Ringworm rash (dermatophytid) is a polymorphic skin lesion that occurs at distant sites when there is significant inflammation of the foci of ringworm infection in the skin, and is a metabolic reaction of the organism to fungal metabolites. Its severity is mostly proportional to the intensity of inflammation at the foci of ringworm infection. Etiology and pathogenesis: After dermatophyte infection of the body, if the inflammation is intense, its metabolites can enter the circulation and act as antigens to stimulate the body to produce antibodies and sensitized lymphocytes, leading to the development of skin damage. Intradermal testing with ringworm can result in a tinea-like rapid-onset reaction and a tuberculin-like delayed-onset reaction; animal experiments have found that the pathological changes of ringworm rash are vascular endothelial damage and hemorrhagic inflammation, similar to those caused by heterotypic proteins. The pro-animal dermatophytes are more likely to cause ringworm rash than the relative dermatophytes. Clinical manifestations: The disease is most common in summer and autumn and often occurs during the acute inflammatory phase of various dermatophytoses, with impregnated vesicular tinea pedis and tinea pedis secondary to bacterial infection being the most common. The clinical manifestations of ringworm rash are complex, and the common types are: 1. Herpetic type: the most common. It often occurs suddenly and symmetrically on the palm and finger side. The lesions are rice-sized blisters with clear, thick walls and no surrounding redness, and in severe cases, blisters or even large blisters can appear on the palmoplantar and back of the hands and feet. Self-perceived itching and burning. As the primary infection foci subside, the blisters can dry up, flake and subside, and the lesions can recur if they do not heal. 2, eczema-like type: symmetrically distributed on the back of the feet, calves or limbs. The lesions are papules, erythema, exudation, and erosion. 3.Dermatitis-like type: distributed unilaterally or bilaterally on the lower limbs. The lesions are mildly edematous erythema, scattered in several patches or fused into a large area, similar to dermatophytosis but without significant redness, swelling and heat. In addition, ringworm rash may also present as erythema multiforme, erythema nodosum, or urticaria-like lesions. Diagnosis and differential diagnosis: ringworm rash is often confused with sweat rash, eczema, and dermatophytosis, etc. The main bases for diagnosis and differential diagnosis are: 1. It occurs when inflammation is evident in the foci of dermatophyte infection and fades as the inflammation subsides; 2. It has an acute onset and the lesions are polymorphic and often symmetrically distributed; 3. The lesions are negative for fungal examination; 4. Prevention and treatment: First of all, the primary foci of infection should be actively treated. Symptomatic treatment. Internal medications are mainly antihistamines, and local topical application of furnace glycolic lotion or glucocorticoid cream can be used.