Why do lice cause itching? - briefly
Lice bite the scalp and inject saliva that contains anticoagulant proteins, provoking an allergic response and histamine release that produces itching. The ensuing inflammation around the feeding sites amplifies the sensation of itch.
Why do lice cause itching? - in detail
Lice feed on blood by piercing the scalp with their mouthparts. During this process they inject saliva that contains anticoagulants and proteolytic enzymes. These substances are recognized by the host’s immune system as foreign, prompting an immediate inflammatory response.
The inflammatory cascade involves the release of histamine from mast cells. Histamine binds to sensory nerve endings in the epidermis, generating the characteristic pruritic sensation. The reaction is localized, producing erythema and swelling around each attachment site.
Mechanical factors also contribute. Repeated movement of the insects along hair shafts creates microabrasions. The physical irritation of the cuticle stimulates additional nerve fibers, amplifying the perception of itch.
A secondary effect arises when scratching disrupts the skin barrier. Breaks in the epidermis allow opportunistic bacteria to colonize, leading to further inflammation and persistent itching.
Key mechanisms can be summarized:
- Salivary proteins act as allergens, triggering histamine release.
- Histamine activates cutaneous nerve endings, producing pruritus.
- Continuous crawling and feeding cause microtrauma to the scalp.
- Scratching compromises the skin barrier, facilitating bacterial invasion and prolonging the itch response.
Understanding these processes clarifies why infestations provoke intense discomfort and underscores the importance of prompt eradication and proper scalp hygiene.