What causes colic? According to a popular definition, colic is excessive crying or fussing in an otherwise healthy baby.
It's the catch-all term doctors use to describe intense, inconsolable crying when they aren't immediately sure what's going on.
So there isn't any single answer or remedy. Different babies cry for different reasons.
In some cases, there may be a feedback loop, ratcheting stress back and forth between infants and parents. Babies cry and distress their parents. Then they sense their parents' stressed out vibes and become even more upset.
In other cases, babies might be especially cranky because their hormonal rhythms aren't in sync with the natural, 24-hour day. They might need better circadian cues -- more exposure to sunlight during the day, and less exposure to artificial light (and social excitement) at night.
It's also likely that some babies simply have a more difficult time calming down after something disturbs them. With sensitive, responsive care and patience, these babies will eventually develop the more mature nervous systems and learn to settle down.
But as many parents know, colicky babies often give the impression that they are in pain, and research supports the idea that some babies are suffering from painful medication conditions, including cow's milk protein intolerance and migraine.
Moreover, there is mounting evidence that infantile colic is linked with a distinctive physical profile:
Twenty-first century studies have consistently found that "colicky" babies have a different mix of bacteria colonizing their intestines.
This is where the latest research takes us. Some species of intestinal bacteria are beneficial;
others are potentially troublesome. When infants have the wrong mix, they are
more likely to develop symptoms of colic. Why? What causes colic symptoms in
babies with too much of the wrong bacteria?
Researchers are still putting together pieces of the puzzle. But the general idea is high concentrations of certain bacteria can cause intestinal inflammation. In addition, they may prompt babies to grow more pain receptors in the gut, making the babies more sensitive to potentially painful stimuli (Pärtty and Kalliomäki 2017).
As a result, something that doesn't bother the average baby much -- like passing gas -- might cause a lot of distress in the colicky infant.
Here are the details.
For centuries people assumed that infantile colic was caused by abdominal pain. But this assumption became controversial in the 20th century, so the medical profession adopted new definitions of colic that made no reference to causation.
For instance, some doctors follow the "rule of
three." A baby is considered colicky if he is "otherwise healthy and
well-fed" but cries for more than 3 hours each day, for more than 3 days
each week, for at least 3 consecutive weeks (Wessel 1954; Sijmen et al 2001).
Under this definition, "colic" is really just another label for "excessive crying," which could be caused by a wide variety of things, including conditions completely unrelated to abdominal pain (or physical pain of any kind).
In fact, by specifying that the baby be "otherwise healthy," this definition essentially rules out diseases and ailments as causes of colic. We're left with other possibilities, like these:
The last is probably the most straightforward to remedy: Parents simply need to carry their babies more, and make sure they are responding promptly when babies need soothing. But it's not clear how often this really is the problem. Many parents are desperate precisely because their babies are crying despite a lot of highly responsive care!
What should parents do if one of the other factors is to blame?
To some degree, it's a waiting game. Whereas about 25% of babies satisfy the "rule of three" at 6 weeks postpartum, less than 1% of babies are still crying this much at 10-12 weeks (Wolke et al 2017). But understanding these factors might help you speed up the time it takes for your baby to improve.
Whether your baby is high strung, or just going through a temporary developmental phase, it makes sense to tune into what situations trigger your baby's crying jags, and then avoid those situations. See this article about reducing stress in babies.
It also makes sense to review your own stress levels. Caring for a colicky infant can be frustrating and exhausting, and it's a leading cause of dangerous parental lapses. People are more likely to shake infants when they are exhausted, stressed, and frustrated, and shaking can cause infant brain injuries (Barr et al 2006; Lopes and Williams 2016). As I explain here, your mental health should be a top priority.
Finally, parents can do a lot to help their babies develop mature circadian rhythms. During the daytime, include your baby in family activities, and expose him or her to sunlight. After the sun goes down, keep the lights dim, and reduce stimulation.
"No pain, no illness" explanations of infantile colic have gotten a lot of attention over the years. Indeed, doctors have been counseled to reassure parents that "in 95% of cases, no physical or health problems are found" (Akhnikh et al 2014).
But this statistic is misleading. It reflects studies that define infantile colic as excessive crying in an "otherwise healthy" infant.
Obviously, such a definition is going to lead to an apparently low rate of "physical or health problems" among colicky babies. We're not going to find as many physical problems if we select from a group of individuals who don't seem to have any physical problems in the first place!
We get different results if we expand our criteria for "colic" to include symptoms like these:
Babies exhibiting these signs are more likely to have an underlying medical condition, so if you observe them, you should consult your doctor. This is especially important if your baby has a hard, distended abdomen and flexed legs, symptoms that can sometimes indicate an intestinal obstruction, or intussusception. It's a rare condition, but a dangerous one, so be sure to seek medical advice right away.
Other, less dire, conditions linked with excessive fussing or crying include:
Most of these aren't common causes of colic either. But some babies do experience these problems, so it makes sense to report any symptoms you observe to your doctor.
What about the old idea that colicky babies cry because they have highly quantities of gas passing through their intestines? That notion hasn't received much scientific support.
Studies have failed to find evidence that colicky babies harbored more intestinal gas than other infants (Illingworth 1954; Taylor 1957). And studies of simethicone -- a popular over-the-counter treatment for excessive gas -- have failed to establish it as an effective remedy for colic (Biagoli et al 2016).
By contrast, a stronger case can be made for two newer ideas.
First, there is infantile migraine.
Studies show that babies are more likely to suffer from colic if migraines run in the family (Gelfand et al 2012). In addition, babies are more likely to develop migraines later in life if they experience infantile colic (Romanello et al 2013; Sillanpää and Saarinen 2015).
Researchers don't yet know if colicky babies are experiencing symptoms similar to those suffered by an older individual having a migraine, but the connections are strong enough to warrant concern (Gelfand et al 2015; Qubty and Gelfand 2016).
Second, there is the hypothesis that colic is caused by high concentrations of potentially troublesome bacteria in the gut.
Studies conducted in Italy, Canada, and Poland report the
same thing: Babies who develop colic have higher than normal
concentrations of bacteria that can cause gas and inflammation (DuBois and
Gregory 2016; Pham et al 2017; Pärtty and Kalliomäki 2017; Savino et al
Colicky babies may also have lower than normal concentrations of the "good" bacteria, probiotics like Lactobacillus and Bifidobacteria (deWeerth et al 2013).
So differences in gut flora are linked with colic. But what causes colic symptoms? One idea that colicky babies have inflammation of the gut, a hypothesis consistent with observations that colicky infants are more likely to test positive for show biomarkers of low-grade inflammation (Pärtty et al 2017).
In addition, researchers speculate that an unfavorable mix of bacteria could lead babies to develop more pain receptors in the gut, rendering them more sensitive to potentially painful stimuli (Pärtty and Kalliomäki 2017). As a result, something that doesn't bother the average baby much -- like a little extra gas -- might cause a lot of distress in the colicky infant.
All of this suggests a possible therapy. Can we improve colic symptoms with a treatment of probiotics?
Controlled, double-blind studies suggest that daily supplements of Lactobacillus reuteri can reduce crying times by as much as 50% (Baldassarre et al 2018; Savino et al 2017; Shreck et al 2017; Chao et al 2015; Sung et al 2013; Szajewska et al 2012; Savino et al 2006). But researchers say it's too early to view probiotics as a cure-all.
For one thing, most studies of Lactobacillus reuteri concern breastfed babies. When researchers reviewed the best research published to date, they noted that "the evidence of the probiotic’s effectiveness in formula-fed infants is limited" (Sung et al 2014).
In addition, not every study has shown improvements over the placebo. In Italy, Poland, and Canada, probiotics seem very helpful. But studies conducted in Australia and the United States failed to find any benefits (Sung et al 2014; Fatheree et al 2017).
One explanation is that the effects of probiotics depend on what is already living in an infant's gut. Different babies -- living in different regions and exposed to different diets (through breast milk) -- may have different bacterial ecosystems. The ability of supplements of Lactobacillus reuteri to replace troublesome bacteria may depend on these differences. Thus, we can't assume that probiotics that work in Italy will have the same effect in the United States (St. James-Roberts 2018).
So are probiotics worth trying? For most babies, they are probably safe. But check with your pediatrician first. In some patients—such as those with impaired immune systems—probiotics could cause problems. Moreover, the quality of over-the-counter probiotics vary greatly, and different species or strains of probiotics work differently.
"What is colic?" explains different ways that researchers have defined infantile colic, and provides an overview of some of the most likely reasons for excessive crying.
"Infant crying" talks more broadly about what kinds of crying and fussing are normal for babies, what can reduce crying in healthy babies, and what sets colicky babies apart.
"Colicky babies: Understanding the effects of temperament, brain chemistry, and pain sensitivity" explores the idea that we should look to the nervous system to discover what causes colic.
For full citations of the studies mentioned in this piece, see this bibliography.
Content of "What causes colic" last modified 2/2018
Image credits for "What is colic":
Title image of angry baby by Morgan / flickr
Closeup image of crying infant by Tatiana Vdb / flickr
Image of bacteria, Lactobaccillus casei, by AJC1 / flickr