Hollow fingernails are also clinically known as nail bed separation, which may be caused by non-disease factors such as chemical agent stimulation, or may be related to pathological factors such as trauma, skin diseases, infection, tumors underneath the nails and so on. 1. Non-disease factors: such as long-term contact with detergents, laundry detergents and other irritating substances or frequent manicures, etc. can cause irritation and damage to the nail bed, resulting in separation of the nail bed. 2. Pathologic factors (1) Traumatic injury: such as finger squeezing or using sharp instruments to clean up the dirt stuck in the nail and other nail injuries, thus causing separation of the nail bed, manifested in the symptom of empty nails. (2) Skin diseases: such as lichen planus, psoriasis, atopic dermatitis, etc. Although it involves the skin, it also invades the nails, which causes the separation of nail beds and manifests as the symptom of empty nails. (3) Infections: such as fungi, viruses, bacteria and other infections, invade the nail bed gap, rapid reproduction, can further appear nail loosening, nail bed separation symptoms, manifested as nails become empty. (4) Tumor under the nail: if there are hemangioma, fibroma, malignant squamous cell carcinoma under the nail, the chance is not high, but especially malignant skin cancer can cause separation of the nail bed, which will show the symptom of empty nail. It is recommended to go to the hospital in time to find out the cause of empty fingernails, so as not to delay the condition.