Which of the following nail diseases cannot be treated in a salon?

Onychocryptosis, commonly known as an ingrown nail, cannot be treated in a salon setting because it often requires medical intervention. This condition occurs when the edge of the nail grows into the surrounding skin, leading to pain, swelling, and potential infection. Professional treatment by a podiatrist or dermatologist is usually necessary to manage the condition properly, as they can deliver the appropriate medical care, including possible surgical intervention or prescription medications to prevent infection.

Other nail conditions such as onychomycosis (a fungal infection), onycholysis (the separation of the nail from the nail bed), and onychomadesis (the shedding of a nail) may sometimes be addressed within a salon, usually with proper sanitation and client consultation. While skilled professionals can manage symptoms or provide cosmetic support for these conditions, onychocryptosis specifically requires the expertise found in a medical environment, as dealing with the underlying infection and potential complications is crucial for effective treatment.