It makes their chitin coat nice and shiny. No, it doesn't kill them or the eggs. It makes your hair nice and slick, and sometimes it's easier to pick off each individual louse, and comb off the nits. But honestly, if you have lice and want to get rid of them, it's best to just use the kit made for the purpose. You can buy it in stores, and the health departments often give them away free of charge. Just get one and use it, save the mayo for a sandwich.