I know it's been debated before, but I came across some text from a medical book that I thought I would post. As background, PPG is the chemical in some minoxidil products that causes skin irritation. PPG-free products (like Dr. Lee's PPG-free solutions and Rogaine Foam) typically use glycerin instead of PPG.

The book is called Fishers Contact Dermatits. It has nothing to do with hair loss. It has a section about PPG as a skin irritant and within that section has a paragraph titled "Glycerin vesus Propylene Glycol"...here's the text and the link:

"Generally, it is agreed that glycerin is much less active than PG in producing primary irritant and allergic reactions. It is claimed, however, that glycerin is a less desirable solvent than PG. Also PG has better permeation through the stratum corneum, probably because it has different solvent properties(i.e., propylene glycol is more lipid soluble than glycerin). Becuase of these superior solubility properties, PG is preferred over glycerin in many pharmaceutical and cosmetic perparations..."

http://books.google.com/books?...&ct=result&resnum=10

I used Rogaine with PPG for about 15 years and have used PPG-free stuff for last couple. I can't really use PPG anymore because the irritation just got so bad and continued to get worse the longer I used it. I personally feel the PPG-free stuff isn't near as effective as solutions with PPG.

Just my two cents worth and what I've found to be the case for me. I have no proof to back up my opinion.

Excellent post. I've wondered about this for a long time. There seem to be at least some reputable people who believe that PPG is very important in minoxidil. I suppose for those who have a reaction, it's better to at least be able to use the minoxidil in a different formulation, rather than not be able to use it at all.

My minoxidil solution, made on local pharmacy, has both ingredients: Propylene Glycol and Glycerin