Anatomy

The male breast structure is rudimentary.

Under the nipple and the areola – the colored circle around the nipple- there are only some very rudimentary mammary ducts.

These ducts are thin tubes that in women carry milk to the nipple.

For that reason female ducts develop little glands at extremities – the lobules that produce milk during pregnancy – under the influence of the hormones in the blood.

In men, the hormones produced in the testicles have the opposite effect – they prevent the mammary tissue from developing. 

When a boy enters puberty, he does not produce the hormones that promote breast development, but instead the male hormones that restrict it. This is believed to be the reason why breast cancer is much more rare among men that women.

Few if any breast lobules develop in men