Gray nails, also known as nail fungus or onychomycosis, are caused by fungal infection of the nail plate and under the nail. Fungal microscopy and sometimes fungal culture are the main tests for gray nails, and the cost of a simple fungal microscopy is about$20. If combined with micrographic examination, the cost is about$60. If combined with fluorescent staining, the cost is about 200 yuan. Sometimes when combined with a fungal culture, the cost is about another hundred dollars. After the diagnosis of gray nail, you need to take oral antifungal medication, usually for more than three months, and toenails for more than four months. During the medication period, you should not drink alcohol and have your liver and kidney functions checked regularly.