How long should a lice shampoo be left on the head? - briefly
Apply the shampoo and keep it on the scalp for approximately «10 minutes» before rinsing. Follow the specific directions on the label for any variation.
How long should a lice shampoo be left on the head? - in detail
The effectiveness of a lice‑removing shampoo depends on the contact time specified by the product’s active ingredient. Most over‑the‑counter formulations contain either permethrin (1 %) or pyrethrin‑based compounds, and the label instructs a minimum exposure period of 10 minutes. Some prescription options, such as malathion 0.5 %, require a longer duration, typically 12 minutes, to achieve complete toxicity against the parasite.
For optimal results, follow these steps:
- Apply the shampoo to dry hair, ensuring thorough saturation from scalp to tips.
- Massage gently for 30 seconds to distribute the solution evenly.
- Maintain the instructed exposure time without rinsing; set a timer to avoid under‑ or over‑exposure.
- After the elapsed interval, rinse the hair with warm water for 2–3 minutes, then repeat the washing cycle if the product label recommends a second treatment after 7–10 days.
If the shampoo contains a non‑neurotoxic ingredient, such as dimethicone, the required contact time may be shorter, often 5 minutes, because the mechanism relies on physical coating rather than chemical toxicity. In such cases, the label will explicitly state the reduced duration.
Adherence to the manufacturer’s timing is critical. Insufficient exposure may leave viable lice, while excessive exposure can irritate the scalp. When uncertainty exists, consult the product’s instructions or a healthcare professional to confirm the precise interval for the specific formulation.