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What to Know About Erythema Migrans

Medically Reviewed by Dan Brennan, MD on April 14, 2021

Erythema migrans is a rash that frequently appears as one of the first symptoms of Lyme disease. It's typically a circular red area that sometimes clears in the middle, forming a bull's-eye pattern. It can spread up to 12 inches across and may be warm to the touch. It's not usually itchy or painful and may appear in more than one place on the body.

Approximately 70% to 80% of people with Lyme disease, which is spread by ticks, will develop erythema migrans. It will usually show up at the site of a tick bite within 3 to 30 days after being bitten. It will gradually expand, although it doesn't always appear the same on everyone.  

What Causes Erythema Migrans?

Erythema Migrans is often the first sign of Lyme disease. Lyme disease is caused by the bacteria Borrelia burgdorferi. The bacteria are transmitted to humans through infected deer ticks. Dog ticks and wood ticks don't transmit Lyme disease. The Centers for Disease Control and Prevention (CDC) estimates that there are 300,000 cases of Lyme disease each year, though the actual number reported is much lower.  

What Are the Symptoms of Erythema Migrans?

The first sign of erythema migrans is redness at the site of a tick bite. It will start to expand into a round or oval red skin lesion. The most common manifestation of erythema migrans is a uniformly round or oval rash that expands to more than 2 inches in diameter. Sometimes the inside of the lesion clears, leaving a bull's-eye type pattern. 

Because erythema migrans is an early symptom of Lyme disease, you may also have additional symptoms of Lyme disease, including:

Using Erythema Migrans to Diagnose Lyme Disease

Many cases of Lyme disease are initially misdiagnosed. The early symptoms of Lyme disease are common symptoms that occur with many illnesses.  Although not all people with Lyme disease have erythema migrans, recognizing it when it is present is an important part of early diagnosis and treatment.  

When erythema migrans is present, it can be the basis of a diagnosis by itself since early blood tests are not always reliable. You should understand that the bullseye pattern is only present in a minority of cases. Most often, the lesion is a solid red or blue-red oval or circle. The lesion expands over several days and may have blisters in the center, though this is not common. 

If no rash is present or it goes unnoticed, and you don't remember being bitten by a tick, it can be difficult to diagnose Lyme disease. Testing early in the disease process will likely show a false negative, as your body hasn't had time to develop a response that can be measured. Once your body does develop a response, you may get a positive test for years, even after Lyme disease has been properly treated.

How Is Erythema Migrans Treated?

Because Lyme disease is caused by bacteria, it's treated with antibiotics. The sooner you start antibiotics, the quicker and more complete your recovery will be. 

Oral antibiotics. Early-stage Lyme disease is treated with oral antibiotics. Doxycycline is usually used to treat Lyme disease in adults and children over the age of 8.   Amoxicillin or cefuroxime is usually used for younger children and pregnant or breastfeeding women. Oral antibiotics are usually given for 14 to 21 days, although a 10-to-14-day course may be just as effective. 

Intravenous (IV) antibiotics. If Lyme disease involves your central nervous system, you may need IV antibiotics for 14 to 28 days. This will eliminate the infection, but it may take awhile for you to completely recover from your symptoms.   

How to Prevent Lyme Disease

The deer ticks that carry the bacteria that transmit Lyme disease are most prevalent in New England, the mid-Atlantic states, and the upper Midwest of the United States. They live in moist and woody environments. If you're going to be in an area like this, use an insect repellent that contains DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol, or 2-undecanone. You should also:

  • Check your body for ticks after being outside. 
  • Check your clothing and pets for ticks. 
  • Place clothes in a dryer on high heat to kill ticks.
  • Remove attached ticks with tweezers as soon as you notice them. 
  • Watch for symptoms of Lyme disease after you remove a tick. 
  • Contact your healthcare provider if you develop a fever or rash, even if you don't remember being bitten. 
  • Treat your animals using veterinarian-prescribed tick prevention products to keep them from bringing ticks into your house. 
  • Discourage deer from coming into your yard by removing plants that attract them and putting up fences. 
  • Create a tick-safe zone in your yard by using chemical control agents and keeping the area clean of yard debris. 
WebMD Medical Reference

Sources

SOURCES:

Centers for Disease Control and Prevention: "Prevent Lyme Disease," "Signs and Symptoms of Untreated Lyme Disease."

Cleveland Clinic: "Lyme Disease."

Johns Hopkins Lyme Disease Research Center: "Lyme Disease Signs & Symptoms."

Mayo Clinic: "Lyme disease."

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