There are several reasons lice may remain unaffected after treatment. With any head lice treatment, all lice and nits (eggs) must come in full contact with the product. Lice can move quickly to avoid contact with the shampoo, lotion or gel. Reinfestation from environmental contact (i.e. infested hats, pillows, stuffed animals, etc.) can also occur. Missing any nits when combing out can trigger a reinfestation.