Dr. Harvey Karp changed the face of parenting and baby sleep back in 2002 when he first introduced the groundbreaking concept of the 5 S’s for soothing babies in his bestselling book The Happiest Baby on the Block. Within these pages, Dr. Karp explained that mimicking the calming rhythms of the womb—with swaddling, shushing/white noise, swinging, sucking, and holding Baby in the side-stomach position (aka: the 5 S’s)—can activate a baby’s innate calming reflex. This is like their inborn “off switch” for crying and “on switch” for sleep. Cue: The collective sigh of relief from exhausted parents everywhere!

Now, 20+ years later, thousands of trained Happiest Baby educators teach the 5 S’s in hospitals, teen parenting clinics, child abuse prevention programs, WIC centers, military bases, and more across the world. Plus, numerous researchers have studied Dr. Karp’s concept to find out just how impactful and effective the 5 S’s really are. Here, learn all about the science behind what Dr. Karp—and millions of parents—already know: The 5 S’s really do work!

How The 5 S’s Were Discovered

As a young pediatrician determined to help find a solution to colic, Dr. Harvey Karp began to study how parents in other societies soothed their children. That’s when he learned that babies who were born to the !Kung San in Africa were held almost 24 hours a day, constantly getting fed, rocked, and jiggled…and they were virtually colic-free. With that, and some additional research, Dr. Karp realized that these parents, essentially, recreated the cozy, busy, noisy confines of the womb for their little ones, which triggered a neurological response called the calming reflex, which kept babies relaxed.

The truth is, most new parents intuitively know how to calm their babies. For thousands of years, moms, dads, nanas, and grampies have understood that rhythmic sensations, like bouncy car rides, a rumbling hair dryer, pacifier-sucking could quiet a baby’s cries and fussing.

But what everyone overlooked was that these sensations were womb sensations that worked because they turned on a baby’s calming reflex!

Beyond anecdotal evidence from myriad seasoned parents, beyond the advice from your baby’s own pediatrician, and beyond the fact that the 5 S’s is cooked into the curriculum of thousands of parenting classes, there’s honest-to-goodness peer-reviewed studies that shows 5 S’s do, in fact, help keep babies calm and sleeping. Here’s just a taste of what the 5 S’s can do—and how science backs it up!

The 5 S’s reduce crying.

Dr. Karp theorized that the perfect blend of swaddling, rocking, playing white noise, and holding your baby on their tummy or side would help to quell tears. And a randomized 2019 study in the Japan Journal of Nursing Science found that to be true! For this study, some new mothers were taught the how’s and why’s of four out of 5 S’s (researchers left “sucking” out of this study) during a 90-minute training session four weeks after their babies were born. The rest of the moms were not. All the new moms then answered various questions about their babies’ behavior over the course of several months. Six months later it was clear: Infants in the intervention group cried significantly less than the little ones whose parents were not taught Dr. Harvey Karp’s soothing techniques. Another 2019 report, this one the journal PLOS ONE found that the combo of swaddling, white noise, and rocking worked quickly to lower babies’ heart rate and decrease fussiness. 

The 5 S’s improve sleep.

Calming tears, it seems, goes hand-in-hand with promoting sleep. To wit: The Japanese study mentioned above also found that parents who learned the slightly abbreviated 5 S’s had babies who slept significantly longer—and woke up less during the night—than the babies in the control group. Plus, researchers behind the PLOS ONE study note that the sensory stimuli of swaddling, sound, and movement helps babies drift off faster, enter a deeper sleep, and wake less at night. Need more proof? According to a randomized 2016 trial in the journal Pediatrics, engaging in “responsive parenting,” which includes the 5 S’s, was shown to help little ones sleep longer by 35, 25, and 22 minutes at 8, 16, and 40 weeks old. (Responsive parenting means you are aware of your baby’s emotional and physical needs and respond appropriately and consistently.) Plus, a 2022 follow-up study found that the responsive parenting and 5 S’s lessons stuck: The second-born babies of those involved in the original study were more likely to fall asleep in under 15 minutes and snooze 50+ minutes longer per 24 hours period than those in the control group.

The 5 S’s boosts parent confidence.

It’s nearly impossible to feel confident in your parenting abilities from the get-go as a first-time parent. It’s all so new! And you’re so tired! However, a 2020 report found that there is a way to boost confidence…with the 5 S’s. This randomized controlled study in The Journal of Perinatal & Neonatal Nursing looked at two groups of new moms. Some were discharged from the hospital after birth with standard take-care instructions. And the rest received a 20-minute face-to-face lesson on the 5 S’s and given a leaflet on the technique before going home.

Researchers followed up with both groups six to eight weeks postpartum and found that parents who were taught the 5 S’s felt significantly more capable and confident in their parenting abilities than parents who did not learn the 5 S’s. As a bonus, researchers note that feeling this sense of competence is linked to parents’ overall well-being, too. (PS: All the mothers who used the 5 S’s recommended it to other families.)

The 5 S’s ease pain.

Taking your sweet pea in for their regularly scheduled vaccines can be rough. No one wants to see their little one cry after being stuck by a needle! Enter: The 5 S’s. Several studies have found that the good old mix of swaddling, holding your baby in the side/stomach position, shushing, swinging, and sucking can act as a pain-reliever for babies getting shots. One of the most notable studies includes a randomized, placebo-controlled report of 230 infants in the journal Pediatrics. Babies were snugly wrapped in a blanket, placed on their side or stomach, gently shushed and rocked soon after they were given a vaccine at their 2- and 4-month check-ups. (If needed, babies were offered a pacifier, too.) In the end, the 5 S’s babies showed fewer signs of pain, like grimacing, and their crying petered out faster than babies who were not given the 5 S’s. In fact, roughly half of the babies in the control group were still crying after a minute as opposed to just a few of the babies who received the 5 S’s.

The 5 S’s may help preemies.

Preterm babies who are born before 37 weeks of pregnancy often require a good dose of womb-like care after birth. While researchers have yet to delve into the overall impact of the 5 S’s on preemies, there are several studies on how various aspects of the 5 S’s can help our littlest babies. For instance, a 2018 report in the Journal of Maternal-Fetal & Neonatal Medicine found that when premature infants were exposed to Happiest Baby womb-like sounds it helped reduce complications associated with a lack of oxygen and an abnormal heart rhythm. In fact, intermittent hypoxemia and bradycardia significantly declined after sound exposure, which was played intermittently in 6-hour blocks. Another report found that swaddling premature babies in the NICU can help them sleep roughly 35 minutes longer than when unswaddled—and, just like with term babies, swaddling works to help quell pain from a needle stick. Still another study found that preemies’ use of pacifiers (sucking), helped protect against SIDS by increasing their blood pressure and improving the autonomic control of heart rate.

More on the 5 S’s:


Shushing (aka White Noise)



Side/Stomach Position



  • Effect of soothing techniques on infants’ self-regulation behaviors (sleeping, crying, feeding): A randomized controlled study. Japan Journal of Nursing Science. February 2019
  • Infant crying and the calming response: Parental versus mechanical soothing using swaddling, sound, and movement. PLOS ONE. April 2019
  • INSIGHT Responsive Parenting Intervention and Infant Sleep. Pediatrics. July 2016
  • Effect of the INSIGHT Firstborn Parenting Intervention on Secondborn Sleep. June 2022
  • The Effects of an Infant Calming Intervention on Mothers’ Parenting Self-Efficacy and Satisfaction During the Postpartum Period: A Randomized Controlled Trial. The Journal of Perinatal & Neonatal Nursing. June 2020
  • The Effect Of Physical Intervention 5 S’S (Swaddling, Side-stomach, Sushing, Swinging, Sucking) Toward Pain and The Duration of Crying in Infants With DPT Immunization. The Malaysian Journal of Nursing. July 2015
  • Pediatric Intramuscular Injections: Guidelines for Best Practice. The American Journal of Maternal/Child Nursing. March/April 2014
  • Non‐pharmacological management of infant and young child procedural pain. Cochrane Database of Systematic Reviews. October 2011
  • Effective Analgesia Using Physical Interventions for Infant Immunizations. Pediatrics. May 2012
  • A prospective observational cohort study of exposure to womb-like sounds to stabilize breathing and cardiovascular patterns in preterm neonates. Journal of Maternal-Fetal & Neonatal Medicine. June 2017
  • Effects of nesting and swaddling on the sleep duration of premature infants hospitalized in neonatal intensive care units. Iranian Journal of Nursing and Midwifery Research. September 2016
  • Dummy/pacifier use in preterm infants increases blood pressure and improves heart rate control. Pediatric Research. October 2015

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Disclaimer: The information on our site is NOT medical advice for any specific person or condition. It is only meant as general information. If you have any medical questions and concerns about your child or yourself, please contact your health provider.