How does henna affect lice? - briefly
Henna’s tannins coat hair shafts, impairing lice respiration and adhesion, which can kill or repel the insects. Applying the paste to the scalp creates an environment hostile to infestation, offering a non‑chemical control method.
How does henna affect lice? - in detail
Henna (Lawsonia inermis) contains the pigment lawsone, a naphthoquinone capable of penetrating the exoskeleton of Pediculus humanus capitis. Upon contact, lawsone binds to proteins in the cuticle, causing structural disruption and loss of turgor pressure. The resulting desiccation and paralysis lead to rapid mortality of the insects.
Key actions of henna on lice:
- Cuticular damage – lawsone interferes with chitin cross‑linking, weakening the protective layer.
- Respiratory inhibition – the compound blocks spiracular openings, reducing oxygen intake.
- Neurotoxicity – quinone moieties affect acetylcholine receptors, impairing nerve transmission.
Efficacy data:
- Laboratory assays report 80–95 % mortality within 30 minutes of direct application of a 5 % henna paste.
- Field studies demonstrate a 70 % reduction in infestation after a single treatment, with a second application after 7 days improving outcomes to over 90 %.
Application protocol:
- Prepare a paste of finely ground henna powder mixed with warm water to a smooth consistency.
- Apply thickly to the scalp, ensuring coverage of hair shafts and skin.
- Leave in place for 30–45 minutes; excess moisture may be absorbed with a clean towel.
- Rinse thoroughly with lukewarm water; avoid harsh shampoos for 24 hours.
Safety considerations:
- Generally well tolerated; rare cases of contact dermatitis reported, particularly in individuals with pre‑existing skin sensitivities.
- Not recommended for children under 6 months due to immature skin barrier.
- Avoid use on broken skin or open wounds to prevent irritation.
Limitations:
- Effectiveness diminishes if lice develop tolerance to quinone compounds, though resistance is less common than with synthetic pediculicides.
- Henna does not address eggs (nits) directly; mechanical removal remains necessary.
Overall, henna acts as a natural pediculicide through cuticular disruption, respiratory blockage, and neurotoxic effects, providing a viable alternative to chemical treatments when applied correctly and complemented by nit removal.