Hair growth and shedding are cyclical. The growth cycle is divided into three phases: the anagen, catagen and telogen. Normal hair about 90% to 95% of the hair follicles in the anagen phase, 1% into the regression phase, 5% to 10% for the resting phase, to the end of the resting period, the hair is shed, the hair follicles into the next growth cycle. The duration of the anagen phase determines the length of the hair. The hair growth period is about 2 to 6 years, the regression period is 2 to 3 weeks, and the resting period is 2 to 3 months. The ratio of anagen to resting follicles determines the thinning of the hair. Hair loss occurs clinically when the anagen phase is shortened and the number of resting hair follicles increases. There are two most common types of alopecia areata, namely androgenetic alopecia and alopecia areata, and we would like to briefly introduce the progress of their treatment. I. Treatment of androgenetic alopecia Androgenetic alopecia was once called “seborrheic alopecia” or “early baldness”. It can occur in both men and women. However, the clinical manifestations are different. Male pattern androgenetic alopecia starts from the sideburns on both sides of the forehead and gradually decreases in the shape of an M. Eventually, most or all of the hair is lost. There are also cases in which the forehead, sideburns and the top of the hair fall out at the same time, or from the top, but the occipital hair is generally not affected. Female-pattern androgenetic alopecia is usually characterized by thinning hair on the top, while the frontal area remains unchanged. It occurs in both males and females between the ages of 12 and 40 and is polygenic. The pathogenesis of this disease, in addition to genetic factors, is closely related to the metabolism of androgens. In androgenetic alopecia, the amount of G ketone converted to dihydro-G ketone increases due to the increased level of type II 5α-reductase in the hair root sheath outside the hair follicle and in the dermal papillae. Dihydro-G ketone is a strong androgen that cannot be converted to estrogen by aromatase, while the affinity of dihydro-G ketone for androgen receptors is five times greater than that of G ketone. Dihydro-G ketone enters the nucleus after binding to androgen receptor, and controls the expression of hair growth genes in the nucleus, as a result, hair follicles are miniaturized, the growth period is shortened, and hair becomes fine and downy to thinning. (a) Treatment of male pattern androgenetic alopecia: The treatment of male pattern androgenetic alopecia includes internal or external drug therapy, surgical treatment and Chinese herbal medicine therapy, etc. This article only introduces the internal and external drug therapy. Finasteride is an inhibitor of 5α-reductase, which is well absorbed after oral administration and quickly reduces the level of dihydrogen G ketone in the serum and scalp by 60% to 70%, and reduces the amount of dihydrogen G ketone in the hair follicles, thus preventing the scalp hair follicles from becoming smaller and reversing the process of hair loss. Its usage is 1 mg orally daily [trade name: propecia], which was approved by the FDA in December 1997 for the treatment of male pattern androgenetic alopecia. According to three randomized, double-blind, placebo-controlled clinical studies, of 1879 male patients aged 18 to 41 years with mild to moderate androgenetic alopecia, 1553 of whom had alopecia on the top of the head and 326 had alopecia on the forehead, there was a statistically significant difference in the number of hairs that increased in the former group after one year of finasteride 1 mg daily compared to the placebo group. In the group of those receiving placebo for topical alopecia some switched to finasteride while others continued to apply placebo, and by the end of the second year, the hair number continued to increase at the same level in the group that continued to take finasteride, and the number of hairs decreased in those who switched from finasteride to placebo, while the number of hairs increased in those who switched from placebo to finasteride, and the photographic comparison showed that 66% of the hair growth in the finasteride group covered more scalp area than before The photo comparison showed that 66% of the finasteride group had a significant increase in hair growth covering the scalp area compared to only 7% of the control group. This indicates that finasteride treatment not only increased the number of hairs, but also their length, diameter and pigmentation, so the area covering the scalp was significantly improved. Kaufman reported the results of 1553 cases treated with finasteride for 5 years, showing that more than 90% of the patients stopped losing hair according to the photographic rating, compared to 25% in the placebo group. Based on hair counts, 65% of patients in the finasteride treatment group had increased hair numbers, and even in those who did not, no further hair loss was seen, whereas in the placebo group there was no increase in hair numbers in one case and progressive hair loss was seen. Regarding the safety of long-term treatment with finasteride, the following drug-related adverse effects were observed at one year: decreased libido (1.8% in the finasteride group and 1.3% in the placebo group), impotence (1.3% in the finasteride group and 0.7% in the placebo group) and decreased ejaculation (1.2% in the finasteride group and 0.7% in the placebo group). Only 7 (1.3%) of the 547 cases with five years of continuous finasteride use discontinued the drug due to drug-related sexual adverse effects. Most of these side effects tapered off with continued treatment. The discontinuation of treatment then subsided after a few days or weeks. 2, minoxidil (minoxidil) topical minoxidil can prolong the hair growth period, so that the development of miniaturized hair follicles increased. According to experimental research, in the in vitro culture of hair follicles, the addition of minoxidil can increase the growth time of cultured hair follicles. Hair follicle hepatocyte growth factor and vascular endothelial cell growth factor are the two main growth factors of hair papillae, which have an important role in regulating the hair growth cycle. lachger et al. reported that minoxidil upregulated the expression of vascular endothelial cell growth factor mRNA in hair papillae cells. Therefore, it is believed that minoxidil plays an important role in the treatment of hair loss by stimulating and maintaining hair follicle growth and hair papilla blood vessel formation and function through the above cytokines. In 1988, the FDA approved the topical application of 2% minoxidil solution for the treatment of male pattern androgenetic alopecia. 2294 male patients aged 18 to 50 years with mild to moderate topical alopecia were treated for 12 months, and the number of hairs in the minoxidil group increased, and the diameter of the hair grown in the minoxidil group also increased as demonstrated by histology. Later Trancik et al. applied 5% minoxidil, 2% minoxidil and placebo control in 393 cases of male pattern androgenetic alopecia after 48 months of treatment, and the hair count was 45% higher in the 5% minoxidil group than in the 2% minoxidil group and 5 times higher than in the placebo group. Price et al. conducted a double-blind controlled study of 2%, 5% minoxidil, placebo and no treatment groups, and observed a total of 96 weeks, both 2% and 5% minoxidil topical in the promotion of hair growth and increase the effectiveness of hair have higher than the placebo group and no treatment group, the efficacy occurred mostly in 2 to 3 months after treatment, but After 4 weeks of follow-up after 96 weeks of discontinuation, hair loss started to occur again, this result also indicates that minoxidil topical treatment is the role of promoting hair growth. At the beginning of the topical treatment with minoxidil, the number of hairs that promote miniaturization increases dramatically, while the follicles of these hairs are still in a short growth cycle, so patients treated with topical minoxidil often complain of a temporary increase in hair loss at 12 weeks after treatment. Minoxidil topical treatment for hair loss is applied topically twice daily at approximately 1 mL each time, directly onto the scalp and spread with the fingers. Because the efficacy is often seen after 2 months of application, it should be explained to the patient at the beginning of treatment to adhere to the medication and maintain it until the efficacy is seen. Minoxidil topical side effects, mainly irritation reactions, that is, the application site occurred dry, flaking, itching and redness. 2% solution incidence is about 7%, 5% solution incidence is higher than 2% solution. The occurrence of these side effects is related to the concentration of propylene glycol in it. The occurrence of allergic contact dermatitis or photomimetic contact dermatitis has also been reported. Another skin side effect is hypertrichosis, which occurs less frequently in men. Either 5% or 2% minoxidil solution, applied twice daily at 1 mL each time, does not cause changes in blood pressure, pulse rate or body weight. Because according to the pharmacokinetic study, the application of 5% minoxidil solution, the average value of 1.2ng/mL measured in serum, far below the minimum amount of 20.0ng/mL required to cause hemodynamic changes in blood pressure and pulse.