Erythema migrans (EM) or "bull's-eye" rash

• Rash occurs in approximately 70 to 80 percent of infected persons and begins at the site of a tick bite after a delay of 3 to 30 days (average is about 7 days).
  
  NOTICE: 70 to 80% ≠ 100% (keep that on your mind because neuroborreliosis can destroy your life!).
• 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 rash may appear on any area of the body.

Early disseminated stage of Lyme disease

Untreated, the infection may spread from the site of the bite to other parts of the body, producing an array of specific symptoms that may come and go.

For more information please visit CDC's site.