Why does the head constantly itch because of lice? - briefly
Lice feed on scalp blood, injecting saliva that provokes an allergic inflammatory response, which manifests as intense itching. Continuous feeding and accumulation of lice waste sustain the irritation.
Why does the head constantly itch because of lice? - in detail
Lice infestation triggers a cascade of physiological responses that produce continuous scalp irritation. The insects attach to hair shafts and pierce the skin to feed on blood. Their saliva contains anticoagulants and enzymes that the body recognizes as foreign, prompting an immediate immune reaction. Histamine release at the bite sites causes vasodilation, swelling, and the characteristic itching sensation.
Repeated feeding deepens the inflammatory response. Each bite introduces additional saliva, sustaining histamine production and sensitizing surrounding nerve endings. Over time, the scalp becomes hyper‑responsive, so even light contact with hair or air movement can provoke itching.
Secondary factors amplify the discomfort:
- Mechanical irritation: The movement of lice through the hair creates friction that damages the stratum corneum, exposing nerve endings.
- Allergic sensitization: Some individuals develop heightened immune sensitivity to lice proteins, resulting in stronger pruritic reactions after only a few bites.
- Microbial colonization: Scratching compromises the skin barrier, allowing bacteria and fungi to colonize, which further inflames the area and perpetuates the itch‑scratch cycle.
- Moisture accumulation: Lice thrive in warm, damp environments; the resulting increase in scalp humidity can weaken the skin’s protective layer, making it more prone to irritation.
The combination of saliva‑induced histamine release, mechanical damage, allergic sensitization, and possible secondary infection explains why the scalp remains persistently itchy during an infestation. Effective treatment must eliminate the parasites, reduce inflammation, and restore skin integrity to break the cycle.