hmmmm i don't know about
absolutely no damage, but i attribute my hair's good health to bettering my diet, not straightening with heat often, learning to comb/detangle properly, protective styling, using mayo and eggs for protein/cholesterol once a month, from using henna a few times in the past, and i cannot say this enough - MOISTURE MOISTURE MOISTURE!!! i love co-washing for this but also i have just tried the Afro Detangler from growafrohairlong.com and i love it... for my hair and my son's (a tighter 4a texture with a lot more 4b mixed in).
awesome stuff.
i mostly let my hair do it's own thing and that keeps it happy.