Anti-fungal nail polish works by delivering an anti-fungal agent into the bed of the nail, killing the fungus that grows under the nail itself. Some polishes, such as Penlac, contain the active ingredient ciclopirox, a prescription anti-fungal that is sometimes used in the treatment of dermal fungal infections like ringworm.
Nail polishes that contain ciclopirox work by inhibiting certain enzymes in the fungal cells, causing the fungus to die. Because nails grow relatively slowly, the patient generally needs to continue using the nail polish for several months to allow the affected part of the nail to grow out, giving the fungus less chance to regrow.
Penlac nail polish should be applied once per day, usually at bedtime. The patient applies the polish to the entire surface of the nail, as well as the areas of skin that are in immediate contact with the nail. The polish should be allowed to dry for no less than 30 seconds and then the affected area kept dry for at least eight hours after application.
Polish builds up on the nail after multiple applications, so once every seven days, the patient must use an alcohol solution to remove the built-up polish. Prescription durations may vary depending on the severity of the fungal infection; however, it may take six months to a year before the infection is fully healed.