Purpose of Use

• A nail hardener can help strengthen your fingernails. Nail hardeners work to make your nail plate harder. They also impact the nail plate to keep it from peeling or breaking. When you apply the nail hardener to your fingernails, the hardener impacts the nails by forming a film on them.
  
  

Surface Effect

• Some nail hardeners act on the surface of the nail plate without going deeper. For example, some nail hardeners contain protein, possibly in the form of collagen, and polish that form a coating on the surface of the nail. Collagen cannot penetrate the nail. Other such surface-acting nail hardeners contain nylon.
  
  

Penetrating Effect

• Nail hardeners can also act on nail keratin. This category of nail hardeners contains formaldehyde that makes the keratin stronger by forming links between keratin strands in the nails. This makes the nail plates harder and less likely to bend. The U.S. government allows up to 5 percent use of formaldehyde in nail hardeners.
  
  

Risk Factors

• Don’t use a nail hardener on nail plates that are brittle or already hard. Formaldehyde can harden brittle nails so much that they become rigid enough to break. Also note that formaldehyde can irritate your skin and cause allergies. The Professional Beauty Association advises that you protect your skin from such contact by using grease or oil. When you are not using the nail hardener, you should keep the bottle capped. Don’t continue using a nail hardener if you experience an adverse skin reaction, your nails split or your nail bed discolors.