Why does a tick bite become red? - briefly
The bite site turns red because tick saliva contains anticoagulants and irritant proteins that provoke a local inflammatory response, causing vasodilation and increased blood flow. The body's immune reaction to these foreign substances can amplify the redness.
Why does a tick bite become red? - in detail
A tick’s mouthparts penetrate the skin and inject saliva that contains anticoagulants, anti‑inflammatory agents, and various proteins. The body recognises these foreign substances as threats, triggering an immune reaction. Histamine released by mast cells dilates blood vessels, allowing immune cells to reach the site; the resulting vasodilation produces the characteristic redness.
The redness may be amplified by:
- Allergic response to tick salivary proteins, which can cause a pronounced local erythema.
- Inflammatory cascade initiated by cytokines such as interleukin‑1 and tumor‑necrosis factor, promoting further vascular permeability.
- Secondary bacterial infection if the bite is scratched or the skin barrier is breached, leading to additional inflammation and redness.
- Pathogen transmission (e.g., Borrelia burgdorferi, Anaplasma), which can provoke a more extensive immune response and a larger erythematous area.
The intensity and duration of the red halo depend on individual sensitivity, the tick’s feeding duration, and whether a pathogen was introduced. In most cases, the redness subsides within a few days as the inflammatory response resolves, but persistent or expanding erythema warrants medical evaluation for possible infection.