Pityriasis vulgaris, formerly known as lichen planus and commonly known as sweat spot, is a superficial fungal disease caused by Malassezia infection of the epidermal stratum corneum. The disease is chronic, with mild inflammation, and usually without conscious symptoms. The damage is characterized by scattered or fused hypopigmented or hyperpigmented spots with furfuraceous desquamation on the chest, back, upper arms, axillae, and sometimes the face. Lichen planus, commonly known as sweat spots, is caused by the bacterium Stachybotrys furfur. It is caused by the bacterium Malassezia furfur. It is common in summer when the skin is sweaty and humid. It is most common in adults and occurs on the chest, back, neck, and upper arms. At first, it is a round spot the size of a soybean, grayish white, brown or yellowish, with small bran-like scales attached to it, and later the rash becomes more and more numerous and can fuse into a sheet. After removal of the scales, temporary hypopigmented patches are left behind, often without conscious symptoms or with a slight itch. Typical lichen planus can be determined at a glance by an experienced physician and requires laboratory tests to confirm the diagnosis, while atypical cases need to be differentiated from other pigmentary abnormalities of the skin. Treatment of lichen planus is relatively simple. Itraconazole is given orally once a day at 200 mg with or without a meal for one week. Topical preparations, 3% Celebrex lotion to wash the affected area 1-2 times a day, and topical application of Vucozine cream, clotrimazole cream, butenafine ointment, and econazole drops are effective; 2.5% selenium sulfide solution can also be used topically; or topical application of 20%-30% sodium thiosulfate solution. Sometimes lichen planus can recur, but don’t be afraid, it doesn’t affect your health except for the unattractive appearance.