Erythema Migrans

Erythema migrans is a distinctive expanding rash that appears in over 70 percent of people with Lyme disease, serving as the most recognizable early warning sign of this tick-borne infection.

Table of contents

• What is Erythema Migrans?
• How the Rash Looks
• When the Rash Appears
• Associated Symptoms
• Diagnosis and Medical Care
• Treatment
• Prevention

What is Erythema Migrans?

Erythema migrans is a circular, expanding rash that often appears in the early stages of Lyme disease. The name comes from Latin words meaning “migrating redness.” This rash is not an allergic reaction to a tick bite, but rather an actual skin infection caused by bacteria called Borrelia burgdorferi^[1].

The rash is so distinctive that it allows doctors to diagnose Lyme disease without laboratory tests in many cases. Erythema migrans is the only manifestation of Lyme disease in the United States that is sufficiently characteristic to permit clinical diagnosis without laboratory confirmation^[2].

Approximately 70 to 80 percent of people with Lyme disease will develop this rash^[1][4]. However, this also means that about 20 to 30 percent of infected people never develop the rash at all, which can make diagnosis more challenging.

How the Rash Looks

While many people think of erythema migrans as a “bull’s-eye” rash, this appearance is actually less common than most believe, especially in the United States. In Europe, about 79 percent of cases show the bull’s-eye pattern, but in the United States, only about 19 to 20 percent of cases develop this distinctive look^[2][3].

The typical erythema migrans rash in the United States is usually a solid, blanching, red patch rather than a bull’s-eye appearance^[3]. The rash is usually circular or oval, and may be red or bluish in color^[2]. It often appears uniformly red without a clear center^[6].

The most distinctive features of erythema migrans are the speed and extent to which it expands. The rash typically grows 2 to 3 centimeters per day and can reach a diameter of 5 to 70 centimeters, with 50 percent of cases reaching more than 16 centimeters^[2]. In simpler terms, the rash usually measures about 2 to 2.5 inches when first noticed and can expand to 12 inches or more^[4].

The rash typically appears at the site of the tick bite, often in areas where ticks commonly attach, such as near skin folds like the armpit, groin, or back of the knee. In children, the rash may appear in the hair, ear, or neck area^[2]. The rash may feel warm to the touch but is usually not itchy and is rarely tender or painful^[2][4].

In some cases, multiple rashes can appear on different parts of the body. These additional rashes are not caused by multiple tick bites but occur as a reaction when the bacteria moves through the body^[5].

The rash is not transmitted from person to person^[5]. It can be harder to see on darkly pigmented skin, which may lead to delayed diagnosis^[6].

When the Rash Appears

The erythema migrans rash appears anywhere from one day to one month after a tick bite, though most commonly it shows up within 3 to 30 days^[2][4]. For most people, the rash will appear within 7 to 10 days after being bitten^[4].

The initial sign is usually a reddened area near the tick bite. As the rash increases in size over several days or weeks, it may sometimes clear in the middle and develop a red ring around the outside, creating the bull’s-eye pattern^[5].

It is important to understand that many people notice a bump or redness immediately after a tick bite, but this usually goes away in a few days and is not a sign of Lyme disease^[4]. The localized reaction to a recent tick bite differs from erythema migrans in size, appearance, and duration^[3].

If left untreated, the rash takes up to four weeks to resolve on its own^[2]. However, even if the rash disappears, the infection remains in the body and can progress to more serious stages if not treated with antibiotics.

Associated Symptoms

The erythema migrans rash is often accompanied by symptoms that resemble a viral illness. These symptoms may include fatigue, headache, body aches, fever, chills, muscle and joint pain, and swollen lymph nodes^[2][6]. However, Lyme disease is not typically associated with cold-like symptoms such as a runny nose, prominent cough, or prominent diarrhea^[6].

Some people may have the rash but feel no other symptoms, making it easy to miss the significance of the rash. In other cases, these flu-like symptoms may appear without a rash, or may linger after the rash disappears^[2].

Most people who get infected do not remember seeing a tick or being bitten^[2]. This is because the ticks that transmit Lyme disease can be very small, especially in their nymph stage when they are about the size of a poppy seed^[15].

Diagnosis and Medical Care

If you notice a rash and think you may have been bitten by a tick, you should contact a doctor as soon as possible^[4]. A diagnosis of Lyme disease can be made if you have an erythema migrans rash and have recently been bitten by a tick, or if you were in an area where a tick bite was likely^[4].

Because Lyme disease can cause long-term complications within a few weeks if left untreated, anyone with a rash and a recent history of outdoor activities in areas where Lyme disease is common should seek medical attention for diagnosis^[2].

Routine testing for Lyme disease is not recommended unless a person has a known or plausible exposure and presents with the characteristic rash^[12]. In fact, when erythema migrans is present along with a history of potential tick exposure in an area where Lyme disease is common, a clinical diagnosis can be made without laboratory confirmation^[13].

Many patients with Lyme disease have delayed seeking treatment because their rash did not have the classic bull’s-eye appearance they expected^[3]. It is important to know that most erythema migrans rashes do not look like a bull’s-eye, especially in the United States.

Treatment

People treated with appropriate antibiotics in the early stages of Lyme disease, when erythema migrans appears, usually recover rapidly and completely^[8][10]. Early diagnosis and proper antibiotic treatment can help prevent more severe, late-stage Lyme disease^[8].

For adults, the recommended antibiotics include doxycycline (100 mg twice daily for 10 to 14 days), amoxicillin (500 mg three times daily for 14 days), or cefuroxime (500 mg twice daily for 14 days)^[8][14].

For children, doxycycline (4.4 mg per kilogram of body weight per day divided into two doses, not exceeding 100 mg per dose, for 10 to 14 days), amoxicillin (50 mg per kilogram per day divided into three doses, not exceeding 500 mg per dose, for 14 days), or cefuroxime (30 mg per kilogram per day divided into two doses, not exceeding 500 mg per dose, for 14 days) are recommended^[8][14].

For people who cannot take doxycycline or the medications in the penicillin family, azithromycin may be used, although it is less effective. People treated with azithromycin should be closely monitored to ensure that symptoms resolve^[8][14].

When different durations of antibiotics are shown to be effective, the shorter duration is preferred to minimize side effects, including infectious diarrhea and antimicrobial resistance^[8][14]. Most cases of Lyme disease can be treated with 10 to 14 days of antibiotics^[10].

Prevention

Preventing tick bites is the most effective way to avoid erythema migrans and Lyme disease. Several protective measures can reduce your risk^[12][13]:

• Use insect repellents that contain 20 to 30 percent DEET on exposed skin and clothing. Other effective ingredients include picaridin, IR3535, oil of lemon eucalyptus, PMD, 2-undecanone, or permethrin^[12][13].
• Wear protective clothing including long sleeves, long pants tucked into boots or socks, and light-colored clothing that makes it easier to spot ticks^[12][15].
• Avoid tick habitats by staying on marked trails and avoiding tall grasses, weeds, and brush where ticks climb and wait for hosts^[12][15].
• Perform thorough tick checks after being outdoors. Check your entire body, paying close attention to areas like the armpits, groin, scalp, behind the knees, in between toes, in the navel, along clothing lines, in or behind the ears, and in skin folds^[12][15].
• Shower within two hours of outdoor activity to help remove ticks that haven’t attached yet^[15].

If you find a tick attached to your body, remove it as quickly as possible. Prompt detection and removal of an attached tick can reduce the likelihood of disease transmission^[12][13]. While it is important to remove a tick quickly, removing it within the first 24 hours can prevent transmission of most tick-transmitted diseases^[15]. In general, infected ticks must be attached for more than 24 hours to spread the infection^[2].

To remove a tick properly, use fine-tipped tweezers. Grasp the tick close to the skin and pull upward with steady, even pressure. Avoid twisting or yanking, as this can result in part of the tick’s mouth remaining attached^[12][13][15]. Clean the bite area and your hands with alcohol or soap and water after removal.

In certain circumstances, a single dose of doxycycline within 72 hours of tick removal may be given as preventive treatment after a high-risk tick bite. A bite is considered high risk if it is from a blacklegged tick in a highly endemic area and the tick was engorged and attached for 36 hours or more^[9][10][12]. However, in general, the CDC does not recommend antibiotics after all tick bites^[10]. Ask your healthcare provider if preventive antibiotics are appropriate for you.