Cocamidopropyl hydroxysultaine (aka, coco hydroxysulfaine).
EWG Hazard Score:
What is it:
Cocamidopropyl hydroxysultaine is similar to cocamidopropyl betaine. It is a synthetic detergent used also as a foam booster, thickener, and anti-static agent.
What are it's risks:
Like cocamidopropyl betaine, it can be a strong skin allergen. (Source)
There is only ONE published study regarding the safety of this ingredient. The MSDS sheet is also not made public. Although the database scores it as a 0, it doesn't necessarily mean that it's safe--it's just means that there is no data on the ingredient. So, while it doesn't have a history of being harmful, it also doesn't have a history of being safe. If you have skin sensitivies, eczema, reactions, and such, I would personally suggest avoiding this ingredient.