We guarantee that if you follow the directions, LiceKiller products will kill all the lice you are dealing with. We also guarantee that you will probably have a Re-Infestation. When that happens, use LiceKiller immediately (MAKE SURE YOU ORDER ENOUGH PRODUCT TO HAVE SOME LEFT OVER FOR THE RE-INFESTATIONS THAT WILL PROBABLY COME). Do NOT wait 7-10 days between treatments. If you find you have been infested with a species of head lice that does not die when treated with LiceKiller, contact us immediately and we will send you a different formula absolutely free. We will work with you to eradicate that species and warn others in your area about it.