A much better treatment and preventative for head lice than chemical
rinses is rosemary oil.  Seems the little buggers are repelled by the
stuff.  There are shampoos and creme rinses containing this oil.  The
most important thing is to put lots of the conditioner on the hair, wait
and comb with the finest little metal comb (plastic doesn't work as
well.) I learned this little trick from a kindergarten teacher.  It
really works.  I do it as a preventative once a week and haven't had any
problems with the kids in years.  Susan