Diethyltoluamide or DEET is an effective insect repellent against mosquitoes, black flies, ticks and fleas. Since the last update, we have not found published data on its excretion in breast milk. Its pharmacokinetic data (low molecular weight, moderate cutaneous absorption and highly lipophilic) make its transfer to milk possible in amounts that could be significant. There is no evidence that the use of DEET in breastfeeding mothers affects the child (Koren 2003). Avoid the use of products with a concentration higher than 25%, do not use over extended areas of skin (Chen 2009) and do not apply to the chest. Avoid contact with the baby and ventilate well. It is a product which is approved by the American Academy of Pediatrics for use in infants older than two months at concentrations not exceeding 30% (AAP 2017). WHO list of essential medicines: compatible with breastfeeding (WHO / UNICEF, 2002).