Which ingredient is known for strengthening nails?

Formaldehyde is widely recognized for its use in strengthening nails. In nail products, it acts as a hardening agent that helps to improve the integrity of the nail structure, making it less prone to breakage and chipping. This ingredient works by forming a barrier on the surface of the nail, which can enhance durability and provide some level of protection against environmental factors that may weaken the nails.

While other options like mineral oil and oleic acid may offer moisture and conditioning benefits, they do not specifically contribute to strengthening the nails in the way that formaldehyde does. Guanine, while a nucleotide that plays a role in various biological processes, is not typically associated with nail strength. Thus, formaldehyde stands out as an effective choice for anyone looking to fortify their nails.