As embryos, men and women start off, well, more or less as women.
The genetic template of the body follows the path of the X chromosome for approximately
60 days of development, providing the embryonic man with a set of nipples.
More specifically, approximately 4-6 weeks into development, embryos develop parallel
mammary ridges.
These ridges, called milk lines, span between the armpit and chest then descend down each
side to the lower abdomen and finally narrow in towards the groin, ending high on the thigh.
Ultimately these milk lines regress, except for in the chest area (in most cases, more
on this later), leaving us with mammary buds that develop into the familiar pair of cold
weather pokies, some lactating glands called lobules, ducts, a bit of fatty tissue in between,
etc.
For males, the Y chromosome later sets off a cacophony of genetic changes and hormonal
flows, especially one quite near and dear to men aspiring to become Citius, Altius,
and Fortius.
Among other things, the influx of this hormone, testosterone, stimulates the growth of the
penis and testes.
However, this only answers part of the question of “why do men have nipples”.
Another facet of this is why have nipples stuck around in men when evolutionary processes
could have weeded them out?
Quite simply, it’s generally thought nipples are still around in men because they just
don’t matter enough for evolution to rear its head.
Genetic uncoupling of male and female characteristics occurs when said characteristics have substantial
bearing on reproductive success.
Nipples, however, persist, because there’s nothing really to select against them – they
simply don’t do much either way!
As “nippled breasts never lost a fair maiden” and because nipples are there before testosterone
kicks in, they’re seemingly here to stay.
However, it would be a technical faux pas to lump the male nipple in with the other
vestigial structures – indeed, the male nipple is entirely ready to perform its original
function, leading to male lactation.
Yes, you heard that right- men can breastfeed babies if they really want to and it’s not
even that hard to make it happen.
So what’s going on here?
Milk is produced in small hollow cavities in breast tissue called alveoli, where the
linings contain cells that secrete milk when properly triggered.
While there are a variety of things that go into someone lactating, including various
hormones, the main trigger for milk production is sufficient amounts of the hormone prolactin,
which is primarily produced by the pituitary gland, though also by the prostate in men
and a layer of the uterine wall known as the myometrium in women, among other places.
Both men and women have alveoli, but typically have markedly different levels of prolactin.
In fact, a normal non-pregnant woman has around one third to twice the hormone than the average
man at any given time.
Late in a pregnancy and after giving birth, prolactin levels can peak as high as ten times
more in these women compared to what you'll typically find in males.
So how can men lactate without the necessary processes involved in child birth triggering
a ramp up of prolactin production?
Prolactin is ultimately metabolized by the liver helping to regulate its concentration
in the body in conjunction with certain mechanisms in the hypothalamus.
When the liver isn't functioning properly, abnormally high levels of certain hormones
may build up.
This is what is thought to have happened to hundreds of male POWs during WWII, who, after
suffering months of starvation, began lactating during their recovery; experts opine that
the stress and deprivation interfered with the liver and certain hormone producing glands'
normal activities.
Once properly fed, the liver took longer to recover than the hormone producing glands-
pertinent to the topic at hand resulting in a build-up of concentration of prolactin in
the POWs' bodies, causing them to start lactating.
More recently a report in the Canadian Medical Association Journal documented a case of a
man who had a pituitary tumor that resulted in, among other things, overproduction of
prolactin, causing him to lactate.
In fact, there are numerous reports throughout history of men lactating, including in The
Talmud, where a poor man whose wife died while their baby was quite young had "a miracle
. . . his breasts opened and he nursed his child."
In Numbers 11:12 in the Bible, (whether claiming it was a known literal occurrence or not isn't
clear) it notes, "Have I conceived all this people?
Have I begotten them, that thou shouldest say unto me, Carry them in thy bosom, as a
nursing father beareth the sucking child, unto the land which thou swarest unto their
fathers?"
In Anomalies and Curiosities of Medicine (1896), Gould & Pyle report that both a male South
American native and male Brazilian missionaries nursed children after their wives lost the
ability.
And a similar much more modern and well documented report was made in 2002 of a Sri Lankan man,
Mr. B Wijeratne, who took up breastfeeding his 18 month old daughter after his wife died
giving birth to their second child.
He initially had attempted to feed the older child formula upon her mother's death, but
this was summarily rejected by the toddler.
He later stated, "unable to see her cry, I offered my breast.
That's when I discovered that I could breastfeed her."
If you're wondering how this is possible, it's known that expectant fathers and those
with newborns also see a spike in prolactin compared to their normal levels.
While not anywhere close to enough to cause lactation in men normally, you may be aware
that nipple suckling can result in women who didn't just have a baby ultimately lactating
anyway.
What's less well-known is that the receptors responsible for triggering the brain to in
turn stimulate the pituitary gland to produce more prolactin and trigger the release of
oxytocin, which is necessary to get the milk flowing, exist and function in both men and
women.
This process can commonly be observed in cases of women adopting babies and wanting to breastfeed
them.
They are able to achieve this via regularly having the child suckle and further using
a breast pump every few hours over the course of several weeks.
According to the Goldfarb Breastfeeding Clinic, in a small study they conducted looking at
228 women attempting this, 31% were able to produce enough milk to provide the full caloric
and nutritional needs of the baby.
While that may seem a small percentage, it should be noted that nearly all 228 women
were at least able to provide some milk to their adopted babies.
This same thing can also be observed in various animals, including sometimes used to cause
goats who have never had kids to produce milk.
For men, as with women, the net result of having a baby around and regularly using a
breast pump / letting said baby suckle results in a prolactin spike.
For some men, this may be high enough to trigger milk production, allowing the male to breastfeed
a baby.
(Whether that's what happened in the case of the Sri Lankan man or if he had some other
condition isn't clear, with his physician, Dr. Kamal Jayasinghe, simply noting to the
media, "Men with hyperactive prolactin hormone can produce breast milk.")
There are also some drugs that occasionally have the side effect of increased prolactin
concentration in the body sufficient to cause male lactation, such as the antipsychotic
chlorpromazine (marketed under the name Thorazine and Largactil) and the heart medication digoxin
(marketed under the name Lanoxin, among other names).
It should also be noted here that some teenage and adult men produce milk without babies
or drugs.
Called male galactorrhea, it often develops during the hormone surge of puberty, but can
also be caused by hypothyroidism, among other conditions.
Videos documenting such lactation, such as Bodybuilder Chest Milk, abound on the web.
In addition, approximately 5% of newborn babies of both sexes secrete milk from their breasts.
Colloquially called Witch's milk, it is believed to be caused by the combined effects of prolactin
and growth hormones from the mother's milk, along with thyroid and pituitary hormones
from the baby.
The milk produced is similar in composition to a typical woman's milk.
The condition usually subsides within a couple of months.
Finally, as I'm sure there are some men out there interested despite the social stigma
(and potentially some women who'd kill for their men to be able to help out on the breastfeeding
front), outside of the aforementioned nipple suckling technique boosting natural prolactin
levels, a more effective solution for men would be to simply buy some prolactin and
introduce it into the body directly.
However, while this is sometimes done to induce lactation in animals, and we were able to
locate some sources of human prolactin for sale online, at least as far as we can find,
it doesn't appear to be a treatment any doctor we could find will administer and oversee
for human males wanting to breastfeed their children, and potential side effects of sustained
high levels of prolactin in males doesn't appear to be something well studied.
However, it is known that abnormally high prolactin levels can cause a loss of libido
in men and women, and in men potential problems with impotence while said levels remain high.
Further, prolactin is involved in at least 300 known processes in the body, including
playing a role in one's metabolism and immune system, and in men potentially lowering testosterone
levels.
It should also be noted that the general consensus is that, due to certain physiological processes
during puberty, even with sufficient prolactin it is unlikely a breastfeeding father would
produce nearly as much milk as a woman with equivalent levels.
That said, while that seems to be the general consensus of the medical community, we couldn't
find a single study looking at volume of milk production in lactating males that have been
studied, so it’s possible this is just a widely accepted hypothesis at this stage.
And if you're wondering about the nutritional value of human male breast milk compared to
female breast milk, in a 1981 study of a lactating human male, it was determined that, much like
the milk found in both male and female lactating babies, to quote the study "The concentrations
of lactose, proteins, and electrolytes in the breast secretion of this man are within
the range of colostrum and milk obtained from normal lactating women."
Bonus Fact: Ever wonder how some people end up with more
than two nipples?
Well, wonder no more- In short, this is just a result of an incomplete regression of the
milk line that results in one or more extra mammary buds developing outside of where we'd
normally expect them, but still usually along the milk line.
The end result is an extra nipple, and sometimes associated breast tissue.
These are surprisingly common, appearing on as many as 1 in 20 people, though most who
have them don't recognize the often tiny protuberance as an extra nipple.
Numbering among the supernumerary are reportedly Mark Wahlberg, Lilly Allen, Harry Styles and
Tilda Swinton.