Borrelia burgdorferi is a spiral-shaped bacterium that causes Lyme disease, transmitted to humans through the bite of infected black-legged ticks. The infection begins when a tick, often an unnoticed nymph, attaches to the skin and begins its feeding process. During this time, the bacteria migrate from the tick’s salivary glands into the human host. As the bacteria multiply and spread outward from the bite, they trigger an inflammatory response that leads to characteristic skin manifestations.
Erythema Migrans: The Primary Skin Lesion
The most common sign of an early Borrelia burgdorferi infection is a rash known as Erythema Migrans (EM). This skin lesion appears at the site of the tick bite 3 to 30 days after the encounter. Caused by the outward migration of the spirochetes through the skin, the rash begins as a small red spot that gradually expands over days or weeks.
A defining characteristic of Erythema Migrans is its size; the rash must expand to at least 5 centimeters in diameter to be clinically significant. While known for its “bull’s-eye” appearance, this pattern occurs in less than half of cases. Many rashes are uniformly red or bluish-red and oval-shaped, without central clearing. The lesion is not painful or itchy, though some individuals may experience a mild burning sensation.
The rash can be accompanied by flu-like symptoms, including fever, headache, and fatigue, which indicates the bacteria are spreading through the body. Although EM can appear anywhere, common locations include the thigh, groin, and armpit. In children, these rashes are more frequently seen on the head and neck.
Later-Stage and Atypical Skin Manifestations
If an early infection is not addressed, the bacteria can disseminate, leading to distinct skin conditions months to years later. One rare manifestation is Borrelial lymphocytoma, which presents as a solitary, bluish-red nodule or plaque. This lesion is a dense accumulation of immune cells and appears on the earlobe in children or the nipple area in adults.
Another later-stage skin condition, more common with European strains of the bacteria, is Acrodermatitis chronica atrophicans (ACA). This condition develops progressively, beginning six months to several years after the initial infection. ACA affects the hands and feet, starting with an inflammatory phase of bluish-red discoloration and swelling of the skin.
Over time, this inflammatory stage gives way to a chronic, atrophic phase where the skin becomes thin, wrinkled, and fragile, with a “cigarette-paper” texture. The underlying veins may become more visible, and fibrous nodules can develop near the joints. This progression results from the long-term presence of Borrelia in the skin tissue.
Diagnosis Through Skin Examination
The diagnosis of Lyme disease often relies on a skin examination. In regions where Lyme disease is prevalent, the appearance of a characteristic Erythema Migrans rash is sufficient for a physician to make a clinical diagnosis. This allows for prompt treatment without waiting for laboratory confirmation.
This reliance on clinical signs exists because blood tests that detect antibodies can be unreliable early in the infection. The antibodies to Borrelia burgdorferi can take several weeks to develop to a detectable level. Therefore, a blood test performed while the EM rash is present may produce a false-negative result.
The visual identification of the expanding rash is the most reliable indicator for early Lyme disease. A physician will consider the rash’s appearance, its expansion over time, and the patient’s history of potential tick exposure. This approach ensures that treatment is not delayed, which is important for preventing later-stage complications.
Treatment and Skin Symptom Resolution
Once Lyme disease is diagnosed from skin manifestations, the standard treatment is a course of oral antibiotics, such as doxycycline or amoxicillin. The specific antibiotic chosen depends on the patient’s age and medical history. For early Lyme disease with an Erythema Migrans rash, a treatment duration of 10 to 21 days is standard.
Following the start of antibiotic therapy, skin symptoms resolve quickly. The Erythema Migrans rash starts to fade within a few days of starting the medication and will diminish until it disappears completely. This resolution occurs as the antibiotics eliminate the Borrelia burgdorferi bacteria from the body.
With prompt antibiotic treatment, the skin lesions associated with Lyme disease heal without long-term consequences. The skin returns to its normal state without scarring. Successful treatment also signifies the eradication of the bacteria, preventing the progression to more severe, systemic complications.