Normal nails have a smooth and shiny surface. The reasons for nails with horizontal stripes include diseases, malnutrition, physical or chemical stimuli, and so on. 1. Disease: Nail lichen planus and nail fungus disease can be manifested by the appearance of horizontal lines on the nails. Eczema involving the nails can lead to nail separation, horizontal lines on the nails, and rough and uneven surface of the nails. 2. Malnutrition: due to insufficient nutritional intake or nutritional absorption disorders leading to nutritional inadequacy, nails grow at different speeds, appearing raised and sunken horizontal stripes. 3. Physical or chemical stimulation: It may be related to occupation, habit, etc. Frequent contact with hot water, laundry detergent, disinfectant, chemical reagents such as nail polish, etc., may lead to nail plate damage and the appearance of horizontal lines on the nails. Nails appear horizontal lines should be timely consultation, under the guidance of the doctor for treatment, daily attention to personal hygiene, avoid contact with irritating substances, pay attention to rest.