Abstract It is universally accepted that human milk is the optimal, exclusive source of nutrition for infants 0 to 6 months of age, and may remain part of the healthy infant diet for the first 2 years of age and beyond. Despite advances in infant formulas, human milk provides a wide range of benefits, due in part to its bioactive matrix that cannot be replicated by any other source of nutrition. When there is an insufficient volume of mother’s milk for the vulnerable newborn, pasteurized donor human milk should be made available, as a bridge to mother’s milk and as the first alternative feeding choice, followed by commercial formula. There is a limited supply of donor milk in Canada and distribution is prioritized for sick, hospitalized neonates. Informal milk sharing is the practice of donating and receiving expressed human milk without going through a human milk bank. Informal milk sharing carries risk for bacterial and viral transmission as well as inconsistency and uncertainty regarding donor screening. Paediatricians and other health care providers need to be aware of the risks of informal milk sharing and be able to counsel families appropriately on safer alternatives.