Nail cosmetics: allergies and irritations.

Recent precise figures are not available for the number of adverse reactions related to the use of nail care products. Reactions to nail cosmetic procedures may be divided into reactions at the site of application to the nail itself and ectopic reactions, when the hand transfers a small amount of nail cosmetic to other areas of the skin. Fingernail coatings encompass two types: coatings that harden upon evaporation (nail enamel, base coat, top coat); and coatings that polymerize (sculptured nails, light-curing gels, preformed artificial nails, nail mending and nail wrapping). The test battery enables us to distinguish allergic reactions from irritant reactions. Interestingly, some reactions, such as distant allergic contact dermatitis, are more frequent with nail enamel than with coatings that polymerize. On the other hand, the latter are greater offenders in the nail area. Nail hardeners may just be modified nail enamels containing nylon fibers, acrylate resin and hydrolyzed proteins. Others may contain up to 5% formaldehyde tissue fixative (which can have adverse effects on the nail), but are designed in the US to be applied only to the free edge of the nail while the skin is shielded. Caution is necessary in interpreting formaldehyde patch testing reactions.