Find details here of some of the key original research papers informing this website
The references given here are selected to provide the research evidence behind the key statements made in this website, especially where they may seem controversial or the research is recent.
Copyright restrictions sometimes make it difficult to get hold of original articles. However, many scientific journals now make articles available free, or for a small charge online. Try putting the name of the article into Google Scholar to see if you can get access to it. If you encounter difficulties, your local librarian may be able to help.
The infant crying peak:
Ronald Barr first brought this to widespread attention: Barr R.G. (1990). The normal crying curve: what do we really know? Developmental Medicine and Child Neurology, 32, 356-362.
The reference for the London babies’ crying peak included in this website is: St James-Roberts I., Hurry J., Bowyer J., Barr R.G. (1995). Supplementary carrying compared with advice to increase responsive parenting as interventions to prevent persistent infant crying. Pediatrics, 95, 381-388.
Even trained professionals cannot stop the crying:
St James-Roberts I., Conroy S., Wilsher K. (1995). Clinical, developmental and social aspects of infant crying and colic. Early Development and Parenting, 4, 177-189.
See too: Prudhomme White et al. (2000). Behavioral & physiological responsivity, sleep, and patterns of daily cortisol production in infants with and without colic. Child Development, 71, 862-877.
Most parents of babies who cry a lot provide highly involved, sensitive and resourceful care – and many have had previous babies who have not cried a lot:
St James-Roberts I., Conroy S., Wilsher K. (1995). Links between maternal care and persistent crying in the early months. Child Care, Health & Development, 24, 353-376.
See too: Stifter C., Braungart J. (1992). Infant colic: a transient condition with no apparent effects. Journal of Applied Developmental Psychology, 13, 447-462.
Most babies under 5 months of age who cry a lot are healthy; only about 1% are food intolerant:
Lehtonen L., Gormally S. Barr R.G. (2000). Clinical pies for etiology and outcome in infants presenting with early increased crying. In: Barr, R.G., Hopkins B., Green J. (eds.) Crying as a Sign, a Symptom, and a Signal. London: MacKeith Press/Cambridge University Press.
Note that the 5% rate for organic causes of crying given in this report and elsewhere is for cases taken to physicians because of their crying. Since that does not apply to most babies, the 1% figure for organic causes in infants as a whole is a reasonable estimate.
Infant crying, especially unsoothable crying bouts, can trigger shaken baby syndrome:
Barr R.G., Trent R.B., Cross J. (2006). Age-related incidence curve of hospitalized shaken baby syndrome cases: convergent evidence for crying as a trigger to shaking. Child Abuse & Neglect, 30, 7-16.
See too: Fujiwara T., et al. (2011). Infant distress at five weeks of age and caregiver frustration. Journal of Pediatrics,159, 425-30.
Dads find crying frustrating:
Sahin F., Tasar M.A. (2012). Shaken Baby Syndrome and prevention programs. Turkish Archives of Pediatrics, 47: 150-156.
Shared parenting reduces the impact of infant crying on parents:
Dayton C.J., Walsh T.B., Oh W., Volling B. (2015). Hush now baby: mothers’ and fathers’ strategies for soothing their infants and associated parenting outcomes. Journal of Pediatrics & Health Care, 29, 145-155.
Evidence that limit-setting parenting methods help infants to sleep for long periods at night:
Sleep J., et al. (2002). A randomized controlled trial to compare alternative strategies for preventing infant crying and sleeping problems in the first 12 weeks: the COSI study. Primary Health Care Research and Development, 3, 176-183.
For a contrary view, see: Douglas P.S., Hill P.S., (2013). Behavioral sleep interventions in the first six months of life do not improve outcomes for mothers or infants: a systematic review. Journal of Developmental & Behavioral Pediatrics, 34, 497–507.
Ian St James Roberts, Emeritus Professor of Child Psychology, discusses why some babies cry so much – and have ‘unsoothable’ crying bouts – in the first 3-4 months.
A great deal of research has shown that babies who cry a lot in the first few months and fit the colic picture are in good health. But research into why babies cry in this way – and why some cry more than others – is continuing. Three ideas are currently receiving research.
Because the crying occurs mostly in the early postnatal weeks, one possibility is that prenatal experiences such as maternal stress and anxiety during pregnancy, or difficulties during childbirth, could make some infants irritable. Some studies support this, but others do not and there is no firm evidence for this view.
A second idea is that crying in at least some babies occurs because they lack the ‘good’ bacteria needed for normal digestion or have acquired the wrong types of gut bacteria. This seemed a promising approach and studies in some countries (Italy, Poland and Canada) found evidence that giving droplets of the probiotic Lactobacillus Reuteri to breastfeeding infants reduced their crying. Unfortunately, the largest study, in Australia, failed to find any benefits.
There is no evidence that these probiotics reduce crying in bottle-fed infants, although they are just as likely to cry a lot in early infancy. There are no UK studies and the National Institute for Health and Care Excellence (NICE), which advises the UK government on medical treatments, does not recommend probiotic treatments for infant crying. An obvious concern is that giving bacteria to a baby could do harm, while most infants who cry a lot in the early weeks stop doing so by 3-4 months of age without any dietary change.
This research is continuing. See Sung V, D’Amico F, Cabana MD, et al. Lactobacillus Reuteri to Treat Infant Colic: A Meta-analysis. Pediatrics. 2018;141(1):e20171811; For a critical commentary: St James-Roberts I. Is It Time to Recommend Lactobacillus for Colic? Not Necessarily. Pediatrics. 2018;141(1):e20173445. For a recent report showing the spontaneous decline in infant crying and colic by 12 weeks: Wolke D, Bilgin A, Samara M. Systematic review and Meta-analysis: fussing and crying durations and prevalence of colic in infants. Journal of Pediatrics 2017; 185: 55-61. http://dx.doi.org10.1016/j.jpeds.2017.02.020
The third idea is that prolonged crying in early infancy is due to normal developmental changes in the brain, rather than the gut. The brain undergoes a major reorganisation at around the age when babies cry a lot. For instance, babies lose their ‘primitive reflexes’ (such as the grasp reflex), and social abilities, such as smiling, begin. The idea is that the ‘unsoothable’ crying bouts in this period are due to a temporary loss of control during this brain reorganisation, so that babies cannot stop crying once they have started.
This is an intriguing way to think about the crying, but there is little evidence which directly supports this view. To read more about this explanation, see: St James-Roberts I., Alvarez M., Hovish K. (2013). Emergence of a developmental explanation for prolonged crying in 1-4 month-old infants: review of the evidence. Journal of Pediatric Gastroenterology & Nutrition, 57, Supplement 1, S30-S36.
It is usual to obtain inconsistent findings in any area of research, so that we are probably some way from understanding the causes of ‘unsoothable’ crying in young babies. In the meantime, the evidence that this crying is stressful for parents is much stronger – and provides the basis for the information and guidance on this website.
The impact of the crying on parents is at least as important as the crying itself.
Until recently, the focus in research into infant crying and colic was on the crying and its causes. As evidence grew, it became clear that:
- Most babies who cried a lot were healthy and developed normally.
- Babies in general had a crying ‘peak’ around about 1-2 months of age.
- What upset parents was not the amount of crying so much as the fact that parents (and professionals) could not stop it.
- This ‘unsoothable’ crying, too, was linked to the early months and disappeared with age.
- The crying peak and unsoothable bouts were probably caused by normal developmental processes. (More information on this is given in the research article Why do babies cry excessively?).
Research also showed that the impact of the crying on parents – and consequences for the infant where parents had difficulty coping with it – were at least as important as the crying itself. There is evidence, for instance, that:
- Parents who think the crying means the baby is still hungry can stop breastfeeding too early. Others over-feed their baby.
- The crying can trigger parental distress, frustration and depression.
- This can lead to poor parent-child relationships, problems with child development, and infant abuse in a small number of cases.
In spite of this evidence, there are no routine NHS services to support parents in how to manage the crying.
By providing this website and other evidence-based services which support parents, we hope to improve parental wellbeing, infant outcomes, and the NHS.