Understanding Nix and Its Mechanism
Nix is an over-the-counter (OTC) medication used to treat head lice (pediculosis) [1.4.2]. Its active ingredient is permethrin 1%, a synthetic chemical that acts as a neurotoxin to lice [1.4.2, 1.6.5]. Permethrin works by disrupting the sodium channels of louse nerve cell membranes. This disruption leads to delayed repolarization and eventual paralysis and death of the parasites [1.6.2, 1.6.6]. A significant feature of Nix Crème Rinse is its residual effect; the active ingredient can remain on the hair for up to two weeks, allowing it to kill newly hatched lice from any missed nits (eggs) [1.4.3]. This persistent activity is a key factor in its effectiveness and helps protect against reinfestation during that period [1.4.3].
Initial Signs of an Effective Treatment
Knowing if the treatment has been successful begins in the hours immediately following the application. It's crucial to follow the product's directions precisely, leaving it on the hair for the recommended 10 minutes and avoiding conditioner use, which can interfere with the medication [1.4.5, 1.5.2].
Immediate Post-Treatment Checks (8-12 hours):
- Slow or Dead Lice: According to the Centers for Disease Control and Prevention (CDC), seeing lice that are moving slowly 8 to 12 hours after treatment is a sign the medication is working [1.2.4, 1.4.1]. The permethrin takes time to kill all the lice. Finding dead lice is also a good sign [1.2.2].
- Absence of Active Lice: If, after 8-12 hours, lice appear just as active as before treatment, it may indicate the treatment was not effective [1.2.4, 1.7.4]. This could be due to improper application or, in some cases, resistance to the medication [1.2.3, 1.4.3].
Long-Term Verification: Combing and Observation
Verifying that the lice infestation is completely gone is a process that takes two to three weeks of diligent follow-up [1.2.4, 1.5.3].
The Role of the Nit Comb
The most critical post-treatment step is combing the hair with a fine-toothed nit comb. This should be done every 2-3 days for 2-3 weeks to remove dead lice, dying lice, and nits [1.2.4, 1.5.3]. This process helps prevent self-reinfestation and allows you to monitor the treatment's success [1.5.3].
Differentiating Live Nits vs. Dead Nits
Recognizing the difference between viable (live) and non-viable (dead or empty) nits is essential for peace of mind. Continuing to find nits does not automatically mean the treatment failed.
- Location: Live nits are typically found very close to the scalp (within 1/4 inch), where the warmth is necessary for them to incubate and survive [1.3.1, 1.3.6]. Nits found further down the hair shaft are likely dead, hatched, or from a previous infestation that has grown out with the hair [1.3.1, 1.3.2].
- Color and Shape: Live nits are often translucent to brown and have a uniform, oval shape [1.3.1, 1.3.3]. Dead nits may appear yellowish, brown, or white and can look shriveled or irregular [1.3.1]. Hatched nits are typically clear or white shells [1.3.3].
- Ease of Removal: Live nits are cemented firmly to the hair shaft and are difficult to remove. Dead nits become easier to dislodge over time as the adhesive weakens [1.3.1].
If after three weeks of regular checks you find no live, crawling lice, it is safe to assume the treatment was successful, even if some old nit casings remain [1.2.3].
Signs of Treatment Failure vs. Success
| Sign | Treatment Is Likely Working | Treatment Is Likely Failing |
|---|---|---|
| Lice Activity (8-12 hours) | Lice are dead or moving very slowly [1.2.4]. | Lice are as active as they were before treatment [1.2.4]. |
| Nit Location | Nits found are more than 1/4 inch from the scalp [1.3.6]. | New nits are found close to the scalp [1.7.1]. |
| Itching | Itching may persist for up to a week as an allergic reaction, but it should gradually decrease [1.7.1]. | Intense itching continues or worsens after a week [1.7.1]. |
| New Sightings (After 7 days) | No new live lice are found during combing checks [1.2.2]. | Live, active lice are found 7 days or more after the initial application [1.2.1]. |
When to Consider Re-Treatment or See a Doctor
Nix instructions often recommend a second application on day 7 or 9 to kill any lice that may have hatched from nits missed in the first round [1.2.1, 1.4.5]. This is a standard part of the process for many OTC treatments [1.4.2].
However, if you still see live, active lice 7 days or more after the first treatment, a second application of Nix is advised [1.2.1]. If live lice are still present after a second properly applied treatment, it may be time to consult a healthcare provider [1.2.4]. This could indicate a case of "super lice," which are resistant to traditional pesticide treatments like permethrin, or a re-infestation from an outside source [1.2.7, 1.4.3]. A doctor can prescribe alternative treatments that may be more effective [1.2.3].
Conclusion
Ultimately, knowing Nix is working is a multi-step process. It starts with observing dead or dying lice shortly after application, followed by diligent combing and monitoring for two to three weeks. The key indicators of success are the complete absence of live, crawling lice and the lack of any new nits appearing close to the scalp. While finding old nits can be unsettling, their presence far from the scalp is a normal part of hair growth after a successful treatment. If live lice persist after a second treatment, seeking professional medical advice is the best course of action.
For more information from a trusted source, you can visit the CDC's page on head lice treatment.
