Baby colic is one of the most exhausting and emotionally difficult experiences of early parenthood. A baby who cries for hours despite being fed, changed, and held; parents who have tried everything and nothing seems to work; sleepless, stressful evenings that stretch into night. If this sounds familiar, you're in a large and exhausted club — colic affects an estimated 10–40% of infants worldwide. Here's what the evidence actually says about what colic is, why it happens, and what helps.
What Is Colic? The Definition
Colic is defined clinically using the "rule of threes" (Wessel criteria): crying for more than 3 hours per day, more than 3 days per week, for more than 3 weeks, in an otherwise healthy, well-fed infant. It typically begins around 2–3 weeks of age, peaks around 6 weeks, and resolves in most babies by 3–4 months.
Two things the definition doesn't include that parents need to know:
- Colic is a diagnosis of exclusion: It can only be applied after other causes of crying (hunger, pain, illness, reflux) have been ruled out. If your baby is crying excessively, see your pediatrician first.
- The definition says nothing about cause: "Colic" is a description of a symptom pattern, not an explanation. The cause remains incompletely understood.
What Causes Colic? The Evidence So Far
Despite decades of research, there is no single agreed-upon cause of colic. Several theories have evidence:
Gut Microbiome Imbalance
The most current and best-supported hypothesis. Studies consistently find that colicky babies have a different gut microbiome composition than non-colicky babies — specifically, lower levels of Lactobacillus species and higher levels of gas-producing bacteria. This imbalance may cause intestinal inflammation, increased gas production, and pain. This is why probiotic trials (particularly Lactobacillus reuteri) show some of the best evidence for symptom reduction.
Immature Digestive System
A baby's digestive system at birth is still developing. The gut motility, enzyme production, and neural regulation of digestion are all immature in the early weeks. Some researchers believe colic is simply what digestive discomfort feels like during this maturation process.
Cow's Milk Protein Sensitivity
In a subset of colicky babies (estimates range from 10–30%), sensitivity to cow's milk protein — either directly in formula or passed through breast milk from dairy in the mother's diet — may contribute to crying. This is worth trialing an elimination diet for, but it is not the cause in the majority of colic cases.
Neurological / Sensory Processing
Some researchers propose that colicky babies have a lower threshold for sensory stimulation — they become overstimulated more easily and have more difficulty self-regulating. The evening timing of colic (the "witching hour") may reflect accumulated stimulation overload from the day.
Signs That It's Colic (and Not Something Else)
Colic crying has characteristic features:
- Occurs mostly in the late afternoon and evening (often called "the witching hour")
- Baby draws knees toward chest, arches back, clenches fists
- Face flushes red during episodes
- Difficult or impossible to soothe during the episode
- Starts and ends abruptly
- Baby is otherwise healthy, growing well, and calm between episodes
See your pediatrician if: crying is accompanied by fever, unusual stool color, blood in stool, vomiting, weight loss, or if baby doesn't seem well between crying episodes. These suggest something other than colic.
What Actually Helps: The Evidence
L. reuteri Probiotic (Best Evidence)
Multiple randomized controlled trials have shown that Lactobacillus reuteri (DSM 17938 strain) significantly reduces daily crying time in breastfed colicky infants — by up to 50% in some studies. Effect in formula-fed infants is less consistent but still positive in several trials. This is currently the intervention with the strongest evidence base. Discuss with your pediatrician before starting.
Simethicone (Limited Evidence)
Simethicone (the active ingredient in Infacol, Mylicon) breaks up gas bubbles in the gut. It's widely used and generally considered safe, but clinical trial evidence for effectiveness in colic specifically is weak — it performs no better than placebo in most controlled studies. Many parents find it helpful nonetheless, possibly via placebo effect or because gas is contributing in their specific baby.
Maternal Dairy Elimination (For Breastfed Babies)
A 2–3 week strict dairy elimination trial is reasonable if other interventions haven't helped. If colic is cow's milk protein-related, improvement is typically seen within 2 weeks. Reintroduce dairy after 2–3 weeks if no improvement — it's not the cause in the majority of cases and unnecessarily restricting the maternal diet long-term isn't warranted without evidence of benefit.
Soothing Techniques (Help Manage, Don't Cure)
- Motion: Car rides, bouncing, rocking. Rhythmic motion calms many colicky babies temporarily.
- White noise: "Shushing" sounds or white noise apps can reduce crying during episodes. Volume should be moderate — no louder than a shower.
- Swaddling: Reduces the startle reflex and creates a calming womb-like sensation. Most effective in younger babies. See our swaddling guide.
- Skin-to-skin contact: Holding baby against your skin, particularly in a carrier, provides continuous gentle motion and warmth.
- Tummy massage: Gentle clockwise circular massage on baby's tummy, following the path of the large intestine. Can help move trapped gas.
What Doesn't Help
- Herbal teas (fennel, chamomile): Not safe for infants under 6 months; insufficient evidence
- Gripe water: Ingredients vary widely; no clinical trial evidence; some formulations contain sugar or alcohol
- Changing formula brand frequently: Unnecessary unless there's a specific reason to suspect an ingredient
Managing the Emotional Impact
This is not discussed enough. Caring for a colicky baby is genuinely exhausting and psychologically grinding. The relentless crying activates stress responses, interferes with sleep, and can severely strain partnerships and mental health. Colic is one of the strongest predictors of postpartum depression — it is not a coincidence.
Practical strategies:
- Take turns: When one parent has reached their limit, hand baby off. Even 15 minutes in another room helps.
- Put baby down safely and walk away briefly: A baby who is safe in their crib for 5 minutes while a parent collects themselves is better than a parent who is at breaking point. This is not neglect; it's necessary self-preservation.
- Accept help: Specifically and concretely. "Can you take the baby for two hours on Saturday so I can sleep?" is a request people can act on.
- Know it ends: Colic is self-limiting. The vast majority of cases resolve by 3–4 months. In the acute phase, this can feel like cold comfort — but it is true.
For parent wellbeing context, see our postpartum care guide and our honest guide for new parents.