There are some that are 7 days ... Depends on the brand that you use ....and it takes 10 days for an egg to hatch if the parent misses just one then you have a whole new out break and the last thing I want to do is sanitize for lice again because I allowed a child back .... Also I think of it from the parents of children who didn't get it that I am protecting from another outbreak..... I don't agree with the school system and the fact that they dont have any exclusion and here in Ottawa they don't even do head checks anymore .... I don't feel they are protecting my children because the shampoo treatment is highly toxic and not something I want to apply to my child's head just because they were not kept home till after the second treatment