I had a major problem with scalp itch after trying the Herbal Essence Set Me Up gel. I finally decided that it must be the particular polyquanternium. After doing a low-poo that didn't solve the problem, then doing a baking soda cleanse (followed by lemon juice mixed into my conditioner to restore the normal pH of my hair), which solved the problem until I added the HESMU gel again, and I ended up having to do the low-poo then baking soda cleanse again.

I have used the Suave Naturals conditioners for co-washing since I went CG, and had no problems with them. Your mileage may vary, but it can be really helpful to sleuth this out, so that you can avoid the offending ingredient. The way hair care product formulas keep changing, knowing what to avoid (and what to look for) can be a huge help.
Peace,
Morgan

Baby Fine 3B, low porosity, normal density and elasticity
CGing since July 2008