How to Treat Baldness, 13th century

manuscript illustration of tonsured clerics pointing at each other in historiated initial “You’re bald.” “No, you’re bald.”
BL Royal 6 E VII, f. 197 (14th c.)

By frequently rubbing your bald spots with ground onions, you will be able to recover the charm of your head.

Regimen sanitatis salernitanum

This piece of advice is pretty cagey. Does the remedy actually cause your hair to return, or does an onion-greased scalp count as charming?