Lyme disease has long been associated with the appearance of a circular rash radiating out from the site of an infected tick bite, known as an erythema migrans (EM) rash. Erythema migrans can take many forms. The best-known EM rash is the so-called “bull’s-eye” or target rash, which consists of concentric circles of redness around a central clearing. Unfortunately, not all patients notice this or any kind of rash due to the following:

• Ticks often bite the scalp, behind the ears, in the middle of the back, or other places that are hard for a patient to inspect.
• The EM rash may appear as a dark bruise on dark skin and often goes unnoticed.
• Not all EM rashes look like the classic “bull’s-eye” rash. Many other variations are now being reported, with the most common being a skin lesion that is uniformly red without the rings or target appearance.

Some scientists believe that certain strains of Lyme do not produce a rash at all. In fact, Harvard Medical School’s Dr. Jonathan Edlow reported as early as 2002 that the target or “bull’s-eye” is no longer considered the most common type of rash associated with Lyme disease.

EM rashes can be uniform in color, oozing, blistered, scaly, and in a variety of shapes. They can range from a pink color to shades of deep red, purple, or brown. Generally, neither itching nor pain is present, but occasionally an EM rash can be warm to the touch, burning, itching, or painful. Although lesions are defined, for surveillance purposes, as being greater than 5cm in size, smaller lesions that are culture-positive for B burgdorferi have been reported. Some doctors think that multiple rashes appearing on different parts of the body are a sign of rapidly-spreading infection. Frequent misdiagnoses include ringworm, cellulitis and spider bites.

Learn more from visual examples:
http://phpa.dhmh.maryland.gov/OIDEOR/CZVBD/Shared%20Documents/Lyme_MD_poster_FINAL.pdf

According to the Centers for Disease Control, the EM rash is noticed in 70 to 80 percent of persons who contract Lyme disease. However, other studies have suggested that this percentage may be as low as 50 percent or less. EM rashes may appear in a few days or several weeks after the bite and may recur with antibiotic treatment.

Co-infections of Lyme can also cause rashes. Rocky Mountain Spotted Fever is well-known for the spotted rash it produces on the hands and feet, along with fever and virus-like symptoms. RMSF can be fatal if treatment is not given promptly. Bartonella or cat-scratch fever can cause pink or purple streaks in the skin, which resemble stretch marks. Finally, tularemia can cause ulcerated sores at the site of the tick bite. Other dermatological manifestations of these infections are possible.

Although not every tick-borne infection causes rashes, many do. Therefore, patients should seek immediate medical care if any kind of rash appears anywhere on the body after exposure to ticks.