How does a lice bite itch? - briefly
When a louse pierces the skin, its saliva introduces proteins that stimulate histamine release, creating a localized inflammatory response. The ensuing swelling and irritation generate the characteristic itch.
How does a lice bite itch? - in detail
Lice bite the skin to feed on blood, injecting a small amount of saliva that contains anticoagulants and enzymes. The saliva is recognized as a foreign protein, triggering the body’s immediate immune response. Mast cells release histamine and other mediators, which bind to sensory nerve endings and produce the characteristic pruritus.
The itch develops in stages:
- Initial contact: Mechanical puncture stimulates cutaneous nociceptors, causing a mild, fleeting sensation.
- Saliva exposure: Proteins in the louse’s secretions activate the complement system and attract inflammatory cells.
- Histamine release: Mast cells degranulate, flooding the area with histamine, prostaglandins, and leukotrienes.
- Nerve activation: Histamine binds to H1 receptors on C‑fibers, amplifying the itch signal to the spinal cord and brain.
- Delayed reaction: Some individuals develop a secondary, more intense itch 12–24 hours later as adaptive immunity produces specific IgE antibodies.
Factors influencing intensity include the number of bites, individual sensitivity, and the presence of secondary infection from scratching. Antihistamines, topical corticosteroids, and soothing agents such as calamine can mitigate the response by blocking histamine receptors or reducing inflammation.