What causes head itching after lice appear? - briefly
Itching occurs because lice bite the scalp and inject saliva that triggers an allergic or inflammatory response, while their droppings further irritate the skin. The combined effect of these secretions and mechanical irritation leads to the characteristic pruritus.
What causes head itching after lice appear? - in detail
The itching sensation that develops on the scalp once head‑lice infestations are present stems from several physiological reactions.
First, the insects inject saliva while feeding on blood. Salivary proteins contain antigens that trigger a localized immune response. Histamine release in the skin produces pruritus and redness. The intensity of the reaction varies with individual sensitivity; some people experience mild irritation, while others develop a pronounced allergic response.
Second, the mechanical activity of the lice contributes to discomfort. Their movement through hair shafts and attachment to the scalp creates micro‑abrasions and stimulates nerve endings. Repeated crawling and feeding increase friction, which amplifies the itch.
Third, secondary bacterial colonisation often follows the primary infestation. Small cuts created by lice or by scratching become entry points for skin flora such as Staphylococcus aureus. Bacterial metabolites further inflame the area, sustaining or worsening the pruritic feeling.
Fourth, the psychological urge to scratch intensifies the problem. Scratching damages the epidermis, releases additional inflammatory mediators, and can lead to a cycle of itching‑scratch‑itch.
Key factors that influence the severity of the symptom include:
- Host immune status – heightened sensitivity to lice saliva accelerates histamine release.
- Duration of infestation – prolonged exposure increases cumulative saliva deposition and skin irritation.
- Hair type and density – thicker hair traps more insects, raising the likelihood of mechanical irritation.
- Concurrent skin conditions – eczema or psoriasis predispose the scalp to stronger reactions.
Effective management requires eliminating the parasites and addressing the inflammatory response. Over‑the‑counter pediculicides remove the insects, while antihistamines or topical corticosteroids reduce allergic itching. Maintaining scalp hygiene, avoiding excessive scratching, and treating any secondary bacterial infection with appropriate antibiotics complete the therapeutic approach.