What do lice on hair fear? - briefly
Lice are eliminated by exposure to temperatures above 50 °C, by insecticidal treatments such as permethrin or pyrethrin shampoos, and by meticulous combing that physically removes them from the hair.
What do lice on hair fear? - in detail
Lice that inhabit human hair are highly sensitive to environmental changes and chemical agents. Their survival depends on maintaining specific conditions; any deviation can be lethal or provoke avoidance behavior.
Key threats include:
- Insecticidal shampoos and lotions – active ingredients such as permethrin, pyrethrins, or dimethicone disrupt the nervous system or suffocate the insects, leading to rapid mortality.
- Extreme temperatures – exposure to heat above 50 °C (122 °F) for a few minutes denatures proteins, while temperatures below –5 °C (23 °F) cause ice crystal formation that ruptures cells.
- Desiccation – prolonged absence of moisture, especially in dry climates or after thorough washing, results in loss of body fluids and death within hours.
- Mechanical removal – fine-toothed combs or manual extraction physically detach lice from the scalp, preventing feeding and reproduction.
- Host absence – lice rely exclusively on human blood; a prolonged period without a host (e.g., during extensive hair removal or prolonged isolation) leads to starvation and death after 1–2 days.
- Predatory arthropods – mites such as Cheyletiella or predatory beetles introduced inadvertently can prey on lice, reducing their numbers.
- Chemical residues in hair products – certain conditioners, oils, or styling agents alter the cuticle’s surface tension, making it difficult for lice to attach and move, thereby discouraging colonization.
Each factor interferes with one or more physiological processes essential for lice: nerve transmission, water balance, respiration, or feeding. Understanding these vulnerabilities informs effective control strategies and explains why lice avoid environments that present any of the listed hazards.