How to Wash Your Head, 1612

"You shall finde it wonderfull expedient, if you bath your head foure times in the yeare, and that with hot lee made of ashes. After which, you must cause one presently to poure two or three gallons of cold fountain water upon your head. Then let your head be dryed with cold towels. Which sodaine pouring downe of cold water, although it doth mightily terrifie you, yet nevertheles, it is very good, for therby the naturall heate is stirred within the body, baldnesse is kept backe, and the memory is quickened. In like manner, washing of hands often, doth much availe the eyesight." 

William Vaughan, Approved Directions for Health (1612)

Pouring water on your head sure is terrifying! But the dreaded quarterly headwashing has its benefits. Best practices!

How to Treat Baldness, 13th century

"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 (c. 13th century)

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?