Introducing AcuDart

Partnering with industry leading laboratories to create the most accurate tick-borne disease testing from the comfort of home.

What is Erythema Migrans (EM)?

back to glossary >>

Erythema Migrans (EM) is a characteristic skin rash that appears in the early stage of Lyme disease. It is one of the first clinical signs of infection with Borrelia burgdorferi, the bacterium responsible for Lyme disease, and occurs at the site of a tick bite.

The rash typically develops 3 to 30 days after a bite and gradually expands outward, often resembling a bull’s-eye pattern with a red center, a clearing, and an outer red ring.

While an EM rash is strongly indicative of Lyme disease, not all Lyme patients develop or notice a rash. Studies suggest that 20–30% of infected individuals never develop EM, making laboratory testing for Lyme disease essential, especially if symptoms persist.

What Does an Erythema Migrans Rash Look Like?

EM rashes vary in size, shape, and color but commonly share these features:

Expanding red or pink circular rash (often >5 cm in diameter)
May resemble a bull’s-eye (red center, pale middle ring, red outer edge)
Warm to the touch but usually not painful or itchy
Gradually enlarges over days to weeks
May appear anywhere on the body, often at the site of a tick bite (legs, groin, armpits, torso, back of the knee, or scalp)
Multiple EM rashes can occur if the infection spreads through the bloodstream

Since not all EM rashes look like the classic bull’s-eye, any expanding red rash after a tick bite should be evaluated by a doctor.

Erythema Migrans vs. Other Skin Rashes

EM can be mistaken for:

Spider bites (which usually don’t expand over time)
Ringworm (Tinea) (a fungal infection with a raised scaly edge)
Allergic reactions (which are itchy and do not gradually spread)

A history of a tick bite and the rash’s slow expansion are key clues that it is Lyme-related.

What to Do If You Have an EM Rash?

Seek medical attention immediately—an EM rash may mean you have Lyme disease and require treatment.
Early antibiotic treatment (e.g., doxycycline, amoxicillin, or cefuroxime) can prevent Lyme from spreading to the joints, nervous system, and heart.
Monitor for additional symptoms such as fever, fatigue, headaches, and joint pain, which may indicate the infection is spreading.

Key Takeaways

Erythema Migrans (EM) is an early sign of Lyme disease, appearing as an expanding red rash.
A classic bull’s-eye pattern is common but not always present—some EM rashes are uniform red or blotchy.
Early antibiotic treatment is crucial to prevent Lyme disease from progressing.
If no rash is present but Lyme symptoms occur, laboratory testing should be done.

For accurate Lyme disease and co-infection testing, visit AcuDart Health.

Shop All Tick-Borne Disease Tests

Front of Package for AcuDart Tick-Borne Disease At-Home Screening Test Panel

Back of Package for AcuDart At-Home Screening Tests

Package Contents of AcuDart At-Home Screening Tests

AcuDart Tick-Borne Disease Screening Test Panel

Sample AcuDart Tick-Borne Disease At-Home Screening Test Panel Results Report

AcuDart Tick-Borne Disease Screening Test Panel

$499.00

$596.00

Tick-borne diseases like Lyme disease, Tick-Borne Relapsing Fever (TBRF), Babesiosis, and Bartonellosis share overlapping symptoms, making diagnosis difficult without comprehensive testing. Because these infections can mimic each other, relying on a single test for one disease may lead to missed or delayed diagnoses. That’s why AcuDart offers the most accurate and reliable tick-borne disease testing available.

Unlike standard tests from commercial labs like LabCorp or Quest, which typically screen for just one or two species per disease, the AcuDart Tick-Borne Disease Test Panel is designed for maximum accuracy and coverage. It detects 19 species across four major tick-borne diseases, making it the most comprehensive tick panel on the market. Whether you're experiencing persistent symptoms or have been exposed to ticks, AcuDart's tick-borne disease panel provides the most thorough and precise testing to help you get the right diagnosis and treatment faster.

Quantity