double versus single centrifugation, age and gender, and where the PRP is inserted.

[109] Future larger randomized controlled trials and other high quality studies are still recommended to be carried out and published for a stronger consensus.

The authors of the study said the next research step is to introduce the microRNA into the stem cells using nanoparticles applied directly to the skin, with the goal of developing a similar topical application for humans.

[119] Female androgenic alopecia has become a growing problem that, according to the American Academy of Dermatology, affects around 30 million women in the United States.

[16] Biologists have hypothesized the larger sunlight-exposed area would allow more vitamin D to be synthesized, which might have been a "finely tuned mechanism to prevent prostate cancer" as the malignancy itself is also associated with higher levels of DHT.

[125] Many myths exist regarding the possible causes of baldness and its relationship with one's virility, intelligence, ethnicity, job, social class, wealth, and many other characteristics.

have put forward the idea that weight training and other forms of exercise increase hair loss in predisposed individuals.

Additionally, because hair loss is progressive and free testosterone declines with age, a male's hairline may be more indicative of his past than his present disposition.

[133] Animal models of androgenic alopecia occur naturally and have been developed in transgenic mice;[134] chimpanzees (Pan troglodytes); bald uakaris (Cacajao rubicundus); and stump-tailed macaques (Macaca speciosa and M. arctoides).

Male lions may have heightened levels of testosterone, which could explain their reputation for aggression and dominance, indicating that lack of mane may at one time have had an alpha correlation.

In infancy the hairline starts at the top of the supraorbital ridge, but slowly recedes after puberty to create the appearance of a small forehead.