A red rash around a tick bite is indicative of a tick-borne disease, such as southern tick associated rash illness (STARI) or Lyme disease, according to the Centers for Disease Control and Prevention. As the rash expands, it can reach up to 12 inches in diameter.
Both tick-borne diseases frequently appear as red rashes in a bull's eye pattern, with centralized redness at the site of the bite, followed by a circumference of clear skin, and then another thin circle of redness, explains the CDC. The rash in Lyme disease cases typically appears three to 30 days after the initial bite, and fever and fatigue often accompany it. The rashes are commonly warm to the touch as well.