The phenomenon of male lactation in humans has become more common in recent years due to the use of medications that stimulate a human male's mammary glands. It is commonplace knowledge that human males have nipples. It is not so often understood that they also have mammary glands. Ordinarily the mammary tissue is low in volume and cannot be noticed. Nevertheless, men can suffer from breast cancer. Under the appropriate hormonal stimulus, the hormonal stimulus that nature provides to human females when they become pregnant and give birth, the mammary glands of human males can also produce milk. The volume of milk produced will be small relative to the amount that a female can produce. The most common circumstance under which lactation is induced is when hormonal treatments are given to men suffering from prostate cancer. Female hormones are used to retard the production of cancerous prostate cancer, but the same hormones also stimulate the mammary glands.
The phenomenon of male lactation occurs in some non-human species, and the lactating males may assist in the nursing of their infants. One species of fruit bat (Dyacopterus spadiceus) is notable for this reason. According to CBC Radio, spontaneous lactation and even nursing has occasionally been observed in humans.