If you were already genetically predisposed to lose your hair (i.e. if your mom’s side has men [&/or women] with androgenic alopecia), testosterone of any origin (outside the body or naturally produced) can contribute to hair loss. It isn’t testosterone itself, but dihydrotestosterone (DHT), which testosterone may convert into. In comparison to injections, testosterone gel has an especially high rate of converting to DHT due to an abundance of DHT converting enzymes (5 alpha reductase) in the skin.

However, hair loss can have multiple hormonal causes (adrenaline, hypothyroidism, etc.) & non-hormonal causes. Even DHT’s role is complicated, as it *may* help the immune system in treating hair follicles on the scalp as foreigners, thereby causing hair loss as an autoimmune response. This is only one mechanism of hair loss.