A horizontal indentation in the middle of the nail may be related to a variety of factors, such as onychomycosis, lack of micronutrients, eczema, psoriasis and other diseases caused by the patient under the guidance of a doctor to clarify the specific cause of the disease and later treatment. 1. Inguinitis: Inguinitis is formed when the nail groove and surrounding tissues become infected. Chronic inguinitis can induce changes in nail morphology, with bulges and grooves appearing. Mild infections can be treated with topical antibiotic medications, such as mupirocin ointment and erythromycin ointment. In severe cases, the nail plate needs to be removed. 2. Lack of trace elements: trace elements are necessary components to ensure the normal growth of nails, when the body lacks trace elements, it can cause changes in nail morphology, which can be improved by oral multidimensional elemental tablets. 3. Eczema, psoriasis and other related skin diseases: when related skin diseases involve the nails, it may also lead to nail damage. At this time, it is recommended that the patient actively treat the primary disease, and as the primary disease improves, the nail damage will also improve. When a horizontal concave line appears in the middle of the patient’s nails, it is recommended to go to a regular hospital for examination in a timely manner, and under the guidance of a professional doctor to carry out active treatment, the specific use of medication should be in accordance with the doctor’s instructions.