Lice

If you don't want to use lice shampoo, I believe putting a few drops of tea tree oil in your shampoo is a good way to get rid of them.
I unfortunately got lice as a teenager from my cousin and they didn't even tell my parents right away that their daughter had it.
Anyways, long story short. I used tea tree oil in my shampoo and it got rid of the lice. Doing it as a preventative measure shouldn't hurt.

The bottles of lice treatment shampoo have very clear warnings NOT to use as a preventative measure only for full blown infestations ... they are highly toxic you do not want to apply that to your skin just as a precaution and if you DO and they do not have lice yet you risk if you DO get them having them be 'resistant' to the treatment!

I second or third the suggestion of using a TEATREE oil as a preventative measure ... I have used this weekly on my hair for all the decades I have been in the field and we have never had lice come through our home despite having had it in centre year after year and being 'exposed' to it ... but even Teatree oil while 'natural' is still harsh plant do not use it more than 'necessary' to prevent lice or as a treatment for it ... aka I would not use it daily preventative cause the plant has been shown to be hard on the kidney's when constantly exposed to it :(

Yes tea tree oil is a good preventative....a few drops in your shampoo will likely keep them away ....

I had lice a few times as a child (playing with the stray animals didn't help and I had super long hair). It's not fun..