The Connection Between Lactation and Postpartum Aggression

It’s lactation — not parenthood — that makes birth parents so aggressive to perceived threats: use these hormones to your advantage

Everyone knows the saying, “don’t come between a mama bear and her cubs”. This is often colloquially used to refer to the ferocity with which human mums will defend their children.
Turns out, it’s not just motherhood — it’s lactation that produces the highest level of aggression from a parent toward a perceived threat.

The hormonal influence of lactation is so profound that it’s considered a more extreme hormonal impact than adolescence or menopause.

I’m a breastfeeding mom of triplets, so breastfeeding has consumed many hours of my day. I’ve been stunned at how intense the impact of breastfeeding hormones has been, and how much it’s influenced my everyday life and my relationships.

Author breastfeeds two of her toddlers. Photo by Caedy Convis Photography.

Whether you’re breastfeeding, have a partner who is, or merely want to understand more about lactation — let’s look at the role of these hormones, and how breastfeeding mothers, and parents in general, can use these primal hormones to our advantage in modern society — where the threats to our babies aren’t obvious toothy tigers, but are more insidious, like still-face syndrome and disrespectful relatives.

A study titled “Maternal Defense: Breast Feeding Increases Aggression by Reducing Stress” shares insights on the connection between aggression and lactation. This study is behind most of the claims stated in this article.

Protection and postpartum aggression

Protecting one’s young is an obvious survival mechanism among animals and humans alike and is integral to the survival of any species who aren’t born fully mature and self-sufficient.

But in many animal species — including primates, rats, lions and cats — when the females are lactating, they are much more aggressive than any other adults toward any perceived threats toward their infants or even their nest.

In “Maternal Defense: Breast Feeding Increases Aggression by Reducing Stress”, the authors observed several intriguing data points:

  1. Mothers who exclusively breastfeed are almost twice as aggressive to perceived threats as a birthing mother who feeds with formula or a non-birthing mother.
  2.  Breastfeeding seems to dampen a mother’s arousal in situations that seem threatening to her baby, enabling them to respond more aggressively. Greater parasympathetic control in the face of stressors combined with a hormonally suppressed physiological arousal encourages the breastfeeding mother’s response to a perceived threat to be “fight”, rather than “flight” or “freeze” (Specifically, breastfeeding hormones lower a mother’s blood pressure, and blood pressure correlates inversely with aggression.)
  3. How much milk is produced directly influences how much aggression occurs. Basically, the more milk a mom makes, the more likely she was to be aggressive, according in the study. I thought this particular portion was fascinating. To me, this means I (as a breastfeeding mom of triplets) am more likely to be aggressive than a mom who is breastfeeding a singleton, as I am producing more milk! And, since my wife and I are both breastfeeding our babies (she carried our singleton and I carried our twins, who were born within weeks of each other), it means that a mom who is exclusively breastfeeding twins or triplets by herself is more likely to be aggressive than me.
Author’s 9mo old babies (left Arden, middle Miko, right Conall) play. Photo from @motownmultiples.

Human babies are the most immature babies on the planet. The time from birth to self-sufficiency is longer than any other mammal or animal. Parents being motivated to keep their helpless baby alive is a vital part of survival. A lactating mother is likely to have her baby nearby, so incentivizing her biologically to protect her baby is in survival’s best interest.

The researchers take care to say that breastfeeding parents aren’t indiscriminately aggressive — they aren’t going around picking fights. They’re exclusively focused on what keeps their baby alive, and so the aggression boost is only in situations that threaten the baby or themselves.


RELATED: Why My Wife and I Decided to Both Get Pregnant at the Same Time For Irish Twins


Dr. Ghada Harsouni, a board certified pediatrician who owns Honeybee Pediatrics and Lactation on the northeast side of Ann Arbor, became a lactation consultant because she realized how hard breastfeeding was and how little she knew, even as a physician. She does lactation consults in her office, as well as takes care of patients in her concierge pediatric practice.

“I find pregnancy and post delivery hormones to be so fascinating!” Harsouni said. “The levels of estrogen and progesterone hormones can impact the level of neurotransmitters in the brain, which help regulate mood. When a mother is pregnant, breastfeeding and postpartum, there are different hormones changing which can also affect mood.”

9 month old photoshoot of Arden (left), Conall (middle), and Miko (right) playing outside. Photo from @motownmultiples.

It’s important to note that the study doesn’t suggest that mothers who aren’t lactating don’t protect their babies — they explicitly note mothers of all types exhibit protective behavior to their young. They also take care to point out that maternal protection can arise in many ways; and lactation is just one of those ways.

Predominantly, the researchers look at lactation as one way that we evolved to provide hormones that help mothers protect their young by dampening a normally prohibitive level of fear in stressful situations.

So this is all very interesting, but what now? After all, needing our fear response suppressed so we can fight off a saber tooth tiger isn’t exactly relevant anymore.

Threats to our babies’ wellbeing are far more insidious these days. They’re a relative that doesn’t care about our family’s boundaries, or the constant temptation to just scroll on our phone instead of gazing into our newborn’s eyes, or the well-meaning but neuroscientifically-disproved advice to leave our babies alone too long when they cry which causes a cascade of cortisol in their vulnerable brains.

Two responses, curiosity and fact-checking, really helped me moderate the mom rage.

Get curious about your emotional (aggressive) response.

If you’re finding yourself getting so angry at your partner for forgetting to wash your pump parts, or your mother-in-law for kissing your baby on the mouth or your dog for barking and waking up the baby — try to get curious about the why behind this emotion. Do you feel like the childcare labor is unbalanced with your partner? Is your mother-in-law disrespecting other boundaries? Are you stressing about your baby’s sleep schedule and view any disruptions as a threat to their wellbeing?

I am so lucky that my babies’ biological dad, T, wants to help with parent duties. He even helps out with night shifts several nights a week. But I would find myself getting so angry at him when one baby (or all!) would wake up screaming and he would sometimes be sleeping through it (how?) until I would literally shake his shoulders to wake him up. I’m talking like, angry. There is no anger quite like watching someone snore while you’re trying to hold two screaming babies as you shout his name to get some help.

Harsouni said, “I want women to know that if they are experiencing changes in their moods, it is not them, it is transient, and there is so much help they can get from our local therapists. I want them to not be afraid to seek out this care. The reason behind my clinic name, Honeybee Pediatrics and Lactation, is because we are a hive. Women have to take care of each other, and that’s what I stand by.”

After curiosity, fact-check.

Once you’ve investigated the why behind your feelings, do some fact-checking.
Do you think your why is a fair response, one you’re happy with? Or did you discover a different underlying problem? And is that something you can address?

7 month birthday photos, St. Paddy’s theme! Conall (left), Arden (middle), Miko (right). Photo by @motownmultiples.

If the childcare labor is unbalanced, initiate a conversation: you deserve support. If your mother-in-law is disrespecting other boundaries of your family, that is a threat to your family’s wellbeing. If you’re overly stressed about your baby’s sleep schedule, perhaps see if becoming more informed about the topic would ease your worries: for example, learning that wake windows are approximate, not set in stone; so it’s entirely normal for your baby’s wake window to vary widely, compared to online schedule suggestions.

If the childcare labor isn’t unbalanced but you’re still so angry at your partner, check your basic needs: eat a snack, drink some water, ask your partner to watch the baby while you lay down for a nap or a rest. It’s so easy to feel dysregulated when our most basic needs aren’t being met. If your mother-in-law is genuinely respectful of your family’s boundaries and this was just a forgetful moment, gently remind her. If the dog barking was just particularly hard today, forgive yourself for yelling at the dog (and maybe give them a treat once you resettle the babe).

My fact checking with T helped reaffirm that it was unreasonable of me to expect him to wake up as easily as I do. People can’t really help how deeply they sleep, and as a breastfeeding mum, I wake up far more easily than a non-breastfeeding parent. I problem-solved with T, telling him the situation and asking for his thoughts. He told me to feel no compunction in waking him up at anytime when he was on shift, and helped problem-solve himself by telling me the loud white noise machine drowned out the noise of the babies and helped him sleep through crying (which is exactly what it was supposed to do…!).
So I turned down the white-noise machine and it definitely helped. And at times when I still felt angry, I fact-checked those feelings (it’s not his fault, this is just my emotions being tired and crabby) and woke him up when I needed him.

I also found fact-checking the incredible impact of these hormones themselves on my mood to be so helpful; to encourage me to give myself grace as well. I wasn’t a failure if I felt overwhelming rage when my babies were screaming. I was merely a new mother, wildly sleep-deprived, and affected by intense lactation hormones that are flooding my brain and nervous system. I wasn’t bad for feeling angry; it was a normal, biological response to a perceived threat to my baby.

Seeking support

“Baby screaming can be so triggering,” Harsouni said. The most important way mothers can tackle the stressors of new parenthood, along with all the hormonal changes to rage, sadness, and more is to find community support.

For the many parents who don’t have a village, Dr. Harsouni recommends to reach out to groups. “There are so many lactation networks ready to help,” she says. “I am currently still researching and making lists of nearby contacts to be able to assist mothers. Lists from therapists, lactation consults, pediatricians and the list goes on to complete our hive.”

If you’re a parent who has breastfed, how did you experience the impact of lactational hormones? If you’re a non-breastfeeding parent, how did you help support your partner (or yourself) during this emotional time?