Erythema migrans is a cutaneous eruption of a rounded shape. It is present in 80% of Lyme disease cases, a disease caused by a tick bite. This symptom is thus a good indicator of the disease, even if it is not a diagnosis by itself. The red spot, often warm, progressively expands around the bitten area, forming a ring that can reach up to ten centimeters in diameter. Erythema migrans does not cause itching or pain, despite its impressive appearance.