One of the myths about head lice is that they live in dirty hair. They can, but they prefer clean hair because it's harder to move around in dirty hair.
My kids had to deal with head lice, once. My daughter managed to bring some home from school with her, we're not sure how. The school nurse eventually figured out the carriers were sisters and began dealing with the outbreak. Affected children were not allowed to return until treated successfully at home. But, we didn't know our daughter was affected until much later.
Meanwhile, my daughter introduced the little buggers to her brothers, while the three were head-to-head on the back seat of the van watching a movie during our cross-country trip to visit the grandparents for the holidays. We didn't discover the problem until our arrival. Guess who had them! It was the most frightening experience I've ever had.
Thank goodness my BIL is a pharmacist and he promptly armed us with all the appropriate treatments. We spent the holiday constantly doing laundry and washing every towel and sheet in the house (just in case). That house ended up the cleanest it had ever been in years.
No sooner did our daughter return to school, she came home with more little buggers. It seems the sisters who were the source the first time around were the source, again. Their poor mom! They were withdrawn from the school for an extended period of time until they could be declared infestation free. Poor little girls!
Well, at least we knew what we had to do. But, I was more concerned about the potential toxic affect upon my kids by treating them so soon after the first infestation. Thank goodness the school nurse diligently checked the kids at school and we didn't have to undergo a third round. Poor nurse!