Topical DHT Blockers...help!

I'm a 30 yr old male with moderately low testosterone levels and have begun taking some natural supplements to boost them. However, I have read that higher testosterone and dht levels often accelerate a person's MPB. My hair loss is not very pronounced yet but I notice a receding hairline and generally very thin hair everywhere except the sides (looks like the outline for future MPB to me). If I want to continue using these supplements and also try to maintain my hair would topical DHT blockers be the best bet? If so which ones should I consider trying? Also do topical DHT blockers block the effects of DHT on the scalp only or do they have the effect of blocking DHT in the body as a whole? Thanks very much for any help/feedback!

Dee