Foreign literature reports on an open preliminary study of the treatment of androgenetic alopecia with botulinum toxin type A. In this ethically approved study, 50 male patients aged 19 to 57 years with Norwood/Hamilton classification of II to IV alopecia were enrolled. The study lasted 60 weeks and consisted of one 12-week informal period and two 24-week treatment cycles. Subjects were injected with 150 units of botulinum toxin (5 units per 0.1 ml of saline) within the muscles surrounding the scalp, which included the frontalis, temporalis, periaqueductalis, and occipital muscles. More than 30 injection sites in these muscles were injected with the same dose of botulinum toxin. The primary outcome measure was the alteration of hair follicles within a fixed 50px range according to the method described by Canfield. Secondary outcome measures included hair loss, counting of hairs lost by subjects collected from the occipital head and a defined questionnaire asking subjects about validity. Statistical analysis was limited to a paired t-test. 40 subjects completed this study with no side effects. The treatment response rate was 75%. The mean hair count for the entire group was statistically significant (p < 0.0001) and increased by 18% at week 48 compared to baseline, similar to the results of Propecia (Merck, Whitehouse Station, N.J.). Hair regrowth was seen in some subjects (Figure 1). Secondary outcome measures were also significantly improved. The reduction in hair loss and the increase in hair count did not show a statistical correlation. This suggests that a longer terminal hair resting period does not account for the increase in hair count. Possible rationale: The scalp is like a drum skin surrounded by tense muscles. The long-term action of these muscle groups - the frontal, occipital and periauricular muscles and to a lesser extent the temporalis muscle - can make the scalp tense. Because the blood supply to the scalp enters from all around, reduced blood flow manifests itself most predominantly at the ends of the blood vessels, especially at the top of the head and the top of the forehead. Sparse hair growth in these areas shows relatively low oxygenation, shows less capillary reperfusion, and also shows high levels of dihydrotestosterone. Conceptually, Botox relaxes the scalp and reduces pressure on the vascular system that crosses it, thereby increasing blood flow and oxygen concentration. The enzyme that converts testosterone to dihydrotestosterone is oxygen demanding. In a low oxygen environment, the conversion of testosterone to dihydrotestosterone is beneficial, but in a high oxygen environment, more testosterone is converted to estradiol. Thus blood flow may be a major determinant of hair follicle health. Botox injections can directly alter this variable, leading to a reduction in hair loss and regrowth of new hair in some men with androgenetic alopecia. Literature images: Our case.