Cosleeping and Biological Imperatives: Why Human Babies Do Not and Should Not Sleep Alone

By James J. McKenna Ph.D.
Edmund P. Joyce C.S.C. Chair in Anthropology

Mother-Baby Behavioral Sleep Laboratory
University of Notre Dame

Where a baby sleeps is not as simple as current medical discourse and recommendations against cosleeping in some western societies want it to be. And there is good reason why. I write here to explain why the pediatric recommendations on forms of cosleeping such as bedsharing will and should remain mixed. I will also address why the majority of new parents practice intermittent bedsharing despite governmental and medical warnings against it.

Definitions are important here. The term cosleeping refers to any situation in which a committed adult caregiver, usually the mother, sleeps within close enough proximity to her infant so that each, the mother and infant, can respond to each other’s sensory signals and cues. Room sharing is a form of cosleeping, always considered safe and always considered protective. But it is not the room itself that it is protective. It is what goes on between the mother (or father) and the infant that is. Medical authorities seem to forget this fact. This form of cosleeping is not controversial and is recommended by all.
Unfortunately, the terms cosleeping, bedsharing and a well-known dangerous form of cosleeping, couch or sofa cosleeping, are mostly used interchangeably by medical authorities, even though these terms need to be kept separate. It is absolutely wrong to say, for example, that “cosleeping is dangerous” when roomsharing is a form of cosleeping and this form of cosleeping (as at least three epidemiological studies show) reduce an infant’s chances of dying by one half.

Bedsharing is another form of cosleeping which can be made either safe or unsafe, but it is not intrinsically one nor the other. Couch or sofa cosleeping is, however, intrinsically dangerous as babies can and do all too easily get pushed against the back of the couch by the adult, or flipped face down in the pillows, to suffocate.

Often news stories talk about “another baby dying while cosleeping” but they fail to distinguish between what type of cosleeping was involved and, worse, what specific dangerous factor might have actually been responsible for the baby dying. A specific example is whether the infant was sleeping prone next to their parent, which is an independent risk factor for death regardless of where the infant was sleeping. Such reports inappropriately suggest that all types of cosleeping are the same, dangerous, and all the practices around cosleeping carry the same high risks, and that no cosleeping environment can be made safe.

Nothing can be further from the truth. This is akin to suggesting that because some parents drive drunk with their infants in their cars, unstrapped into car seats, and because some of these babies die in car accidents that nobody can drive with babies in their cars because obviously car transportation for infants is fatal. You see the point.

One of the most important reasons why bedsharing occurs, and the reason why simple declarations against it will not eradicate it, is because sleeping next to one’s baby is biologically appropriate, unlike placing infants prone to sleep or putting an infant in a room to sleep by itself. This is particularly so when bedsharing is associated with breast feeding.
When done safely, mother-infant cosleeping saves infants lives and contributes to infant and maternal health and well being. Merely having an infant sleeping in a room with a committed adult caregiver (cosleeping) reduces the chances of an infant dying from SIDS or from an accident by one half!


In Japan where co-sleeping and breastfeeding (in the absence of maternal smoking) is the cultural norm, rates of the sudden infant death syndrome are the lowest in the world. For breastfeeding mothers, bedsharing makes breastfeeding much easier to manage and practically doubles the amount of breastfeeding sessions while permitting both mothers and infants to spend more time asleep. The increased exposure to mother’s antibodies which comes with more frequent nighttime breastfeeding can potentially, per any given infant, reduce infant illness. And because co-sleeping in the form of bedsharing makes breastfeeding easier for mothers, it encourages them to breastfeed for a greater number of months, according to Dr. Helen Ball’s studies at the University of Durham, therein potentially reducing the mothers chances of breast cancer. Indeed, the benefits of cosleeping helps explain why simply telling parents never to sleep with baby is like suggesting that nobody should eat fats and sugars since excessive fats and sugars lead to obesity and/or death from heart disease, diabetes or cancer. Obviously, there’s a whole lot more to the story.

As regards bedsharing, an expanded version of its function and effects on the infant’s biology helps us to understand not only why the bedsharing debate refuses to go away, but why the overwhelming majority of parents in the United States (over 50% according to the most recent national survey) now sleep in bed for part or all of the night with their babies.

That the highest rates of bedsharing worldwide occur alongside the lowest rates of infant mortality, including Sudden Infant Death Syndrome (SIDS) rates, is a point worth returning to. It is an important beginning point for understanding the complexities involved in explaining why outcomes related to bedsharing (recall, one of many types of cosleeping) vary between being protective for some populations and dangerous for others. It suggests that whether or not babies should bedshare and what the outcome will be may depend on who is involved, under what condition it occurs, how it is practiced, and the quality of the relationship brought to the bed to share. This is not the answer some medical authorities are looking for, but it certainly resonates with parents, and it is substantiated by scores of studies.

Understanding Recommendations

Recently, the American Academy of Pediatrics (AAP) SIDS Sub-Committee for whom I served (ad hoc) as an expert panel member recommended that babies should sleep close to their mothers in the same room but not in the same bed. While I celebrated this historic roomsharing recommendation, I disagreed with and worry about the ramifications of the unqualified recommendation against any and all bedsharing. Further, I worry about the message being given unfairly (if not immorally) to mothers; that is, no matter who you are, or what you do, your sleeping body is no more than an inert potential lethal weapon against which neither you nor your infant has any control. If this were true, none of us humans would be here today to have this discussion because the only reason why we survived is because our ancestral mothers slept alongside us and breastfed us through the night!

I am not alone in thinking this way. The Academy of Breast Feeding Medicine, the USA Breast Feeding Committee, the Breast Feeding section of the American Academy of Pediatrics, La Leche League International, UNICEF and WHO are all prestigious organizations who support bedsharing and which use the best and latest scientific information on what makes mothers and babies safe and healthy. Clearly, there is no scientific consensus.

What we do agree on, however, is what specific “factors” increase the chances of SIDS in a bedsharing environment, and what kinds of circumstances increase the chances of suffocation either from someone in the bed or from the bed furniture itself. For example, adults should not bedshare if inebriated or if desensitized by drugs, or overly exhausted, and other toddlers or children should never be in a bed with an infant. Moreover, since having smoked during a pregnancy diminishes the capacities of infants to arouse to protect their breathing, smoking mothers should have their infants sleep alongside them on a different surface but not in the same bed.

My own physiological studies suggest that breastfeeding mother-infant pairs exhibit increased sensitivities and responses to each other while sleeping, and those sensitivities offers the infant protection from overlay. However, if bottle feeding, infants should lie alongside the mother in a crib or bassinet, but not in the same bed. Prone or stomach sleeping especially on soft mattresses is always dangerous for infants and so is covering their heads with blankets, or laying them near or on top of pillows. Light blanketing is always best as is attention to any spaces or gaps in bed furniture which needs to be fixed as babies can slip into these spaces and quickly to become wedged and asphyxiate. My recommendation is, if routinely bedsharing, to strip the bed apart from its frame, pulling the mattress and box springs to the center of the room, therein avoiding dangerous spaces or gaps into which babies can slip to be injured or die.

But, again, disagreement remains over how best to use this information. Certain medical groups, including some members of the American Academy of Pediatrics (though not necessarily the majority), argue that bedsharing should be eliminated altogether. Others, myself included, prefer to support the practice when it can be done safely amongst breastfeeding mothers. Some professionals believe that it can never be made safe but there is no evidence that this is true.

More importantly, parents just don’t believe it! Making sure that parents are in a position to make informed choices therein reflecting their own infant’s needs, family goals, and nurturing and infant care preferences seems to me to be fundamental.

Our Biological Imperatives

My support of bedsharing when practiced safely stems from my research knowledge of how and why it occurs, what it means to mothers, and how it functions biologically. Like human taste buds which reward us for eating what’s overwhelmingly critical for survival i.e. fats and sugars, a consideration of human infant and parental biology and psychology reveal the existence of powerful physiological and social factors that promote maternal motivations to cosleep and explain parental needs to touch and sleep close to baby.

The low calorie composition of human breast milk (exquisitely adjusted for the human infants’ undeveloped gut) requires frequent nighttime feeds, and, hence, helps explain how and why a cultural shift toward increased cosleeping behavior is underway. Approximately 73% of US mothers leave the hospital breast feeding and even amongst mothers who never intended to bedshare soon discover how much easier breast feeding is and how much more satisfied they feel with baby sleeping alongside often in their bed.

But it’s not just breastfeeding that promotes bedsharing. Infants usually have something to say about it too! And for some reason they remain unimpressed with declarations as to how dangerous sleeping next to mother can be. Instead, irrepressible (ancient) neurologically-based infant responses to maternal smells, movements and touch altogether reduce infant crying while positively regulating infant breathing, body temperature, absorption of calories, stress hormone levels, immune status, and oxygenation. In short, and as mentioned above, cosleeping (whether on the same surface or not) facilitates positive clinical changes including more infant sleep and seems to make, well, babies happy. In other words, unless practiced dangerously, sleeping next to mother is good for infants. The reason why it occurs is because… it is supposed to.

Recall that despite dramatic cultural and technological changes in the industrialized west, human infants are still born the most neurologically immature primate of all, with only 25% of their brain volume. This represents a uniquely human characteristic that could only develop biologically (indeed, is only possible) alongside mother’s continuous contact and proximity—as mothers body proves still to be the only environment to which the infant is truly adapted, for which even modern western technology has yet to produce a substitute.

Even here in whatever-city-USA, nothing a baby can or cannot do makes sense except in light of the mother’s body, a biological reality apparently dismissed by those that argue against any and all bedsharing and what they call cosleeping, but which likely explains why most crib-using parents at some point feel the need to bring their babies to bed with them —findings that our mother-baby sleep laboratory here at Notre Dame has helped document scientifically. Given a choice, it seems human babies strongly prefer their mother’s body to solitary contact with inert cotton-lined mattresses. In turn, mothers seem to notice and succumb to their infant’s preferences.

There is no doubt that bedsharing should be avoided in particular circumstances and can be practiced dangerously. While each single bedsharing death is tragic, such deaths are no more indictments about any and all bedsharing than are the three hundred thousand plus deaths or more of babies in cribs an indictment that crib sleeping is deadly and should be eliminated. Just as unsafe cribs and unsafe ways to use cribs can be eliminated so, too, can parents be educated to minimize bedsharing risks.

Moving Beyond Judgments to Understanding

We still do not know what causes SIDS. But fortunately the primary factors that increase risk are now widely known i.e. placing an infant prone (face down) for sleep, using soft mattresses, maternal smoking, overwrapping babies or blocking air movement around their faces. In combination with bedsharing, where more vital normal defensive infant responses and may be more important to an infant (like the ability to arouse to bat a blanket which momentarily falls to cover the infants face when its parent moves or turns) these risks become exaggerated especially amongst unhealthy infants. When infants die in these obviously unsafe conditions, it is here where social biases and the sheer levels of ignorance associated with actually explaining the death become apparent. A death itself in a bedsharing environment does not automatically suggest, as many legal and medical authorities assert, that it was the bedsharing, or worse, suffocation that killed the infant. Infants in bedsharirng environments, like babies in cribs, can still die of SIDS.

It is a shame and certainly inappropriate that, for example, the head pathologists of the state of Indiana recommends that other pathologists assume SIDS as a likely cause of death when babies die in cribs but to assume asphyxiation if a baby dies in an adult bed or has a history of “cosleeping”. By assuming before any facts are known from the pathologist’s death scene and toxicological report that any bedsharing baby was a victim of an accidental suffocation rather than from some congenital or natural cause, including SIDS unrelated to bedsharing, medical authorities not only commit a form of scientific fraud but they victimize the doomed infant’s parents for a third time. The first occurs when their baby dies, the second occurs when health professionals interviewed for news stories (which commonly occurs) imply that when a baby dies in a bed with an adult it must be due to suffocation (or a SIDS induced by bedsharing). The third time the parents are victimized is when still without any evidence medical or police authorities suggest that their baby’s death was “preventable,” that their baby would still be alive if only the parents had not bedshared. This conclusion is based not on the facts of the tragedy but on unfair and fallacious stereotypes about bedsharing.

Indeed, no legitimate SIDS researcher nor forensic pathologist should render a judgment that a baby was suffocated without an extensive toxiological report and death scene investigation including information from the mother concerning what her thoughts are on what might or could have happened.

Whether involving cribs or adult beds, risky sleep practices leading to infant deaths are more likely to occur when parents lack access to safety information, or if they are judged to be irresponsible should they choose to follow their own and their infants’ biological predilections to bedshare, or if public health messages are held back on brochures and replaced by simplistic and inappropriate warnings saying “just never do it.” Such recommendations misrepresent the true function and biological significance of the behaviors, and the critical extent to which dangerous practices can be modified, and they dismiss the valid reasons why people engage in the behavior in the first place.

More Information:
Sleeping With Your Baby: A Parent’s Guide To Cosleeping by James J.McKenna (2007). Platypus Press. *BOOK*

McKenna, J., Ball H., Gettler L., Mother-infant Cosleeping, Breastfeeding and SIDS: What Biological Anthropologists Have Learned About Normal Infant Sleep and Pediatric Sleep Medicine. Yearbook of Physical Anthropology 50:133-161 (2007) *FOR FULL PDF OF THIS SCHOLARLY ARTICLE LEAVE COMMENT OR SEND REQUEST TO PEACEFUL PARENTING BLOG AUTHOR*

McKenna, J., McDade, T., Why Babies Should Never Sleep Alone: A Review of the Co-Sleeping Controversy in Relation to SIDS, Bedsharing and Breastfeeding. Paediatric Respiratory Reviews 6:134-152 (2005) *DOWNLOADABLE PDF*



  1. A wonderfully informative & concise piece of work!
    Nature knows best!

  2. Thank you for this! Only a mother would understand why sleeping with her baby, and breastfeeding, is the way to go. If a mother prefers to sleep in bed with her baby then she should be educated about the right ways of doing so. Not condemned.

  3. In the wilderness a baby would die from being eaten by a wolf or swallowed by a python if his mother weren't there to protect him. Just because we have cribs and bedrooms doesn't mean the primal instinct of every newborn to be in constant contact with their mother/protector is any less strong. If someone says my baby cries if I lay him down I say, "well then you have a smart baby." Babies need to be close to their mothers, their sole source of protection and milk or they do not sleep as soundly, bottom line, neither do breastfeeding mothers whose instincts to be within arms reach of their baby is just as strong. There are serious biological factors we mess with if we separate mother and baby even for a short time, physiological and psychological ones!

  4. I bedshare and smoke against all recommendations from everyone... I did it with my first 2 boys and now with my baby girl... 4 times I have woke up(one of the times she was in her crib, where she starts her nights off) to find her NOT BREATHING, the time that she was in her crib she was turning blue in her face, the 3 times she was in my bed I woke up before it got to that point and I sat her up and got her breathing regular... I have been told I should not do it, but I am afraid if I did not, what could have happened to her? I think more studies should be done on mothers who smoke and bedshare(while breast feeding) because in my personal experience I believe her being in my bed SAVED her, not harmed her... I did not know that me smoking when I was pregnant could cause problems for babys breathing, no one ever told me, all the doctors said is I should quit but if I can not it will be ok... NO ONE said she might stop breathing at night:( so now that the harm is done due to me smoking while pregnant, what could I do?

  5. ok, to add on to my last comment... I have found numerous studies saying mothers who smoke should not bedshare, but what I want to see in the studies is, if it is actually safer for a baby(of a smoking mom) to sleep in a crib instead? I think that most people who come to this site can agree that it is safer for a baby to sleep with momma, but what if the momma smoked while pregnant and after wards? would my baby be better off in a crib(where she has turned blue in the face from not breathing) or to be next to me(where I wake up easier to her ques) in other words how many babys whos momma smoked have died of crib death or sids as compared to babys dying while sleeping next to momma who has smoked... sure I can see that it is best to not smoke at all, but unfortunately it is too late now to change that... but I can not see how placing her in a crib for the entire night alone would prevent her from problems... I know myself, and I know that I wake up before my baby does, I have even turned at night and opened my eyes and seen my baby doing the exact same movement as I am doing... just because I smoked it does not mean I am less in tune with my baby, I can not see how her sleeping in a crib would help prevent issues...

  6. I just don't get what being a smoking Mom has anything to do with a breastfeeding and bedsharing Mom?? It's not as if you are smoking in bed let alone around the baby? I'm so confused!

    1. even if you don't smoke in the house and you share a bed with ur child or even just hold him/her during the day, the smoke inur cloths is worse then even 2nd hand smoke. I smoke and my child sleeps with me. I just make sure I dnt smoke after I put on my pjs for bed. that's why they say not to smoke with kids cause even though u dnt smoke around them its still on ur cloths and its the worst. that's just what they say, but I dnt take the chance

    2. Toxins that impact developing/fragile lungs are exhaled from a smoker even during non-smoking times. As a result, the impact of second hand smoking lasts long after a cigarette is extinguished.

  7. Smokers continue to exhale smoke particles (like second hand smoke) even hours after their last cigarette. So even if you're not smoking around your baby, you still exhale smoke around her later. Babies lungs are so young hat it affects them a lot more than it does an adult. If your baby is near you all night, it's like she's inhaling second hand smoke all night. The best thing you can do for her, you, and all your kids is to work on quitting. Kids whose parents smoke are more likely to do it themselves (I was one of those kids), so if you want to help them avoid starting later, work on stopping now. It's hard, but it's so worth it!

  8. @Anonymous - First, I understand - I was a smoking, breastfeeding, bed-sharing mother, too. Here's the deal.

    Secondhand and thirdhand smoke (the kind in your hair, on your clothes) can still affect your little one's respiratory system. It can still lead to asthma and increased sleep apnea.

    Therefore . . . when I was smoking and we were bedsharing, I took precautions. I smoked outside, wore a smock out there that was removed and left outside before I went in the house, and I would shower before laying down with her to go to sleep at night.

    Now that I've said that, I've just got to question one thing you said. You said that no one ever told you smoking while pregnant would cause a problem with your little one's breathing, but it says clearly on the side of the cigarettes that smoking while pregnant can cause complications. I'm not sure what complications you expected . . . but there are several to choose from.

  9. Second hand smoke increases the risk for SIDS, breathing problems (including asthma, sleep apnea, bronchitis, etc), heart problems, ear infections/hearing loss, and tons of other health issues. Even if someone were to smoke outside, the smoke that lingers upon a body/hair/clothes still offers this increased risk. These are reasons why smokers are encouraged to quit and discouraged from co-sleeping.

  10. Thank you for this informative article. I am a registered nurse in a pediatric hospital. I would be grateful if you could send me any pertinent PDF files of scholarly articles on this subject. I will use them to advocate for more mother-baby-friendly co-sleeping arrangements in my hospital.
    Helen Baker

  11. Dr. McKenna was my anthropology professor at Notre Dame. So glad I learned this information early! I now have two boys (3 years and 10 months), who bedshare(d) and breadtfeed. Love the article and must share that our pediatrician is highly regarded in Austin, TX where we live and served on a board for accidental infant deaths. She is opposed to bedsharing. We always got a mini lecture from her on the dangers of bedsharing during well checks for our first born. We still continue to bedshare because we believe it's the best thing for our babies. I think I'll take her this article next time we go in.

  12. This is important to have bed sharing with your newborn child or until 3 to 4 years old. In this way your child feels the love of their mother. Make your your beds are perfect for children so they would safe while sleeping.

    kids beds

  13. So how much napping without parents is okay to obtain the lower stress hormone levels? And co-sleeping for all 5 years is needed for calm adults? Is simply responding to cries quickly before the baby is fully awake enough? Adults tend to say up later than children and may not always nap with them, so cribs and safer sleep areas are helpful for part of each night.

  14. This is awesome! I'm also an RN. Will definitely use this!

  15. I remember being told to not co-sleep with my first baby. That advice didn't even last the first night in hospital with her, because I'd had an emergency C-Section and so there was no way for me to get up and see to Bub easily. So, after the first nurse call for assistance, I told the actually-pretty-on-to-it nurse that it seemed silly to keep Bub in a cot next to the bed, when she could just sleep next to me, and I wouldn't need to call for help each time I needed to feed her. The nurse went "Actually, I agreed with you. Stuff hospital policy, do what you need to", and left me to it. Bub continued to spend a couple of hours next to me every night until she was 6 months old, though she is our little Miss Independent, and often actually preferred going to sleep in her own space. Even now however at ten she still sometimes asks to sleep next to me, especially if she's going through a rough time. Clearly there is something to being close to Mum that helps her feel protected and secure while she sleeps.

    Second Bub - really didn't have a choice about bed-sharing. From day one she had to sleep next to me - she couldn't handle being physically apart from me. If I put her down, even for just a moment, she'd scream. And forget putting her down for naps or night sleeps. If she couldn't touch me, she cried. Her Dad didn't agree with me bed-sharing, partly because AGAIN we were told NOT to bed-share, but probably mostly because he felt it limited his chances of 'getting any'. However, no sleep for any of us showed him the wisdom of my motherly instincts. Bub slept next to me from then on solidly until she was 6 months, when she finally started being able to have her own space.

    I remember being told by so-called experts that I was going to have issues with her if I kept 'giving in to her demands', that I was encouraging the 'clinging behaviour, and I was setting her up for serious emotional issues later on'. Eight years later? She is the most amazingly independent confident girl. She's outgoing, bright, happy, and basically just adds sunshine to the lives of everyone around her. And emotionally, she's the most resilient child I've ever met. She just naturally has this ability to shrug off what ever life throws at her. Personally, I think she's this way BECAUSE I 'gave in' and gave her the physical contact she needed early on. It was extremely draining for those first months, but imagine how much worse it would have been if I'd listened to the expert advice on bed-sharing, and added sleep deprivation to the mix...



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