"Even if you have all the right conditions, if the baby doesn't stimulate the nipple, you won't have milking," he said.
Pregnancy and the stimulation of nipples may be nature's way of starting lactation, but Jabara notes there are various other conditions that can set off lactation, even in men.
Drugs, fat tissue, tumors, medication, hormone imbalances, and simple nipple stimulation can all lead someone to technically "lactate." Whether it's healthy milk or enough milk to feed a baby is another matter.
Jabara said one possibility could be a tumor in the brain that forces the pituitary gland to produce the hormone prolactin. With the proper nerve stimulation over time, there could be a chance of lactating.
A man simply being overweight could also set the stage for lactating. Jabara said the fat tissue in the body can increase estrogen levels in men, resulting in breast tissue similar to women.
"If you noticed, some obese men have gynecomastia," said Jabara, meaning abnormally large breast tissue and mammary glands for a man.
Enough stimulation with gynecomastia, and a man can start lactating. The same effect can happen for boys or women.
"But a child or a male would not have enough breast tissue to provide all the components of the milk," said Jabara.