Why does the head itch heavily with lice? - briefly
Head lice attach to hair shafts, pierce the scalp, and inject saliva containing irritants that trigger an allergic reaction in many individuals. The ensuing inflammation and histamine release cause intense itching.
Why does the head itch heavily with lice? - in detail
Intense scalp itching during a lice infestation results from several physiological mechanisms.
The primary trigger is the saliva injected by the insects while feeding. Salivary proteins contain antigens that stimulate a local immune response. Histamine release from mast cells produces the characteristic pruritus.
A secondary factor is the mechanical irritation caused by the movement of the parasites across the skin surface. The legs and claws of the insects abrade the epidermis, creating micro‑abrasions that further sensitize nerve endings.
Additional contributors include:
- Bacterial colonisation of the micro‑abrasions, leading to mild infection and heightened inflammatory signalling.
- Allergic sensitisation in some individuals, where repeated exposure to lice antigens amplifies the histamine response.
- Accumulation of nits and dead lice, which act as foreign bodies and maintain constant stimulation of cutaneous receptors.
The nervous system translates these peripheral signals into the sensation of itching. C‑fibers convey the itch stimulus to the spinal cord, where it is processed in the dorsal horn and relayed to the brain’s somatosensory and limbic areas, producing the urge to scratch.
Scratching aggravates the condition by disrupting the skin barrier, permitting further entry of irritants and pathogens, and perpetuating the itch‑scratch cycle.
Effective management therefore targets the underlying infestation, reduces inflammatory mediators, and prevents secondary infection.