Which type of nail disorder may be treated at the salon?

Onychophagy, commonly known as nail biting, is a nail disorder that can be addressed effectively in a salon setting. Manicurists are trained to create a supportive environment that encourages clients to stop biting their nails. Treatments can include manicures that emphasize nail care, applying bitter-tasting nail polishes designed to deter biting, and providing advice on maintaining nail health.

The other conditions, while they may be important for a client to understand, typically require more specialized treatment. Hyponychium refers to the skin under the free edge of the nail and does not require specific treatment in a salon. Onycholysis is the separation of the nail from the nail bed, which can indicate underlying issues that need to be diagnosed by a medical professional. Lastly, the eponychium is the cuticle, involved in nail growth, and while it can be managed in a manicure, it cannot be "treated" in the conventional sense for conditions. Therefore, onychophagy stands out as a disorder suitable for salon intervention.