Lichen planus, commonly known as sweat spots, is caused by a fungus, the fungus Sphaerococcus furfur. This fungus, however, is a common putrefactive parasite on normal human skin and can only make a person sick in some special cases. Its name is sweat spot, which is seen to be related to sweating a lot. It is more common in tropical and subtropical areas because sweat and dust and dander form dirt and decay to provide conditions for the lichen planus bacteria to grow and multiply. Young people, especially young men, sweat a lot because they are active, and if they don’t change their clothes and wipe their skin dry in time, it is easy to develop lichen planus. It is also common in people who apply corticosteroids, because the epidermal cell replacement cycle of these people is prolonged, which is conducive to the growth of fungi, and if the hormone is discontinued, lichen planus will improve. In addition, weakness, malnutrition, diabetes and pregnancy can trigger the disease. Lichen planus occurs in sweaty areas such as the chest, abdomen, upper arms, back and neck, and sometimes the face. The rash begins as tiny spots, mostly around the hair follicle opening, and then gradually expands to form patches of varying size and color, ranging from pale white to dark brown, on which tiny bran-like scales are visible. The lesions develop over time and may form depigmented patches that do not fade easily over time. There is rarely an inflammatory reaction in lichen planus because the fungus only lives in the stratum corneum of the skin. Occasionally, itchiness may be present when the lesions are active. Treatment may include salicylic acid and benzoic acid preparations, 10% clotrimazole cream and tinctures. Because ringworm can survive on the skin and clothing and bedding, it often recurs, so to treat it thoroughly, you need to clean and disinfect your clothing and bedding. The easiest way to do this is to wash them and expose them to sunlight. Treatment is due to the special nature of the residual pigment of lichen planus, so it is important to explain it well to the patient to avoid misunderstanding.