Head lice, known scientifically as Pediculus humanus capitis, are tiny, wingless insects that live on the human scalp and feed on blood. These common infestations occur frequently, particularly among school-aged children. Understanding how contagious lice are after treatment can help alleviate concerns and guide appropriate actions.
Contagiousness After Treatment
An individual properly treated for head lice is generally no longer contagious. Most over-the-counter and prescription treatments are designed to kill live lice, which are the primary means of transmission. Head lice spread mainly through direct head-to-head contact, as they cannot jump or fly. Once live, mobile lice are eliminated from the scalp, the risk of transmission significantly decreases.
A common concern involves nits, or lice eggs, which may remain in the hair after treatment. While nits are often visible, they are typically dead or too far from the scalp to hatch. Nits are firmly attached to the hair shaft and do not directly transmit lice. Only live, crawling lice can infest a new host. The critical factor in determining contagiousness is the absence of live, active lice.
Confirming Treatment Effectiveness
Confirming treatment success involves re-checking the hair and scalp for live, crawling lice. Inspect the scalp 8 to 12 hours after the initial treatment to ensure lice are dead or significantly less active. A thorough visual inspection, often aided by a fine-toothed comb, confirms treatment success. If live lice are still active and appear unaffected, the treatment may not have worked.
A follow-up check is typically recommended 7 to 9 days after the first treatment. This timing is important because any nits that survived the initial treatment and hatched into nymphs can then be eliminated before they mature and lay new eggs. Finding nits, especially those located more than 1/4 inch from the scalp, usually indicates either empty egg casings or nits that are unlikely to hatch, and these do not signify an active, contagious infestation.
Preventing Re-infestation
After confirming successful treatment and the absence of live lice, steps can be taken to prevent re-infestation. Wash bedding, clothes, and other items that came into contact with the infested person in the two days before treatment. Machine wash these items in hot water (130°F or higher) and dry on a high heat setting. Clean combs and brushes by soaking them in hot water (at least 130°F) for 5 to 10 minutes.
While extensive environmental cleaning is often not necessary, as head lice cannot survive long off a human host (typically less than two days), vacuuming floors and furniture may be done. Avoiding direct head-to-head contact with others is a primary way to prevent re-infestation, as this is the most common method of transmission. Discourage sharing personal items such as hats, scarves, and hair accessories.
When to Re-treat
Re-treatment may be necessary if live lice are found on the scalp after the initial application. If live lice are still present or as active as before treatment 8 to 12 hours after the first application, the treatment may have failed. Many over-the-counter and prescription treatments recommend a second application 7 to 9 days after the first to target any newly hatched lice before they can reproduce.
Follow the specific instructions provided with the lice treatment product for proper timing and application. If repeated treatments are unsuccessful or concerns arise about potential insecticide resistance, consult a healthcare professional for guidance on alternative treatments or prescription options.