Erythema migrans

This page offers information about the red rash erythema (chronicum) migrans, which can develop after a tick bite, and which is characteristic of Lyme disease. This erythema migrans mark is popularly also called tick bite, but on this site that term is used for referring to the bite of a tick.

What is an erythema migrans?

In case of an infection with the Lyme-bacterium Borrelia burgdorferi (Bb), a typical skin condition known as erythema migrans (EM) can develop at the location of the tick bite days to weeks after the tick bite.

When does an erythema migrans develop?

Only in case of an infection with Borrelia burgdorferi, but note that not everyone that gets infected with Bb develops an erythema migrans, while an infected person may develop other symptoms later anyway.

How does an erythema migrans look like?

Typically a red rash develops, that expands gradually and often clears in the center, so that a ring is formed. This is also called a bulls eye rash. But it doesn't always look the same: there may form multiple rings around one tick bite spot, there may not really form a ring, but just a red expanding rash, and the color may be more bluish-red. On dark skin it will also look different.

Do not confuse it with a small red spot that looks like a mosquito bite, which is just an irritation of the skin caused by the tick bite.

Photos of the erythema migrans

erythema migrans on leg of boyerythema migrans on shoulder

Pictures of the tick bite rash erythema migrans on the thigh of a child (upper left image), and an EM rash on the shoulder (upper right image).

Erythema migrans rasherythema chronicum migrans

Pictures of the Lyme disease bullseye rash erythema migrans.

Where does an erythema migrans develop?

Normally at the location of he tick bite, but it can also develop at other sites, and sometimes there can be multiple at the same time, when the bacterium has disseminated (spread) throughout the body. An erythema migrans can also reappear.

How quickly does an erythema migrans arise?

Usually within a a few days to several weeks, but sometimes even after months.

How is an erythema migrans diagnosed?

If a typical erythema migrans occurs after a tick bite, then no further examination like blood tests is necessary. However, an erythema migrans can also resemble other skin conditions. So, if no tick bite has been noticed and there is doubt about the diagnosis, then Lyme disease (Borrelia antibody) blood tests can be done. It is also possible to investigate the affected skin itself via a biopsy.

How is an erythema migrans treated?

In national treatment guidelines typically a treatment of at most 14 days with antibiotics is advised.However, some doctors advise (and treat with) 6 weeks of higher dosed antibiotic treatment in case of an erythema migrans.

Document the erythema migrans!

Take a picture of the (suspected) erythema migrans and note the date of taking the picture; circle the erythema migrans with a ballpoint pen and take another picture a few days later, so that the enlargement of the rash can be shown. It would be best to take a photo (or photos) every day, so that the progress of the rash can be seen. Also keep notes of possible other symptoms and data that may be relevant.

Many people are bitten by a tick unnoticed and only a portion of the people who become infected will get an erythema migrans. The erythema migrans is sometimes also difficult to see, because it is very light, or because it is hidden from the eye (like under the hair or on the back).

At the time of the appearance of an erythema migrans antibiotics should be taken immediately, without waiting for results of tests. No time should be wasted unnecessarily: the longer one is infected, the harder it is to cure.