Erythema behind the ear is common in young women, and the disease is common in the spring and autumn, and usually patients have a rash that occurs symmetrically on the lower legs. The rash is a number of nodules of varying sizes, bright red, dark red, and other colors. The patient may feel painful. So how to check for erythema behind the ear? Let me introduce this disease in detail and let’s analyze some issues related to this disease. Viral particles can be seen by electron microscopy in the acute phase, and specific IgM antibodies in the serum are detected in the acute phase or early recovery. Specific viral DNA can be detected in serum and throat secretions. 1.Blood test Peripheral blood leukocytes can be mildly reduced or normal, and hemoglobin and platelets can be reduced in those with remitting crisis. 2.B19 DNA test PCR method can detect DNA from patient’s serum, CSF and lesion tissue, which is a means to confirm the diagnosis. 3.Immunological examination B19 antigen in serum can be detected by radioimmunoassay or ELISA method, and IgM antibody of B19 is more frequently used, which can reach the peak in 1 week of disease and decline after 2 months, so it has the diagnostic value of presenting infection. Pathological changes Epidermal cells are edematous, dermal papillae are vasodilated, endothelial cells are swollen, and there is histiocytic infiltration around blood vessels, hair follicles and sweat glands, but they are chronic inflammatory changes and have no diagnostic value.