The appearance of horizontal texture on the nail cap of the thumb may be caused by local trauma, or it may be caused by certain diseases, such as nail fungus disease, psoriasis, anemia and so on. 1. Localized trauma: due to localized trauma affecting the nail matrix cells at the root of the nail, resulting in a short period of time in which the matrix cells are in a state of stagnant growth, and when growth resumes again, the nail may be left with a horizontal texture structure. 2. Nail fungus disease: Nail fungus disease refers to nail lesions caused by fungi invading the nail bed or nail plate, which is infectious. Mild nail fungus disease may be manifested as white spots on the nails or white streaks, and in severe cases, it may invade the entire nail plate, causing thickening, discoloration and atrophy of the nail plate. 3. Psoriasis: If you have psoriasis, which affects the nail’s nail matrix function, the patient’s nails may become rough and have concave spots on them. Or transverse structures may appear. 4. Anemia: If there is anemia, the patient’s nails will become thin and concave in the middle while bulging around, forming a spoon-shaped nail, which can also lead to the appearance of horizontal stripes on the nails. The appearance of horizontal stripes on the cover of the thumb nail should be taken seriously, and if necessary, consult a doctor in time, complete the relevant examinations to clarify the diagnosis and carry out targeted treatment.