Methylcellulose is a modified natural carbohydrate polymer derived from cellulose.
It significantly improves skin feel and viscosity.
The Environmental Working Group (EWG's) Skin Deep is the world's largest personal care product safety guide. They rate ingredients according to their hazard score on a 0-10 scale from low to high hazard. For example, they give water a score of 0.
Accordingly they have rated Methylcellulose with a score of 1.