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.