NYDA (92% Dimeticone Dual Formula), scientifically proven to kill head lice in one minute and their eggs (nits) in eight hours , is a non-greasy lotion with a light citrus fragrance. You apply it to scalp and hair with the pump spray supplied with the bottle. NYDA is a physical treatment, not a pesticide, this means you will not be using harmful chemical to poison the head lice. With its unique formula, NYDA coats the head louse's body and rapidly penetrates its respiratory system, blocking its airways. This suffocates the louse,which is which is killed in less than a minute. In the same manner, NYDA kills lice eggs (nits), but it takes more time. To ensure efficacy on eggs, each application of NYDA should be left in the hair for eight hours (for instance overnight)