What itches during a lice infestation? - briefly
Itching results from an allergic response to the saliva injected by the parasites and the mechanical irritation of their bites. Inflammation of the scalp skin intensifies the sensation.
What itches during a lice infestation? - in detail
Lice feed on blood by piercing the skin with their mouthparts. The injection of saliva, which contains anticoagulants and proteins, triggers a local immune response. Histamine release around the bite site produces the characteristic pruritus. Repeated bites increase the concentration of these substances, intensifying the sensation.
The itch may also arise from secondary effects:
- Mechanical irritation from the insects moving through hair shafts.
- Microabrasions caused by the mandibles during feeding.
- Bacterial colonization of scratched lesions, leading to inflammation.
- Allergic sensitization; some individuals develop heightened reactivity after repeated exposure.
Head lice (Pediculus humanus capitis) tend to bite the scalp, where skin is thin and richly innervated, resulting in focal itching that often appears behind the ears, at the nape, and along the hairline. Body lice (Pediculus humanus corporis) reside in clothing and bite exposed skin, producing widespread, sometimes more severe pruritus, especially on the shoulders, waist, and lower abdomen.
Factors influencing itch intensity include:
- Personal sensitivity to lice saliva.
- Duration of infestation; longer exposure increases cumulative saliva load.
- Frequency of scratching, which can damage the epidermis and amplify nerve stimulation.
- Co‑existing skin conditions (e.g., eczema) that lower the threshold for irritation.
Effective control of the sensation requires eliminating the parasites, minimizing skin trauma, and, when necessary, applying topical antihistamines or corticosteroids to reduce inflammation. Prompt treatment prevents secondary infection and limits the chronic cycle of itch and scratch.