Low Testosterone Does Not Cause Hair Loss
Low testosterone (hypogonadism) does not cause scalp hair loss; in fact, testosterone deficiency may contribute to hair thinning, and testosterone replacement therapy can improve scalp hair growth in androgen-deficient individuals. 1
The Paradoxical Relationship Between Testosterone and Hair Loss
Testosterone Deficiency and Hair Thinning
Women with androgen deficiency who received subcutaneous testosterone therapy reported significant improvement in scalp hair growth, with 63% of those experiencing hair thinning prior to treatment reporting hair regrowth on testosterone therapy. 1
Baseline serum testosterone levels were significantly lower in women reporting hair loss prior to therapy compared to those without hair loss (P=0.0001), suggesting that low testosterone may contribute to scalp hair thinning rather than cause it. 1
No patient receiving testosterone therapy reported scalp hair loss as a result of treatment, challenging the presumed role of testosterone in driving hair loss. 1
The beneficial effect of testosterone on scalp hair growth is thought to be due to an anabolic effect of testosterone on hair follicles, promoting hair growth rather than hair loss. 1
The Role of Dihydrotestosterone (DHT), Not Testosterone
Androgenetic alopecia (male and female pattern baldness) is driven by dihydrotestosterone (DHT), not testosterone itself. DHT is formed through conversion of testosterone by the enzyme 5α-reductase within hair follicles. 2, 3
Women with female-pattern hair loss have increased production rates of testosterone but normal or below-normal production rates of DHT, unlike men with male-pattern baldness. 4
The local conversion of testosterone to DHT within hair follicles by 5α-reductase is what causes miniaturization of genetically susceptible hair follicles in androgenetic alopecia, not circulating testosterone levels. 2, 3
Clinical Implications for Hypogonadal Men
Men with testosterone deficiency may experience reduced body hair in androgen-dependent areas as part of the clinical presentation of hypogonadism, but this is distinct from scalp hair loss. 5
Testosterone replacement therapy in hypogonadal men improves multiple symptoms including sexual function, muscle mass, bone density, and well-being, but does not cause scalp hair loss. 5
The decreased facial and body hair seen in transgender women receiving feminizing hormone therapy (which lowers testosterone to <50 ng/dL) demonstrates that low testosterone reduces hair growth in androgen-dependent areas. 5
Important Caveats
Drug-Induced Androgen Deficiency
5α-reductase inhibitors (finasteride, dutasteride) used to treat male pattern baldness create a form of tissue-level androgen deficiency by blocking conversion of testosterone to DHT, which can have negative metabolic effects including fat accumulation in the liver, insulin resistance, and worsening erectile dysfunction. 6
These medications work precisely because they reduce DHT levels locally in hair follicles, not by reducing testosterone. 6, 3
Obesity as a Confounding Factor
Obese patients with low total testosterone often have normal free testosterone due to increased aromatization of testosterone to estradiol in adipose tissue, which is a confounding factor when evaluating testosterone deficiency. 7
Women with higher BMI were less likely to respond to testosterone therapy for hair regrowth (P=0.05), suggesting obesity may interfere with the anabolic effects of testosterone on hair follicles. 1
Clinical Bottom Line
If a patient presents with both low testosterone and hair loss, these are likely separate issues rather than causally related. The hair loss is most likely androgenetic alopecia driven by DHT sensitivity in genetically predisposed follicles, while the low testosterone represents a separate endocrine disorder requiring evaluation and potential treatment. 5, 7 Treating the testosterone deficiency will not worsen scalp hair loss and may actually improve it. 1