I treated a little girl ( about 10 years old) for head lice. She had clumps of lice bugs and nits. I would estimate that she probably had head lice for about 1 year. The family been treating the child for head lice all along but obviously not getting everything out. The family been using over the counter products to treat but none of it worked. So it is very important to use products that are efficient and works. If not you can be dealing with head lice for months or years.