What is the key ingredient commonly found in nail hardeners?

The key ingredient commonly found in nail hardeners is methylene glycol. This compound is a derivative of formaldehyde that acts as a hardening agent, helping to strengthen the nails and prevent breaking or splitting. Methylene glycol works by forming a protective layer on the surface of the nail, which enhances resilience and durability.

While formaldehyde is also known to be used in some nail products for its strengthening properties, methylene glycol is considered a safer and less harsh alternative, making it more commonly included in modern formulations for nail hardeners.

Acetone is primarily recognized as a solvent in nail polish removers, and calcium carbonate, while beneficial for overall nail health, does not serve the same purpose as a hardening agent in this context.