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. There are some difficulties with this. First, scientists believe that some strains of Lyme do not produce a rash at all. Second, 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. Finally, not all EM rashes look like the classic “bull’s-eye” rash since many other variations are now being reported.
In fact, Harvard Medical School professor Dr. Jonathan Edlow reported in 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. Occasionally an EM rash is warm to the touch or burning, itching, or painful. A so-called mini-EM rash with a diameter of 5 cm or less has been reported in Europe. Some doctors think that multiple rashes appearing on different parts of the body is a sign of rapidly-spreading infection.
The EM rash may also appear as a dark bruise. Frequent misdiagnoses include ringworm, cellulitis, and spider bites. 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. ILADS reports that fewer than 50% of people with Lyme disease recall the rash. 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 famous 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 disease can cause pink or purple streaks in the skin which resemble stretch marks. Other dermatological manifestations of these infections are possible.
Although not every tick-borne infection causes rashes, an EM rash means you have Lyme disease. Therefore, seek immediate medical care if any kind of rash appears anywhere on the body after exposure to ticks. This way your doctor can take a look at it, and put you on antibiotics immediately before the disease moves into the more chronic stage.
Taken from NatCap