Grey nails, or onychomycosis, is a fungal infection of the nail plate that results in a change in colour, accompanied by a change in the texture of the nail plate, which is brittle, lustrous and can be thickened and distorted, and falls under the category of nail dystrophy. However, nail dystrophy as a collective term for abnormal nail manifestations can be caused by a variety of etiologies, such as genetics, dermatological conditions, medications, trauma and infections. Grey nails usually develop unilaterally, with one nail initially being infected, but gradually multiple nails may become involved. There is often a history of tinea pedis (foot fungus) before the onset of the disease. A fungal microscopy can be performed to help clarify the diagnosis. However, it is important to note that fungal infections can occur secondary to other causes of nail dystrophy, so it is important to actively and carefully analyse and search for the cause.