Glad you asked! The itch you develop from lice is a result of an allergic reaction your body has to the bite. It typically takes 4–6 WEEKS (people are really surprised to hear this) after you are infected for the itch to begin. People come into my lice center thinking because their child recently started itching that it’s a new case and are shocked to hear it’s likely been at least 4 weeks. For answers to all commonly asked questions on lice, please visit our site: Learn how to treat lice & get rid of them | Lice Nannies USA.