 What is HEMA? HEMA is short for hydroxy-etoxymetacrylate, so HEMA is in fact an acrylate monomer. Monomer means one, so it's a short molecule and it's used in the polymerization process of UV curing nail enhancement products. Since HEMA is a small molecule, it is more reactive and it can cause allergies for overexposure for a long period of time. For instance people like dentists or nail technicians who come in contact with HEMA need to be careful. Also their clients, which HEMA is used which is maybe not cured, need to also be protected from this. A fully cured acrylate in which HEMA was used is totally harmless. Think about a contact lens that you put in your eye. So the big responsibility is actually in your hands and that is to make sure that all UV gels that you use, lead gels or UV gels are always fully cured to avoid any form of sensitization.