I have had head lice three times in my 41 years of life. Once when I was 20 and again when I was 40. For some reason I could not get rid of them the last time until I used this shampoo. One, it does kill an infestation if you use everyday for 2 weeks. Two, it is a great preventative. You do not have to use everyday but I strongly recommend having it on hand. Instructions are simple: Apply normal shampoo amount to hair and lather; rinse. Apply again but leave on hair for 3 minutes; rinse. The shampoo softens any nits you have so they don't hatch and prevents a louse from laying eggs. Does have a strong smell but it goes away as hair dries. If your child comes home from school with a note about head lice outbreak in his/her school, jump in the shower and do above and you'll be fine. This shampoo also repairs damage from previous infestations. Effectiveness Works the BEST! Scent Kind of a strong licorice smell but it dissipates as hair dries.