The topic of 'Hair Biology' is covered in detail across the two podcast episodes provided.

The first episode, "Why do we go bald?", explores the biological reasons behind human baldness, including the role of hair follicles and hormones like testosterone and DHT.

The second episode, "The Science of Healthy Hair, Hair Loss and How to Regrow Hair", goes in-depth into the biology of hair growth, including the three phases of hair growth (anagen, catagen, telogen) and the factors that regulate these phases.