According to the CDC, a bull's-eye rash is a common symptom of Lyme disease. The CDC states that as many as 80 percent of individuals affected by Lyme disease develop this easy-to-spot red rash as early as three days after being bitten by a tick.
A bull's-eye rash is a flat, painless rash that is officially referred to as an erythema migrans by health care professionals. The rash may accompany other symptoms, such as joint pain or swollen lymph nodes. Left untreated, the disease can spread to other parts of the body and damage muscles, joints and the spinal cord, warns the CDC.