Head lice: what causes them to appear? - briefly
Head lice infestations arise from direct head‑to‑head contact with an infested individual or from sharing personal items—combs, hats, hair accessories—that harbor viable nits. Warm, crowded settings and close interpersonal interaction increase transmission, while personal cleanliness does not prevent infestation.
Head lice: what causes them to appear? - in detail
Head lice infestations begin when adult females lay eggs (nits) on hair shafts close to the scalp. The eggs hatch within 7–10 days, releasing nymphs that mature into reproductive adults after another 9–12 days. This rapid life cycle creates a population capable of expanding quickly once transmission occurs.
The most common route of transmission is direct head‑to‑head contact. Children in schools, day‑care centers, and camps frequently engage in activities that bring their scalps together, providing the sole opportunity for lice to move from one host to another. Sharing personal items—combs, brushes, hats, hair accessories, or headphones—can also transfer eggs or live insects, though this is a secondary pathway.
Several risk factors increase the likelihood of an outbreak:
- Age 6 months to 11 years, when close contact is frequent.
- Environments with high population density, such as classrooms or shelters.
- Limited access to regular hair‑care resources or proper laundering facilities.
- Presence of a previous infestation in the household, indicating a reservoir of eggs.
Biological preferences of the parasite further explain its appearance. Head lice thrive in temperatures between 30 °C and 34 °C, conditions typical of the human scalp. They feed on blood, attracted by the warmth and moisture of the skin. The presence of scalp oil and a moderate level of hair length facilitate egg attachment and concealment from detection.
Prevention relies on minimizing opportunities for transfer. Recommended actions include:
- Educating children about avoiding head contact during play.
- Restricting the exchange of headgear, combs, and other personal grooming tools.
- Conducting regular visual inspections of hair, especially after known exposure.
- Washing potentially contaminated items in hot water (≥ 60 °C) and drying on high heat.
Understanding these mechanisms clarifies why infestations arise and guides effective control strategies.