Why do flea bites itch heavily and for a long time? - briefly
Flea saliva contains anticoagulants and proteolytic enzymes that trigger a strong histamine release, producing intense, prolonged itching. The immune response to these proteins keeps the inflammation active for days after the bite.
Why do flea bites itch heavily and for a long time? - in detail
Flea saliva contains a complex mixture of proteins, anticoagulants, and enzymes that trigger the body’s immune response. When a flea pierces the skin, these substances are injected along with the blood meal, causing immediate irritation.
The primary mechanisms behind the pronounced and lasting pruritus are:
- Histamine release: Mast cells detect foreign proteins and degranulate, releasing histamine. Histamine binds to nerve endings, producing the characteristic burning sensation and swelling.
- Protease activity: Enzymes in the saliva break down skin proteins, exposing additional antigenic sites and prolonging the inflammatory cascade.
- Anticoagulant effect: Substances that prevent clotting keep the bite site open, allowing continuous exposure to irritants and delaying wound closure.
- Sensitization: Repeated exposure can lead to IgE‑mediated hypersensitivity. Subsequent bites provoke a stronger, faster response, intensifying itching and extending its duration.
- Neurogenic inflammation: Nerve fibers release neuropeptides such as substance P, which amplify vasodilation and attract more immune cells to the area.
These processes generate a localized edema that traps inflammatory mediators, sustaining the itch for hours to days. Secondary scratching damages the epidermis, introduces bacteria, and further fuels the cycle of inflammation, often lengthening the discomfort.
Effective management targets each step: antihistamines block histamine receptors, topical corticosteroids reduce cytokine production, and cold compresses constrict blood vessels to limit mediator spread. Preventive measures—regular flea control on pets and environments—eliminate the initial cause and reduce the frequency of bites.