Erythema Migrans
What is Erythema Migrans?
Erythema migrans is a distinctive expanding rash that appears after a tick bite. It is the most common and recognizable sign of early Lyme disease. The rash typically starts as a small red spot at the bite site and gradually expands outward over days to weeks.
The classic appearance is a bull's eye pattern with a clear center and red outer ring. However, not all cases look this way. Some rashes are uniformly red or have multiple rings. The rash usually appears 3 to 30 days after a tick bite, with an average of 7 days. It is not painful or itchy in most cases.
Erythema migrans is caused by bacteria called Borrelia burgdorferi, which are transmitted through blacklegged tick bites. Catching and treating the infection early prevents serious complications. Without treatment, the bacteria can spread to joints, the heart, and the nervous system.
Symptoms
- Expanding red rash at the site of a tick bite
- Bull's eye pattern with clear center and red outer ring
- Rash that grows larger over days, often reaching 6 inches or more across
- Warm skin at the rash site, but usually not painful or itchy
- Fatigue and general feeling of being unwell
- Fever and chills
- Headache
- Muscle and joint aches
- Swollen lymph nodes
Some people with Lyme disease never notice a rash. Others may have a tick bite in a location that is hard to see. Early symptoms can be mild and easy to miss.
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Causes and risk factors
Erythema migrans is caused by infection with Borrelia burgdorferi bacteria. These bacteria live in blacklegged ticks, also called deer ticks. When an infected tick bites and stays attached for 36 to 48 hours or longer, it can transmit the bacteria into your bloodstream. The rash develops as your immune system responds to the spreading infection.
Risk factors include spending time in wooded or grassy areas where ticks live, especially in the Northeast, Mid-Atlantic, and upper Midwest regions. Activities like hiking, camping, gardening, and hunting increase exposure. Not using tick repellent or protective clothing raises your risk. Ticks are most active from April through September, making spring and summer the highest risk seasons.
How it's diagnosed
Doctors usually diagnose erythema migrans based on the appearance of the rash and a history of possible tick exposure. The distinctive expanding pattern is often enough for diagnosis. If you have the characteristic rash, treatment typically starts right away without waiting for test results.
Blood testing for Lyme disease antibodies can confirm the diagnosis, but early tests may be negative. Your immune system takes 3 to 4 weeks to produce IgM antibodies after the rash appears. IgG antibodies develop later. Rite Aid offers Lyme Disease Antibody testing as an add-on to help monitor your antibody response and confirm infection when clinical diagnosis needs support.
Treatment options
- Oral antibiotics are the primary treatment, typically doxycycline for 10 to 21 days
- Amoxicillin or cefuroxime are alternative antibiotics for those who cannot take doxycycline
- Starting treatment early prevents the infection from spreading to other body systems
- Remove ticks promptly using fine-tipped tweezers to reduce infection risk
- Wear long sleeves and pants when hiking or in wooded areas
- Use EPA-registered insect repellents containing DEET or picaridin on skin and clothing
- Check your body for ticks after outdoor activities, especially in hair and skin folds
- Shower within 2 hours of coming indoors to wash off unattached ticks
- Create tick-safe zones in your yard by removing leaf litter and keeping grass mowed
- See a doctor immediately if you develop a rash after a tick bite
Need testing for Erythema Migrans? Add it to your panel.
- Simple blood draw at your nearest lab
- Results in days, not weeks
- Share results with your doctor
Frequently asked questions
The rash typically lasts 3 to 4 weeks if left untreated. It may fade on its own even without antibiotics. However, the absence of the rash does not mean the infection is gone. Without treatment, the bacteria remain in your body and can cause serious complications weeks to months later.
Yes, about 20 to 30 percent of people with Lyme disease never develop the characteristic rash. Some may not notice a rash in hard-to-see areas. Others may experience only flu-like symptoms. This is why awareness of tick exposure and other symptoms is important for early diagnosis.
If you develop a rash, see a doctor right away for clinical diagnosis. Blood testing is most accurate 4 to 6 weeks after initial infection when antibodies have developed. Testing too early can produce false negative results. Your doctor may recommend testing if symptoms persist or if diagnosis is uncertain.
No, only about 50 to 70 percent of cases have the classic bull's eye appearance. Many rashes are uniformly red without a clear center. Some have irregular shapes or multiple rings. Any expanding red rash after a tick bite should be evaluated by a doctor, regardless of its exact appearance.
The rash typically expands at a rate of about 1 inch per day. It often reaches 6 to 8 inches in diameter but can grow much larger. Some rashes expand to 12 inches or more. The expansion happens gradually over several days to weeks.
Yes, as the bacteria spread through your bloodstream, multiple rashes can appear in different locations. These secondary rashes are usually smaller than the original. They indicate that the infection is disseminating and requires prompt antibiotic treatment to prevent further complications.
No, you cannot catch erythema migrans or Lyme disease from another person. The infection only spreads through tick bites. Even if someone in your household has Lyme disease, you are not at risk unless you are also exposed to infected ticks in the same environment.
Untreated Lyme disease can spread to joints, causing arthritis, especially in the knees. It can affect the heart, causing irregular heartbeat or chest pain. The bacteria can also invade the nervous system, leading to facial paralysis, numbness, or memory problems. Early treatment with antibiotics prevents these serious complications.
Antibiotic treatment is highly effective when started early. Most people recover fully after a 10 to 21 day course of oral antibiotics. The rash typically fades within a few days of starting treatment. Early treatment prevents nearly all cases of late-stage Lyme disease complications.
The original rash should not return after successful treatment. However, you can get Lyme disease again if bitten by another infected tick. Having Lyme disease once does not provide lasting immunity. Continue using tick prevention measures even after recovery to avoid reinfection.