Why do men have nipples? Almost everyone has nipples, regardless of whether they’re a man or a woman, transgender or cisgender, a person with large breasts or a flat chest. But nipples seem to make a lot more sense on people with the ability to breastfeed, right? It’s obvious the nipples we think of as “female nipples” — like the nipples cisgender women have — are meant to serve a purpose. But what about male nipples? Those are the ones that cisgender men usually have. The answer, for the most part, is fairly simple. Men have nipples because nipples develop in the womb before embryos become distinctly male or female. So by the time a Y chromosome kicks in to distinguish a fetus as male, the nipples have already secured their place.

Wait, so everyone technically started as female in the womb? Some people think of it this way: Everyone starts out as female in their early development in utero. From this understanding, a man’s nipples would seem to be left over from when he was initially female. Here’s another way to think of it: Everyone starts out as gender neutral. A few weeks in, the Y chromosome starts creating changes that lead to the development of testes in males. Female fetuses go through changes that will eventually lead to the development of breasts. Our development is different at this point and also during puberty, when secondary sex characteristics like pubic hair form.

Why hasn’t evolution selected against this trait? If a trait isn’t necessary to our survival, evolution eventually eliminates it. And if males aren’t designed to breastfeed babies, then does that mean their nipples aren’t necessary? Well, this isn’t entirely accurate. The truth is, we have plenty of nonessential traits, like wisdom teeth, that are just left over from our development as a species. Such traits are called vestigial, meaning we still have them because they’re not a priority for evolution to select against. It’s not like male nipples are hurting anyone, so it’s no big deal for evolution to simply leave them be. But there’s another layer to this, too: Even though they’re not used for breastfeeding, male nipples are actually more useful than you might think.

So, there’s a point to having nipples? Describing male nipples as left over from fetal development makes them sound pretty useless, doesn’t it? Are male nipples kind of just… there? Actually, male nipples still serve a purpose as an erogenous zone. Just like female nipples, they’re sensitive to touch and can come in handy for erotic stimulation. Hello, nipple orgasms! One study found that nipple stimulation enhanced sexual arousal in 52 percent of men.

What about lactation (galactorrhea)? While it’s true that male nipples aren’t ordinarily used for breastfeeding, lactation is possible. For transgender men, possible steps for physical transition can include surgery, taking hormones, or nothing at all. So, depending on the physical and hormonal changes that have taken place, lactation can happen just like it does for cisgender women. But even cisgender men can lactate if a particular hormone, called prolactin, takes effect. It’s a condition known as male galactorrhea. It’s usually the result of: medication

malnutrition

a health condition like an overactive thyroid

Can males develop breast cancer? Males can develop breast cancer, though it’s rare. It accounts for less than 1 percent of all breast cancer cases. This can happen at any age, but just like women, men are more likely to develop breast cancer as they get older. However, most men aren’t getting regular mammograms or reminders to check for lumps in the shower, like women often do. This means they’re also more likely to miss the signs of breast cancer. If you’re a man, look out for symptoms like: a lump in one breast

discharge or redness around the nipple

discharge from the nipple

swollen lymph nodes under your arm If you begin experiencing these or other unusual symptoms, see a doctor or other healthcare provider.

But males don’t have breasts? We tend to think of breasts as a woman’s trait, so you may be surprised to know boobs are actually gender neutral. The only difference between the breasts we think of as “male” and “female” is the amount of breast tissue. Typically, the hormones that kick in during puberty cause girls’ breasts to grow, while boys’ breasts stay flat.

Are there any other conditions to watch for? Not every cisgender man will end up with flat breasts. For some, a condition called gynecomastia can lead to the development of larger male breasts. It’s usually the result of a hormone imbalance, such as low testosterone levels. Other conditions to watch out for include: Mastitis. This is an infection of the breast tissue. It typically shows up as breast pain, swelling, and redness.

This is an infection of the breast tissue. It typically shows up as breast pain, swelling, and redness. Cysts. These are fluid-filled sacs that can develop in the breast.

These are fluid-filled sacs that can develop in the breast. Fibroadenoma. This noncancerous tumor can form in the breast. These are all more common in female breasts, but they’re not unheard of among males. Talk to a doctor about any unusual inflammation, pain, or lumps.

Are there any other differences between a ‘male’ and a ‘female’ nipple? At the end of the day, there are a whole lot of parallels between the nipples we think of as “male” and “female.” They start out the same in the womb and remain similar until puberty. Even after puberty creates a difference in breast sizing, breast tissue still exists in everyone, boys and girls included. Sure, if you asked Tumblr or Instagram, they’d tell you that “female” nipples are more explicit than “male” ones. But somebody should tell them to check out what science has to say, because when you get down to the details, that distinction makes little sense.