Cow's milk allergy is rare in exclusively breastfed infants. To support the continuation of breastfeeding an infant after diagnosis with a cow's milk allergy, it is critical to examine the evidence for and against any form of cow's milk elimination diet for lactating mothers. In this narrative review, we highlight the lack of high-quality evidence, hence subsequent controversy, regarding whether the minuscule quantities of cow's milk proteins detectable in human milk cause infant cow's milk allergy symptoms. Current clinical practice recommendations advise a 2–4 week trial of maternal cow's milk dietary elimination for: a) IgE-mediated cow's milk allergy only if the infant is symptomatic on breastfeeding alone; b) non-IgE-mediated associated symptoms only if the history and examination strongly suggest cow's milk allergy; and c) infants with moderate to severe eczema/atopic dermatitis, unresponsive to topical steroids and sensitized to cow's milk protein. There should be a clear plan for home reintroduction of cow's milk into the maternal diet for a period of 1 week to determine that the cow's milk elimination is responsible for resolution of symptoms, and then subsequent reoccurrence of infant symptoms upon maternal cow's milk reintroduction. The evidence base to support the use of maternal cow's milk avoidance for the treatment of a breastfed infant with cow's milk allergy is of limited strength due to a lack of high-quality, adequately powered, randomised controlled trials. It is important to consider the consequences of maternal cow's milk avoidance on reducing immune enhancing factors in breast milk, as well as the potential nutritional and quality of life impacts on the mother. Referral to a dietitian is advised for dietary education, along with calcium and vitamin D supplementation according to local recommendations, and a maternal substitute milk should be advised. However, for most breastfed infants with cow's milk allergy maternal cow's milk dietary elimination will not be required, and active support of the mother to continue breastfeeding is essential.