Colic typically begins at 2–3 weeks of age — preparing from 34 weeks pregnant for the reality of newborn crying can reduce the shock of the colic period. Colic = inconsolable crying 3+ hours/day, 3+ days/week, for 3+ weeks, in an otherwise healthy baby. Peaks at 6 weeks. Resolves by 3–4 months in 90% of cases. Cause is unknown. Evidence-based help: the 5 S's (swaddle, side/stomach position, shush, swing, suck), babywearing, white noise. What doesn't help: dietary changes (weak evidence), gripe water (no RCT evidence).
Colic is one of those words that gets used loosely — but clinically, it has a precise definition. The most widely accepted diagnostic framework was established by pediatrician Morris Wessel in 1954 and is sometimes called the Rule of 3s: crying that lasts for 3 or more hours per day, occurs on 3 or more days per week, and continues for 3 or more weeks, in an otherwise healthy, well-fed infant.
The phrase "otherwise healthy" is doing a lot of work in that definition. It means that before labelling a baby's crying as colic, other causes — acid reflux, cow's milk protein allergy, infection, hair tourniquet syndrome, hernia — need to have been ruled out. Colic is not a diagnosis of something wrong; it is a clinical description of a crying pattern in a baby who is gaining weight normally, feeding normally, and showing no signs of illness.
Prevalence estimates range from 10 to 25% of infants, depending on the study and the strictness of the criteria applied. The variation in estimates reflects how difficult it is to assess crying duration reliably and consistently across cultures and research settings. What is consistent across studies is that colic affects families across all socioeconomic groups, cultures, and infant feeding methods (both breastfed and formula-fed babies develop colic at similar rates).
It is important to understand that "colic" is a descriptive term, not a disease. Your baby has not been diagnosed with something — they have been described as fitting a pattern that affects a significant minority of infants worldwide and, crucially, resolves on its own.
Colic is not a sign of bad parenting, an insecure attachment, or a problem with your milk. It is not caused by gas in the overwhelming majority of cases (despite the popular belief). It is not something you "gave" your baby. The research consistently fails to identify a single preventable cause — this is not a failure of medical science; it is an honest reflection of a complex phenomenon that probably has multiple overlapping causes in different babies.
The timing of colic is one of the most useful — and genuinely reassuring — things to know. It follows a remarkably predictable trajectory across almost all affected babies, regardless of geography, feeding method, or culture.
Colic typically begins at 2–3 weeks of age. If your baby suddenly seems inconsolable in week two or three, when they seemed relatively settled in week one, this is the characteristic onset. Crying escalates over the following weeks, reaching a clear peak at around 6 weeks of age. The sixth week of life is often the hardest week for families dealing with colic, and knowing this in advance can be genuinely helpful — not because it makes the crying easier to bear in the moment, but because it means you can see the shape of the experience.
After 6 weeks, crying begins to gradually decrease. By weeks 12–16, there is typically significant improvement, and by 4–5 months, colic has resolved in approximately 90% of babies. A small number of babies continue to be "high-need" criers beyond this point, but for most, the peak is firmly in the first three months.
| Timepoint | What to Expect |
|---|---|
| Weeks 2–3 | Colic begins; crying increases beyond normal newborn baseline |
| Week 6 | Peak crying intensity and duration — the hardest week |
| Weeks 12–16 | Significant improvement; most families notice a clear shift |
| Months 4–5 | Resolved for ~90% of babies; occasional fussy periods remain normal |
The 3-month mark is one of the most well-replicated findings in infant development research. Multiple large studies confirm this trajectory. It does not mean you count the days and wait passively — but it does mean that there is a clear, foreseeable end point, even when you are in the middle of the hardest period.
The most accurate, evidence-respecting answer to "what causes colic?" is: we do not know. This is not a placeholder. After decades of research across multiple disciplines, no single cause has been identified that explains colic in most infants. There are multiple competing theories, several of which have partial evidence, but none with sufficient research to be considered definitive.
Gut microbiome differences. Several studies have found differences in intestinal microbiota between colicky and non-colicky infants. Colicky babies may have fewer Lactobacillus species and more gram-negative bacteria, which could produce gas and affect gut motility. This is the basis for the probiotic research discussed below.
Gut motility and hypersensitivity. Some researchers propose that the infant gut is functionally immature in a way that leads to disordered peristalsis or visceral hypersensitivity — meaning the gut walls are more sensitive to normal stimulation than in non-colicky infants. This is analogous to irritable bowel syndrome in adults.
Central sensitisation. Another hypothesis is that colic is partly a neurological phenomenon — an immature nervous system that is not yet efficient at processing and filtering stimulation, leading to states of dysregulation that manifest as prolonged crying.
Parental anxiety transfer. Some studies suggest a correlation between parental anxiety (particularly maternal) and colic, but the direction of causation is unclear. Anxious parents may perceive more crying; alternatively, having a colicky baby causes parental anxiety. This is not a reason to blame parents — it is a reminder that the infant-parent system is bidirectional.
Of all the dietary factors studied, cow's milk protein (CMP) is the one with the most research attention. A small but genuine subset of infants with colic-like presentations actually have cow's milk protein allergy or intolerance (CMPA). In these babies — probably fewer than 5% of all colic cases — dietary elimination is effective.
However, the evidence for dietary elimination (breastfeeding mothers removing dairy from their own diet) as a general colic treatment is very weak. Most RCTs and meta-analyses show no significant benefit for the broader colic population. A 2–3 week elimination trial is sometimes recommended as a diagnostic test — if there is no change, this is strong evidence that dairy is not the issue. For formula-fed babies, a brief trial of hypoallergenic formula may be suggested by a paediatrician if CMPA is suspected.
Pediatrician Harvey Karp introduced the 5 S's method in his 2002 book and it remains the most robustly evidenced behavioural soothing approach for colic. The neuroscience basis is the concept of a "calming reflex" — a neurological switch that, when triggered correctly, can reduce a baby's state of distress rapidly. The 5 S's are designed to activate this reflex by recreating sensory conditions that approximate the womb environment.
The five elements are: Swaddle, Side/Stomach position, Shush, Swing, and Suck. Critically, they work best when applied together and in order. One S alone is often insufficient. The combination produces a cumulative, synergistic effect.
1. Swaddle. Wrap the baby snugly in a thin muslin or blanket with arms straight at their sides. The key is firm but not tight — there should be two finger-widths of space at the chest. Swaddling alone often doesn't calm a baby already mid-cry; it is the foundation on which the other S's work more effectively. Once the baby is calmer, swaddling is also the key to helping them stay calm.
2. Side or Stomach Position. Hold the swaddled baby on their side (or stomach, across your forearm). This position reduces the startle reflex and changes the gravitational relationship between the stomach and the oesophagus, which may reduce discomfort. Note: this is a holding position only — never place a baby to sleep on their side or stomach.
3. Shush. Make a continuous "shhhh" sound, louder than the baby's crying initially, then gradually lower in volume. White noise approximates the constant, loud whooshing of blood flow in the womb, which runs at about 85–90 decibels — louder than most parents imagine. You can also use a white noise machine or app.
4. Swing. Use small, fast jiggles (1–2 inches, not large swings of the body). This mimics the constant movement the baby experienced in utero. The head should be supported; the movement is rhythmic and continuous. As the baby calms, slow and reduce the movement gradually.
5. Suck. Offer a pacifier or finger to suck on. Suckling has a measurable calming effect — it activates the autonomic nervous system's parasympathetic response. It is the final piece after the other four have created the conditions for calming.
Swaddle first, then position, then shush and swing simultaneously, then offer sucking. Attempting these in isolation or in the wrong order is why many parents try the 5 S's and conclude they don't work. The sequence and the simultaneity of the last three elements is what produces the calming response. Practice during a calm moment so you can execute smoothly during a crying episode.
Beyond the 5 S's, several other interventions have been studied. Here is an honest assessment of the evidence for each:
Probiotics (L. reuteri DSM 17938). This is the most promising pharmacological/nutritional intervention for colic, and the evidence base is growing — but still modest. Multiple RCTs have shown that Lactobacillus reuteri DSM 17938 (sold as BioGaia) reduces crying time in breastfed infants with colic. The effect size is meaningful — roughly 45–50 minutes less crying per day. Crucially, the evidence is much weaker for formula-fed babies. This is worth discussing with your paediatrician, particularly if your baby is breastfed.
White noise. Well-evidenced as a soothing tool. See the Shush step above. A dedicated white noise machine placed across the room (not in or adjacent to the crib) is effective both for calming during a crying episode and for improving settling during sleep.
Babywearing. Carrying babies in a sling or soft carrier has been shown in trials to reduce daily crying duration. One often-cited Canadian study found that increased carrying (carrying babies for 3 more hours per day) led to significant reductions in crying — though the effect may be weaker in true colic than in normal fussy babies. That said, babywearing has no meaningful downsides and is worth attempting.
Car rides or motion. Many parents find that car rides provide short-term soothing. The vibration and motion seem to activate the calming reflex. This is a legitimate short-term strategy for getting through a particularly difficult episode, but it is impractical as a long-term approach and does not address the underlying crying pattern.
Sucrose water. Sweetened water has demonstrated calming effects in clinical settings (during procedures) but is not recommended as a home intervention for colic. The evidence does not support using sugar water as a general colic treatment.
The colic supplement market is enormous, which makes it worth being clear about what the evidence actually says for the most popular products:
Simethicone (gas drops). This is one of the most common things parents try — and one of the most thoroughly debunked. Multiple blinded, placebo-controlled RCTs have found simethicone to be no more effective than placebo for reducing colic crying. If your baby is taking it and appears to benefit, the most likely explanation is the placebo effect on the parent (and therefore on the care interaction), or natural resolution coinciding with the intervention.
Gripe water. Formulations vary by country, but no blinded RCT evidence supports the use of gripe water for colic. Some formulations contain alcohol or bicarbonate of soda, which can be potentially harmful. There is no plausible mechanism by which the standard herbal ingredients address the likely causes of colic.
Broad dietary elimination by breastfeeding mothers. As discussed above, unless there is specific reason to suspect a food sensitivity (blood in stools, eczema, persistent congestion alongside the crying), broad elimination diets are unsupported by RCT evidence and can be unnecessarily stressful for a breastfeeding parent who is already exhausted.
Herbal preparations (fennel, chamomile, others). Some small studies suggest possible modest benefits, but the research quality is generally poor, formulations are unstandardised, and regulatory oversight of herbal products is limited. These are not recommended as first-line options.
Discussing colic without explicitly addressing its impact on parents would be a serious omission. The research on parental wellbeing during the colic period is stark: colic is consistently associated with elevated rates of maternal anxiety, paternal frustration, relationship stress, and, in some cases, postnatal depression. It is not an overreaction to say that a screaming, inconsolable baby for three or four hours every evening is one of the most stressful experiences a new parent can face.
One of the most important things to know — and something paediatricians emphasise consistently — is that it is safe to put your baby down in their crib and walk away for 5 minutes. A baby who is crying in a safe place (lying on their back, in a crib, without loose items) will not be harmed by crying for five minutes while you step away, breathe, and decompress. The risk of losing control when severely overstimulated is a far greater danger. Give yourself permission to step away.
Share the load wherever possible. If you have a partner, take turns with colic periods. If you have family support, use it. If you are a solo parent, consider whether there is anyone who can come for a few hours in the evening — the peak colic hours.
It is also worth acknowledging that the despair many parents feel during the colic period is not a sign of weakness or inadequacy. It is a predictable, documented response to a profoundly difficult situation. If you find yourself struggling significantly — not just tired, but genuinely unable to cope — please speak to your GP, midwife, or health visitor. Postnatal mental health support exists precisely for periods like this.
Colic is diagnosed in otherwise healthy babies — but some conditions can present as prolonged crying. Contact your doctor promptly if your baby has: blood in stool, failure to gain weight or weight loss, projectile or continuous vomiting, inconsolable crying accompanied by fever, crying with a specific tender spot (e.g. groin, which may indicate hernia), or if you notice any thread, string, or hair wrapped around a finger or toe (hair tourniquet). These are not colic — they are medical emergencies or conditions requiring evaluation.
Knowing the red flags that distinguish colic from an organic medical cause is critical. Most babies who are "colicky" are genuinely well — but some are not, and the following signs should always prompt medical evaluation:
Blood in stool. Any blood in the nappy — whether red or black (digested blood) — is not normal and requires prompt evaluation. It can indicate milk protein allergy, intussusception, or other GI pathology.
Failure to gain weight or weight loss. Colic does not interfere with feeding in a meaningful way. If your baby is losing weight or failing to gain appropriately, the crying has a cause that is not colic.
Continuous projectile vomiting. Occasional positing is normal. Forceful, projectile vomiting after every feed, or large-volume vomiting, may indicate pyloric stenosis or significant reflux.
Fever with inconsolable crying. A temperature of 38°C / 100.4°F or above in a baby under 3 months, combined with inconsolable crying, always warrants immediate medical assessment.
Crying that suddenly becomes different. If a baby who has been consistently colicky suddenly cries in a qualitatively different way — a high-pitched or unusual cry — this change in quality can indicate a new problem (intussusception, meningitis) and should not be assumed to be colic.
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