What are Mammary Glands?

Mary McMahon
Mary McMahon

Mammary glands are specialized glands unique to mammals. Along with several other traits, mammary glands set mammals apart from other members of the animal kingdom. These glands are capable of producing milk, a nutrient-rich substance which is used to nourish baby mammals. Depending on the species and the conditions, milk is produced for varying amounts of time, providing young mammals with the basic nutrition they need to thrive and grow until they are old enough to eat solid foods.

The mammary glands produce milk.
The mammary glands produce milk.

These glands are believed to have arisen from sweat glands. The groundwork for the mammary glands is laid during fetal development, and mammals of all genders are born with rudimentary mammary glands, laid out in pairs along the “milk lines” which run down the abdomen. Mammals such as humans produce only two mammary glands, in contrast with animals such as pigs, with an impressive 18. The difference in number usually reflects the number of young the mammal carries during a typical pregnancy.

Fetal development sets the groundwork for mammary glands.
Fetal development sets the groundwork for mammary glands.

The glands stay relatively underdeveloped until the mammal begins to experience hormone changes which promote the further development of the mammary glands. This generally occurs in female mammals only. During pregnancy, additional hormone changes prepare the glands to actively produce milk, and when the baby is born, the mother can usually express milk very quickly. These milk producing glands work by connecting a series of hollows lined with milk-expressing cells to a system of ducts which drain to the nipple. As the baby develops and loses interest in milk, production will go down, and eventually the mammary glands will stop producing altogether.

It is sometimes possible for male mammals to produce milk from their mammary glands, although this is unusual, and may require the use of hormones to stimulate gland development and milk production. Several factors can influence the quantity and quality of milk produced. Diet is important, with malnourished mammals producing less milk, and diet can also affect the flavor of the milk in some cases. Stress can also be a factor.

Humans have developed a taste for the milk of several fellow mammals, including cows, sheep, and goats. These animals are raised for their milk and are routinely bred and weaned to keep up a consistent supply of milk. A wide variety of products can be made from animal milk, including cheese, butter, yogurt, kefir, and skyr, and many cultures have their own milk specialties, some of which are thousands of years old.

Mammary glands produce all the breast milk a baby needs for the first three months of life.
Mammary glands produce all the breast milk a baby needs for the first three months of life.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@starrynight - Breastfeeding is natural, but I can see why it would make some people uncomfortable if done in public. Women who choose to breastfeed should remove themselves and go somewhere private.

I'm fascinated that some mammals have as many as 18 mammary glands! I assume that corresponds to the amount of babies they have at once. Since humans usually only have babies one at a time, they only need two mammary glands. But an animal like a pig has a lot of piglets all at once, so it stands to reason they would have more mammary glands.


I think it's funny how often people forget that breasts are only really only there to act as a conduit for the mammary glands. It makes me really upset when people act like breast feeding is "dirty" or something.

I've read several news stories about women being asked to leave a public place because they were breastfeeding. I believe the women were covered up with a blanket as well. But the owner of the establishment found breastfeeding so objectionable he asked them to leave anyway.

I find this utterly ridiculous! I know breasts are also considered sexual, but it's not as if these women were performing a sex act in public. They were just breastfeeding!


@dfoster85 - The key word is "preparing." The body isn't really designed for simultaneous nursing and pregnancy, though certainly many women do both successfully. I think it's the progesterone that does it, but you can get more information from the Kellymom website or rom the book "Adventures in Tandem Nursing."

No, there's nothing you can do about it. Because it's a hormonal change, increasing demand (i.e., nursing more often, pumping, etc.) will *not* increase your supply. Because your son is so close to a year, you might ask the pediatrician if he can have whole milk as a supplement. If he takes a bottle, great, if not, time for him to learn about sippy cups! Or he might be satisfied with an increase in his solid foods.

I think you will find that your son will wean naturally as your supply decreases; after the first birthday, when babies start walking, is a sort of window of opportunity for weaning. The benefits of continued breastfeeding are real, but I think having a sibling is even better, so don't beat yourself up if weaning happens!

And congratulations on your new baby!


So if the mammary glands during pregnancy are preparing to produce milk, then why is my milk drying up? My son is eleven months old and still nursing, and I'm eight weeks pregnant with our second. (Lucky me, getting pregnant while I'm still nursing.)

But for me it's becoming increasingly uncomfortable, and I feel like my son is frustrated because he's not getting enough. Why would pregnancy be affecting my milk supply like this? Ist there anything I can do about it? I was hoping to continue nursing my son through most of my pregnancy as I know there are benefits to continued breastfeeding past the first birthday.

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