research Effects of Permanent Waving on Changes of Protein and Physicochemical Properties in Human Head Hair 3 citations , August 2008 in “PubMed” Repeated digital perming with sodium thioglycolate lotion significantly damages hair protein and structure.
research Effects of Permanent Waving on Changes of Protein and Physicomorphological Properties in Human Head Hair May 2009 in “International Journal of Cosmetic Science” Permanent waving damages hair protein and weakens hair, especially with repeated treatments using sodium thioglycolate.