Thickening of the flesh under the nail cap may be caused by onychomycosis, onychomycosis, trauma and so on. 1. Onychomycosis: refers to nail lesions caused by dermatophytes invading the nail plate/nail bed. Clinical manifestations include thickening of the nail flesh or nail bed, discoloration of the nails, and unevenness. 2. Onychomycosis: Onychomycosis can be triggered by cutting nails too short, bacterial infection and abnormal nail growth. Inflammation stimulates the nail for a long time, which will lead to the proliferation of granulation tissue, thus showing nail flesh hyperplasia. 3. Trauma: external impact on the nail area may result in localized damage to the nail tissue, which may lead to nail flesh hyperplasia and the appearance of hyperplastic bulging of the nail flesh. The thickening of the flesh under the nail cap may also be caused by common warts, etc. It is recommended that the patient consult a doctor in a timely manner, make a clear diagnosis and follow the doctor’s instructions for treatment.