Onion extract isn't typically thought of as a DHT blocker, despite research suggesting it may encourage hair growth. Rather, onion extract may function by increasing blood flow to the scalp, supplying vital nutrients to the hair follicles, and lowering inflammation, all of which may tangentially promote the development of healthy hair. According to some research, 5-alpha reductase, the enzyme that turns testosterone into DHT, may be inhibited by onion extract. To verify its efficacy as a DHT blocker, more research is necessary.