A good (and inexpensive) alternative to chemical treatments is mixing Tea Tree Oil into your shampoo if it is a continual problem. To treat a current outbreak mix 10-12 drops Tea Tree Oil with 1 cup olive oil and apply to affected person. Put a shower cap on them and leave for an hour or so.
Comb out with fine comb. This not only kills the lice (without chemicals), but it gives the hair shine.