Sodium Lauryl Sulphate (SLS). I'm familiar with avoiding this additive found in many soaps and skin products as it irritates my girlfriends skin. Because of this we only buy soaps/ shampoo's without this compound.
A study has shown that if creams used to treat the skin condition eczema contain SLS, it could make the eczema worse.
There is a thin layer of lipids on our skin that protects it, retains moisture, and helps to reduce the absorption of chemicals into the skin.
SLS reduces the thickness of this protective layer. People with eczema already have compromised skin, and SLS could irritate their skin further.
Effect of Aqueous Cream BP on human stratum corneum in vivo - Tsang - 2010 - British Journal of Dermatology - Wiley Online Library