Infant colic — what it is, what it isn't, and what has evidence

Infant colic is one of the hardest experiences of the first months. Previously healthy babies start crying inconsolably, usually in late afternoon or early evening, for hours, with no apparent cause. Parents cycle through breast, change, hold, rocking, fresh air — nothing works consistently. The baby stops on its own, or sleeps, or until the next crisis. And adults end the day exhausted, guilty, and doubting everything.

The good news: it's a benign, self-limiting syndrome with no sequelae. The bad: most interventions sold as solutions have no evidence. This article separates what's known, what isn't, and what really helps — including the part nobody talks about: how parents survive these weeks without harming themselves or the baby.

1. What colic is

The classic criterion was defined by Morris Wessel in 1954, in a seminal article in Pediatrics — the "rule of 3s"^{Wessel et al. 1954}:

Inconsolable crying lasting >3 hours per day, on >3 days per week, for >3 weeks, in a healthy and well-growing baby.

More recent definitions (Rome IV criteria) refined this to avoid requiring 3 weeks (which prolonged family suffering), but the essence is the same: paroxysmal, inconsolable crying in a baby without disease.

Typical features:

• Appears in the first weeks, usually after 2-3 weeks of life
• Peak at 6-8 weeks
• Almost universal spontaneous resolution by 3-4 months
• More common in late afternoon / early evening (the "witching hour")
• Baby may pull legs to abdomen, flush red, appear in pain
• It ends on its own — no intervention is necessary for resolution

It's estimated to affect 15-25% of babies at some level.

2. What it probably isn't

The cause is not established. Some well- and poorly-evidenced hypotheses:

• Immature gut motility: plausible, partially supported by microbiome and intestinal gas studies. But isolated abdominal pain doesn't explain the whole picture.
• Developing microbiome: babies with colic have different gut microbiome — less diversity, less Bifidobacterium and Lactobacillus. Cause or consequence isn't clear yet.
• Transient neural hypersensitivity: the baby may have a regulation threshold still calibrating. Mild stress generates self-feeding crying cycles until the caregiver helps with co-regulation.
• Gastroesophageal reflux: rarely the primary explanation for classic colic. Reflux causes irritability, but the picture differs.

What probably is NOT the main cause:

• Simple gas (despite the popular name)
• Mother's diet (except in specific cases with allergy signs)
• "Bad milk", "weak milk", or folklore variants that blame breast milk
• "Hereditary colic" — without clear genetic support

3. Treatments — what does (and doesn't) have evidence

The Lucassen et al. (1998, BMJ) systematic review consolidated colic treatment trials and was pessimistic^{Lucassen et al. 1998}. Updating with later research:

Without consistent evidence:

• Simethicone: compared to placebo, no significant difference. Still widely prescribed by clinical inertia.
• Homeopathy, generic herbal medicine, non-specific supplements: no evidence.
• Broad restrictive diets for the breastfeeding mother (no dairy, no wheat, no "gas-producing" foods): generally don't work and can harm nutrition and breastfeeding. Only in confirmed cow's milk protein allergy cases (blood in stool, severe eczema) is there reason to exclude dairy under supervision.
• Antispasmodics (dicyclomine): risk > benefit, contraindicated in young infants.

With some evidence (modest):

• Lactobacillus reuteri DSM 17938, in exclusively breastfed babies, showed crying time reduction in several randomized trials. Sung et al. (2014) consolidated the evidence^{Sung et al. 2014}. Effect is modest (about 25 minutes daily reduction on average), more consistent in breastfed, less clear in formula-fed.
• Gentle infant massage: small evidence; useful for contact more than direct gut mechanism.
• Switching to hydrolyzed formula when CMPA is suspected: may help in subgroups. Not for classic colic without other signs.

Behavioral strategies (no robust RCT, but widely shared):

• 5 S's (Harvey Karp): swaddle, side/stomach position (only to soothe, not for sleep), shush (rhythmic white sounds), swing (gentle motion), suck. A combination mimicking the intrauterine environment. Plausible, with observational comfort basis.
• Carrying / babywearing: older studies (Hunziker & Barr 1986) suggest more carrying reduces total crying. Later studies countered this, but the benefit for baby's regulation is clear even without direct effect on colic.
• Movement (stroller, car, swing): immediate calming effect, no strong evidence on total crying time.

4. Period of PURPLE Crying — one of the most important pieces of information

In 2009, Ronald Barr and colleagues published an RCT in CMAJ showing that giving parents structured information about excessive crying (the "Period of PURPLE Crying" concept) reduced incidence of dangerous behaviors with babies^{Barr et al. 2009}. PURPLE is mnemonic:

• Peak of crying — peak at 6-8 weeks
• Unexpected — crying comes and goes without obvious cause
• Resists soothing — may not calm even with everything right
• Pain-like face — baby seems in pain, but isn't
• Long lasting — can last 30-40 minutes or more
• Evening — concentrated in late afternoon/evening

The central message: the crying will stop on its own. You're not doing anything wrong. There's no shortcut. And if you're losing control, place the baby in a safe place and leave the room for a few minutes.

5. The real danger — shaken baby syndrome

This is why this topic deserves a whole pillar, not just a section. Shaken baby syndrome (SBS) — Abusive Head Trauma — is the leading traumatic cause of death and neurological sequelae in babies under 1 year. And it's caused almost exclusively by adults who lost control during prolonged crying spells.

A baby shaken with force suffers diffuse axonal injury, subdural hemorrhage, retinal hemorrhage — often irreversible. No falling needed. No hitting needed. Just being shaken in frustration.

Parents and caregivers need to know:

• Inconsolable crying is normal and passes. Your inability to stop it isn't failure — it's biological design.
• If you're feeling a wave of anger or despair, stop. Put the baby in a safe place (crib, on the floor on a mattress, away from edges), leave the room, breathe for 5-10 minutes. A safe baby crying is better than a dysregulated baby in your arms.
• Warn anyone who cares for your baby — grandparents, nannies, partner — about colic and SBS risk. People who've never cared for a small baby frequently underestimate the physical impact of prolonged crying.

It's not hypothesis. SBS cases by caregivers who "lost patience" are documented in every country. The most effective intervention against SBS is precisely education about what excessive infant crying is.

6. How to survive the colic weeks

Colic ends. Your job is to reach the end intact. Common-sense and perinatal mental health-evidence strategies:

• Take turns. If a couple, alternate who holds the baby in long crying crises. In larger families, request rotation.
• Leave the house daily. Short walk, fresh air, environment change. Lowers cortisol and increases tolerance.
• Use a carrier / sling. Free hands and baby in physical contact activate parasympathetic in both.
• Accept concrete help. Relative who cooks, washes dishes, bathes the baby — helps more than advice.
• Assess your mental health. Colicky baby + sleep deprivation + isolation is a known trigger for postpartum depression. See parents — mental health and adaptation.
• Remember the timeline. 3-4 months. Mark on the calendar and look at it whenever you need.

Tronick (1978), in the famous Still Face study, showed babies are extremely sensitive to caregiver emotional expression^{Tronick et al. 1978}. You don't need to be happy — babies tolerate and even learn from varied expressions. But being regulated, even tired, is different from being dissociated or in collapse. When you feel you're losing regulation, pause.

7. Practical synthesis

1. Colic is benign, self-limiting, and almost universal. Peak at 6-8 weeks, resolution by 3-4 months.
2. Most popular "solutions" (simethicone, diets) lack evidence. Don't waste energy.
3. L. reuteri has modest evidence in breastfed babies. Talk to pediatrician if trying.
4. 5 S's and carrying help through comfort even without strong effect on total crying time.
5. Period of PURPLE Crying is information that can save a life. Share with everyone who cares for your baby.
6. If losing control: stop, place baby safely, leave. A safe baby crying is better than a dysregulated baby in your arms.
7. Care for your mental health. It's not separable from baby care.