Why does the head itch when there are lice? - briefly
Lice bite the scalp and inject saliva that contains irritants, provoking an allergic reaction and inflammation that causes itching. Their presence and movement also mechanically stimulate nerve endings, adding to the sensation.
Why does the head itch when there are lice? - in detail
Lice feed on blood by piercing the scalp with their mouthparts. During each bite they inject saliva that contains anticoagulants and proteins. The body’s immune system recognizes these foreign proteins and releases histamine, which produces the sensation of itching.
The mechanical presence of the insects also contributes to irritation. Their claws cling to hair shafts, and their movement across the skin creates micro‑abrasions. These tiny wounds stimulate nerve endings, adding to the pruritic response.
A secondary factor is the potential for bacterial contamination. Scratching breaks the skin barrier, allowing skin‑resident bacteria to invade, which can cause localized inflammation and further increase discomfort.
Key mechanisms underlying scalp pruritus in a lice infestation:
- Salivary antigen exposure: triggers histamine release and allergic reaction.
- Physical abrasion: movement of the parasites damages the epidermis.
- Secondary bacterial infection: results from skin trauma caused by scratching.
- Neurogenic inflammation: nerve fibers react to both chemical and mechanical stimuli, amplifying the itch signal.
Effective treatment must address each component: eradicate the parasites, reduce histamine activity with anti‑itch agents, and maintain scalp hygiene to prevent infection.