Erythema migrans (EM) or "bull's-eye" rash medical illustration of Erythema migrans Rash occurs in approximately 70-80% of infected persons1 and begins at the site of a tick bite after a delay of 3-30 days (average is about 7 days). Rash gradually expands over a period of several days, and can reach up to 12 inches (30 cm) across. Parts of the rash may clear as it enlarges, resulting in a “bull's-eye” appearance. Rash usually feels warm to the touch but is rarely itchy or painful. EM lesions may appear on any area of the body.