Things You May or May Not Know About Head Lice

It’s sad to say but lice season is starting. *Groans from parents*.

By now, there are probably dozens of articles about how to treat lice, however I find a lot of articles lack detail on what exactly needs to be done. So I wrote this article to go over questions that many patients have asked me while in practice. I try to focus on what to do about lice, instead of “how to use lice shampoos” as this information can be easily obtained.

So let’s talk about how to deal with lice effectively, if you ever find yourself in this situation. *fingers crossed*

“What are lice and nits?”

Lice are insects that feed on blood on the scalp. They cling onto the roots of the hair close to the scalp surface where they can get a blood meal. Adult lice lay eggs called nits, which hatch around a week later and eventually grow to become adult lice. The remaining empty egg shells remain attached to the hair.

“I found nits on my child’s hair. Does my child have lice infestation?”

It depends.

Technically, diagnosis of lice is based on the discovery of a single moving louse (Knowles & Shear, 2019), not necessarily on the presence of nits. This is because it is difficult to definitely tell whether the nits are living or they are just empty egg shells, though the chance of active infestation is higher if the nits are closer to the scalp.

Realistically, lice move quickly and avoid light, so you probably will have trouble finding them if you part the hair manually. The easiest way of finding lice is a technique called “wet combing with conditioner” (Knowles and Shears, 2019). To do this:

  • Apply a generous amount of white-colored hair conditioner to hair.

  • Comb through the hair first with a normal hair comb to straighten the hair.

  • Comb through the hair from root to tip using a fine lice comb.

  • Wipe the conditioner that the lice comb pulls from the hair onto a white tissue.

  • Examine the tissue for lice.

  • You will have to repeat the technique 5 times in each part of the scalp.

The white color of the tissue and conditioner provides a good contrasting background to spot lice. The conditioner also makes it difficult for lice to hold onto the hair so that they will come off more easily. If you see lice on the tissue, you are dealing with an active infestation.

“I found a moving louse! How do I treat it?”

Using the “wet combing with conditioner” technique itself is a way to remove lice. Since it primarily removes lice not necessarily all the nits, this technique needs to be repeated regularly for a couple of weeks so that newly hatched lice can be consistently removed (Knowles & Shears, 2019; Fry et al, 2002). This is quite a time consuming technique but involves no chemicals.

Lice shampoos are also common choices, and can be very effective if used correctly. They either kill the lice directly as an insecticide (ie: Nix, Kwellada-P, R and C), or by physically damaging the lice (ie: NYDA, Resultz).

Since they kill lice, not reliably nits, the treatment usually needs to be repeated around a week after the first treatment to target those newly hatched lice. Combing the hair afterwards with a lice comb after each treatment every 2-3 days for 2 weeks further helps to remove nits and prevent the infestation from coming back. (“Head Lice”).

“Do I need to clean everything that person has contacted?”

Lice is spread primarily through close hair to hair contact. Adult lice do not fly or hop, but can only crawl.

In general, lice do not do very well away from the scalp. It has been studied that adult lice can survive up to 4 days away from the scalp, and nits can survive up to 10 days away from the scalp (Miller, P.F, 2018) although they are unlikely to hatch at room temperature.

That being said, if you are dealing with lice infestation, you do not have to sanitize all the clothing that individual has ever used, just focus on things that has been potentially contacted by head/hair (ie: pillow cases, clothing, bedding, towels, hats, combs) in the last 2-3 days (CDC,2016).

The best way to kill lice is heat, so putting the material in a dryer is effective. However if you don’t want to expose an item to heat, putting it away in a sealed bag for 2 weeks will kill any remaining lice/nits (Knowes and Shears, 2019; Speare et al, 2003).

You can also vacuum any carpeting, but if you are unable to or if that is not feasible it is okay, as the risk of getting lice from carpeting is very low (Speare et al, 2002).

“Why does lice keep coming back after treatment?”

There could be several reasons for this, which I have noticed in practice.

Do NOT use hair conditioner BEFORE treatment with lice shampoo, and do NOT re-wash the hair 1-2 days AFTER lice shampoo is removed. This is especially critical for insecticidal shampoos, as they have a residual effect up to 2 days after treatment. If you washed the hair shortly after treatment, this could have stopped the effect and significantly reduce the effectiveness of the lice shampoo.

Forgetting to treat family members or individuals with close contact. Some may choose to treat individuals sharing the same bed regardless whether they have confirmed infestation or symptoms.

Forgetting to repeat lice shampoo treatment with the proper timing. Re-treatment is ideally done after existing nits are hatched but before new eggs are laid, usually around a week after the first treatment. Missing the second treatment could mean missing a second batch of lice that was present originally. Lice could be resistant to insecticidal lice shampoo. If you completed a full course of insecticidal shampoo, combed all the hair you can, and the lice did not go away, then consider using a full course of non-insecticidal lice shampoos.

I hope this article is useful. Please feel free to share this article with anyone that you think may benefit.


Burgess, I.F. (2011). Head Lice. BMJ Clinical Evidence. 1703

Burkhart CN. (2003) Fomite transmission with head lice: A continuing controversy. Lancet;361(9352):99–100.

Center for Disease Control. (2016). Head Lice - Treatments. Retrieved from

Cummings, C., Finlay,J.C., MacDonald, N.E. (2018). Head Lice Infestation: A clinical Update. Peaediatric & Child Health. 23 (1), e18-e24.

Fry, F., Ibarra, J., Smith, J., & Wickenden, C. (2002). Wet combing to eradicate head lice. Journal of the Royal Society of Medicine, 95(12), 630–631.

“Head Lice: Diagnosis and Treatment”. Retrieved from

Knowles, S., Shears,N.H. (2019). Scabies and Lice. Compendium of Therapeutic Choices.

Miller,PF. (2018). Parasitic Skin Infection: Lice and Sabies. Compendium of Therapeutics for Minor Ailments.

Speare R, Cahill C, Thomas G. Head lice on pillows, and strategies to make a small risk even less. Int J Dermatol 2003;42(8):626–9.

Speare R, Thomas G, Cahill C. Head lice are not found on floors in primary school classrooms. Aust N Z J Public Health 2002;26(3):208–11.

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