What Does a Lyme Disease Rash Look Like?

What does a Lyme disease rash look like? It is a question I am asked frequently in clinical practice. In this episode of the Inside Lyme Podcast, I discuss how the erythema migrans rash can appear differently depending on age, sex, duration of infection, and body location.

The study by Rebman and colleagues, entitled
“The presenting characteristics of erythema migrans vary by age, sex, duration, and body location,”
was published in Infection in March 2021.¹ The research addressed a common question: what does a Lyme disease rash look like?

The erythema migrans (EM) rash — often called the “bull’s-eye rash” — is considered a hallmark sign of Lyme disease. Many people assume it always appears as a classic circular rash with central clearing that expands beyond 2 inches.

However, Rebman and colleagues found that Lyme disease rashes vary widely in appearance. Relying only on the classic bull’s-eye pattern may lead to delayed diagnosis and treatment.

Diverse Characteristics of a Lyme Disease Rash

The authors examined 271 Lyme disease patients who presented with an erythema migrans rash to better understand what a Lyme disease rash can look like.¹

“We studied associations between these presenting characteristics [of EM rashes], as well as whether they were associated with age, sex, EM duration, body location, and initiation of antibiotics,” the authors wrote.

The patients were part of a longitudinal cohort study from three sites in Maryland and southeastern Pennsylvania. Participants were excluded if their rash measured under 5 cm (2 inches) or if symptoms had lasted longer than three months.

The study found that:

• EM rash size increased over time, peaking around 14 days.
• Males had larger rashes than females (an average of 2.8 cm larger).
• Males were more likely to have blue/red rashes.
• For every 10-year increase in age, the likelihood of central clearing decreased by 25%.
• Rashes often appeared in harder-to-see areas such as behind the thigh or behind the knee.
• Nearly 1 in 3 patients had multiple rashes.
• About one-third reported pain at the rash site.
• More than half of rashes were itchy.
• Rash shapes varied — 50.9% round, 39.1% oval, and others irregular.
• About three-quarters were red; others appeared blue/red.
• Only 28% displayed the classic bull’s-eye pattern.
• Over 90% of rashes were homogeneous rather than uneven.
• Approximately 9% presented with vesicles.

Concerns About the 5 cm Lyme Rash Cutoff

The authors raised concerns about relying on a 5 cm cutoff when identifying erythema migrans rashes.

“Applying a 5 cm size cutoff in research or surveillance settings may thus exclude a higher proportion of females with otherwise suggestive clinical histories and epidemiological risk,” the authors wrote.

The study also noted the challenge of recognizing erythema migrans in patients with darker skin tones, since 95.9% of participants identified as non-Hispanic white.

The authors suggested that differences in rash appearance between sexes and age groups may reflect variations in immune response to Borrelia infection.

Authors’ Conclusion

“Given that EM remains a clinical diagnosis, it is essential that both physicians and the general public are aware of its varied manifestations.”

Clinical Perspective

Fewer than half of Lyme disease patients develop a recognizable erythema migrans rash. This study illustrates the diversity of rash presentations among patients who do develop one.

Understanding that Lyme rashes do not always appear as the classic bull’s-eye can help clinicians recognize Lyme disease earlier and begin treatment promptly.

Questions Addressed in This Episode

• What is an erythema migrans rash?
• How often do Lyme disease patients develop a rash?
• Can Lyme disease be cultured from a rash?
• How long do erythema migrans rashes last?
• What other rashes resemble erythema migrans?
• What colors can Lyme rashes appear?
• Where are Lyme rashes most commonly located?
• What is the significance of multiple rashes?
• Can erythema migrans be itchy?
• How diverse are Lyme disease rash presentations?
• Could a rash smaller than 2 inches be important?
• How does rash appearance differ in people of color?
• Why might women present with smaller rashes?

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Thanks for listening to another Inside Lyme Podcast. You can read more about these cases in the show notes and on my website at DanielCameronMD.com.

Please remember that the advice given is general and not intended as specific medical advice. If you require individualized care, consult an experienced clinician.

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Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention