1. Product literature. Covington, KY: Ashland Inc., www.ashland.com.
2. History of polymers in hair care (1940-Present);Lochhead;Cosm Toil,1988
3. Preservative directory. www.thefreelibrary.com.
4. Preservative directory. www.Happi.com.
5. US pharmacopeia (USP<51>).