What is a nail strengthener?

Your nails are made of keratin, the same protein as hair. Most brush-on nail strengtheners contain protein and are formulated to harden nails over a period of time. Other common ingredients include calcium, vitamins and botanicals. Some strengtheners, such as those that contain formaldehyde, actually penetrate into the nail plate to strengthen nails from the inside. Other hardeners, liquid wraps, contain tiny fibers of a fabric that coat nails for extra thickness.