I am not a real doctor. That said, I cannot find any indication of human head lice causing anemia. In fact, the only long term health consequencesof a head lice infestation seem to be: potential infection if excessive scratching breaks the skin of the scalp, loss of sleep due to itching and irritability due to loss of sleep.
Look at the math - a typical louse has about 3 blood meals per day, each averaging about 0.0000983 mL of blood. Take the daily blood meal per louse average of 0.0002949 mL of blood multiplied by the typical infestation of ~30 lice equals 0.0088470 mL of blood per day, or about .000002 pint. To account for .01 pint of blood per day, a still miniscule amount, would require in the neighborhood of 18,000 lice. If you have 18,000 lice on your head, go immediately to the zoo. You’ll be the most popular primate in the exhibit.
When Moon Unit brought home more than memories from summer camp one year (they do head checks but apparently it was rather cursory), we did the OTC stuff (Nix, I think) - which killed a few. But two days later I was doing a thorough comb-through and found a live critter that looked too mature to have just hatched in the past 48 hours, so clearly the OTC stuff wasn’t effective enough.
While I did follow the instructions and repeat the treatment after a week, in the meantime every 48 hours I did a very through combthrough after dousing her head in olive oil or similar, letting it sit for a while as she wore a disposable shower cap, then sectioning and combing with a metal lice comb. I used plastic hair clips to hold back areas I was not working on. The oil doesn’t kill them but it does slow them down, meaning they can’t escape, and it loosens their grip on the hair.
It was a pain - but I don’t think I found any more live critters. The comb-throughs probably also helped remove any nits - the oil may have loosened their grip on her hair, or maybe it was just the mechanical action of the comb. Her scalp was in great shape after the treatments as well.
And of course I caught them. I had my husband go through my hair and he saw nothing. The very next day I took the metal comb to it and quite literally on the second stroke I found a resident. So he had to help me comb through MY hair periodically. I also did the olive oil treatment. It’s a pain because you really do have to shampoo 2-3 times to get it all out afterward; one day I must not have done a thorough enough job and the entire next day at work I could smell it.
Supposedly the “burn everything in sight” approach to housecleaning is overkill. Certainly, wash anything that touches her head (hats etc.) and we did wash her pillowcases every day, but the critters simply don’t live all that long when away from their host.
