Infections may involve the nail itself, the bed under the nail, or the skin around the nail. Most nail infections are fungal (onychomycosis), but bacterial and viral infections can occur. Bacterial infections may occur in the cuticle or nail folds (paronychia).
Onychomycosis is a fungal infection of the nails.
About 10% of people have onychomycosis, which most often affects the toenails rather than the fingernails. The fungus can be acquired through contact with an infected person or contact with a surface such as a bathroom floor where the fungus is present. The fungus commonly occurs as part of an infection called athlete's foot (see Fungal Skin Infections: Athlete's foot). Older people, people who have diabetes, and people with poor circulation to the feet are particularly prone to fungal infections.
Infected nails have an abnormal appearance but are not itchy or painful. In mild infections, the nails have patches of white or yellow discoloration. A chalky, white scale may slowly spread beneath the nail's surface. In more severe infections, the nails thicken and appear deformed and discolored. They may detach from the nail bed. Usually, debris from the infected nail collects under its free edge.
Diagnosis and Treatment
A doctor usually makes the diagnosis based on the appearance of the nails. To confirm the diagnosis, the doctor may need to examine a sample of the nail debris under a microscope and culture it to determine which fungus is causing the infection.
Fungal infections are difficult to cure, so treatment depends on how severe or bothersome the symptoms are. If treatment is desired, the doctor may prescribe itraconazole or terbinafine taken by mouth. Although these drugs are taken for a long time (about 3 months), they remain bound to the nail plate and continue to be effective after use of the drug is stopped. Ciclopirox, an antifungal drug that is placed in a nail lacquer, is not very effective when used alone but can improve the cure rate when used in addition to drugs taken by mouth, particularly in resistant infections. Ciclopirox can be of some help to people who cannot take oral drugs for other health reasons.
To limit the possibility of a relapse, the nails should be kept trimmed short, the feet should be dried after bathing, absorbent socks should be worn, and antifungal foot powder may be used. Old shoes may harbor a high density of fungal spores and, if possible, should not be worn.
Paronychia is infection of the cuticle.
Paronychia is usually acute, but chronic cases can occur. In acute paronychia, bacteria (usually Staphylococcus aureus or streptococci) enter through a break in the skin resulting from a hangnail, trauma to a nail fold (the fold of hard skin overlapping the sides of a nail), loss of the cuticle, or chronic irritation (such as that from water and detergents). Paronychia is more common in people who bite or suck their fingers. In toes, infection often begins at an ingrown toenail (see Nail Disorders: Ingrown Toenail).
Paronychia develops along the nail margin (the sides and base of the nail fold). Over the course of hours to days, people with paronychia develop pain, warmth, redness, and swelling. Pus usually accumulates under the skin along the nail margin and sometimes beneath the nail. Rarely, mainly in people who have diabetes or other disorders that cause poor circulation, infection penetrates deep into the finger or toe and can threaten the digit or, in extreme cases, the limb.
The doctor makes the diagnosis by examining the affected finger or toe. In its earliest stage, paronychia may be treated with an antibiotic taken by mouth (such as dicloxacillin, cephalexin, or clindamycin) and frequent warm soaks to increase the blood flow. If pus accumulates, it must be drained. The doctor numbs the finger or toe with a local anesthetic (such as lidocaine) and lifts up the nail fold with an instrument. Cutting the skin is usually unnecessary. A thin gauze wick is inserted for 24 to 48 hours to allow the area to drain.
Chronic paronychia is recurrent or persistent inflammation of the nail fold, typically of the fingers.
Chronic paronychia occurs almost always in people whose hands are chronically wet (for example, dishwashers, bartenders, and housekeepers), particularly if they have diabetes or an impaired immune system. The yeast Candida is often present, but its role in causing chronic paronychia is unclear because eliminating the yeast completely does not always cure the condition. Chronic paronychia may be the result of an irritant skin inflammation (dermatitis) in addition to colonization with Candida.
The nail fold is painful and red as in acute paronychia, but pus usually does not accumulate. Often there is loss of the cuticle and separation of the nail fold from the nail plate. A space then forms that allows irritants and microorganisms to enter. The nail can become distorted.
The doctor makes the diagnosis by examining the affected finger.
Keeping the hands dry and protected can help the cuticle reform and close the space between the nail fold and nail plate. Gloves or barrier creams are used if water contact is necessary. Corticosteroid creams applied to the nail may be helpful. Antifungal treatments are helpful only in reducing fungal organisms. Applying a solution of thymol in ethanol several times a day to the space formed by loss of the cuticle aids in keeping the space dry and free of microorganisms.
Green Nail Syndrome
Green nail syndrome is infection with Pseudomonas, a type of bacteria.
Green nail syndrome is caused by an infection with Pseudomonas, species. It usually develops in people who have onycholysis and whose hands are often in water. The nail in the area of onycholysis becomes greenish in color. The area can be treated by soaking in a 1% acetic acid solution twice a day or by trimming back the nail and treating the area with an antibiotic solution.
Verruca vulgaris is common warts.
Verruca vulgaris is caused by infection with human papillomavirus and frequently infects the cuticle and sometimes the area beneath the nail. Nail biting (onychophagia) can spread this infection. Warts in these areas are especially difficult to treat. Freezing (cryotherapy) with liquid nitrogen may be effective.
Last full review/revision August 2007 by Wingfield E. Rehmus, MD, MPH