Which monomer liquid is not recommended for use on nails due to safety concerns?

Methyl methacrylate is the monomer liquid not recommended for use on nails due to significant safety concerns. This compound can pose various health risks, including potential allergic reactions and respiratory issues. It has been associated with adverse effects due to skin irritations and its strong odor, which can cause discomfort during application.

From a regulatory perspective, many professional nail organizations have cautioned against the use of methyl methacrylate in nail products because of its potential to damage the natural nail and surrounding skin. It is also more likely to cause severe allergic responses compared to other monomers. Thus, as a safer alternative, products formulated with ethyl methacrylate, isobutyl methacrylate, and butyl acrylate are preferred in professional nail applications, as they are generally better tolerated and have a lower risk profile for clients and nail technicians alike.