Hair loss is starting to exist in young men in their twenties. This suggests that there is a strong environmental component.
In traditional societies, hair loss only existed among older men. If you look at men in traditional societies, only the older men have them, but even then, their hair loss isn't as substantial compared to their equivalent men in industrialized societies. This suggests that our increased prevalence of hair loss is predominately environmental, not genetic or hormonal.
Finasteride side effects
Finasteride decreases DHT. But DHT itself is anti-estrogenic and causes fat loss.
Finasteride could cause loss of libido even when males are taken off the drug. Finasteride could also cause gynecomastia due to its progestogenic effects.
Stress hormones and hair loss
Danny Roddy's book, Hair Like a Fox, is a book about hair loss. This book is based on the research by Ray Peat. The book goes over some of the hormones associated with balding, including cortisol, adrenaline, estrogen, serotonin and prolactin. Animal experiments have shown that cortisol and prolactin induces hair loss. Some anti-depressants and anti-psychotics could cause hair loss because they raise serotonin. Insufficient protein and low thyroid function could also cause hair loss.
Estrogen and hair loss
Danny Roddy's book also suggests it is not testosterone or DHT which causes hairloss, because older men have less of these androgens. It's because testosterone could be converted to estrogen by the enzyme aromatase; older and disease people have both a higher expression of aromatase and decreased capacity to excrete estrogen due to impaired liver function. Pregnant women have greater progesterone which antagonizes estrogen. Some women also suffer from "male pattern baldness" but some of them grew new hair when pregnant due to increased progesterone. Finasteride has some effects similar to progesterone.
Castrated men don't go bald because they don't produce any testosterone which could aromatize into estrogen. So castrated men have low estrogen to begin with.
It has been suggested that anabolic steriods could cause balding because such steriods could be aromatazed into estrogen.
See also: How to lower estrogen
Red light therapy (shining red light in your scalp) has shown that it helps you to regrow your hair. Also there are studies on tocotrineols (unsaturated vitamin E) showing that they help to regrow scalp hair. Vitamin E is anti-inflammatory and is similar to aspirin.