Colic in Newborns: The Rule of Threes, What Actually Helps, and When to Call the Doctor

Some evenings, around dinnertime, your baby starts crying and doesn't stop. Not fussing. Not the little grumble that a burp or a fresh diaper fixes. Real crying — long, red-faced, back-arching, legs-drawn-up, nothing-you-try-works crying. Two hours in you have tried the bottle, the swaddle, the swing, the sling, and a slow lap around the kitchen, and your baby is still screaming, and you are quietly starting to wonder what is wrong with your baby, and with you.

There is a name for that. It is colic, it is astonishingly common — as many as one in five infants go through it, according to the medical review at StatPearls — and the two things that matter most about it are also the two things nobody tells you in the hospital. First: nothing you did caused it. Second: it ends. This post is what the AAP, Cleveland Clinic, Seattle Children's, and the National Center on Shaken Baby Syndrome actually say about colic — the definition, the timeline, what helps, what doesn't, and the one safety rule that matters more than any of the soothing tricks.

01What colic actually is

Colic is the name doctors give to a specific pattern of crying in an otherwise healthy baby. The classic definition, called the Wessel criteria or the "Rule of Threes," is crying "for more than three hours a day, at least three days a week, for more than three weeks," in the words of the Cleveland Clinic. StatPearls puts it the same way and notes that modern clinicians have relaxed the third clause — a baby who has been crying that intensely for two weeks probably qualifies. The important word in that definition is healthy: colic is what is left after a doctor has ruled everything else out.

Cleveland Clinic's short version is honest: colic is when an "otherwise healthy baby cries excessively for no clear reason." The American Academy of Pediatrics describes the same pattern without using the phrase — fussy crying that "usually peaks at about 3 hours a day by 6 weeks old" and then tapers off. Roughly one in five infants goes through it, per StatPearls, which means if you know five families with a newborn, one of them has lived through this.

02When it starts, peaks, and ends

Colic follows a fairly predictable arc, and knowing the shape of it helps. The AAP says it "usually [starts] between the second and fourth weeks," peaks near six weeks with fussy crying of about three hours a day, and "stops by 3 to 4 months, but it can last until 6 months of age." Cleveland Clinic puts the peak at "between 4 and 6 weeks of age" and says colic "usually ends rather abruptly when your baby is 3 to 4 months old." StatPearls agrees: symptoms "reach their peak around 6 weeks and typically resolve by the age of 12 weeks." In practice, that means the very worst nights are usually behind you before your baby is two months old.

03What it looks like

Colic crying does not sound like ordinary fussing, and the body language is distinct enough that the AAP and Cleveland Clinic describe it in almost the same words.

• Inconsolable screaming. The AAP writes that "colicky babies cry inconsolably, often screaming" — with the crying continuing no matter what you try.
• A bright red or flushed face. Cleveland Clinic notes the face "turning bright red or a deeper shade after long periods of crying."
• Legs pulled up, back arched. Both the AAP ("extending or pulling up their legs") and Cleveland Clinic ("legs curled up over their tummy, arched back") describe the same posture.
• Clenched fists and a hard, swollen belly. Per Cleveland Clinic.
• Passing gas. Both the AAP and Cleveland Clinic list this as common during a colic episode — though it is usually a result of gulping air while crying, not the cause of it.
• Evening clustering. The AAP notes the crying "often become[s] worse in the early evening." If your baby is calm all day and comes apart at dinnertime, that is textbook. Our post on the newborn witching hour covers the milder version of the same pattern.

04Why babies get it

The short, honest answer is that no one is sure. Cleveland Clinic states that researchers "don't know the exact reason babies get colic." The AAP is equally blunt: "There is no definite explanation for why this happens." The best current guess, in the AAP's own words, is that a colicky baby "is unusually sensitive to stimulation" — that an immature nervous system, still learning to filter the world, is overwhelmed by ordinary input and unable to shut it down. Other possible contributors that Cleveland Clinic lists include gas, reflux, food or milk-protein sensitivity, over- or underfeeding, and general sensory overload. What the sources agree on is what it is not: it is not caused by anything you did or didn't do.

05The Period of PURPLE Crying

There is another way to think about all of this — a framework developed by the National Center on Shaken Baby Syndrome to help parents understand that even extreme crying in a healthy infant is normal, and that has since been adopted by children's hospitals across the country. It is called the Period of PURPLE Crying, and each letter stands for a feature of the crying that catches new parents off guard. This is the version Seattle Children's and Cleveland Clinic both use:

• P — Peak of crying. "Your baby may cry more each week, the most in month 2, then less in months 3-5" (Seattle Children's).
• U — Unexpected. "Crying can come and go and you don't know why."
• R — Resists soothing. "Your baby may not stop crying no matter what you try."
• P — Pain-like face. "A crying baby may look like they are in pain, even when they are not."
• L — Long-lasting. "Crying can last as much as 5 hours a day, or more."
• E — Evening. "Your baby may cry more in the late afternoon and evening."

The reason the framework matters is that it names, in advance, the things about the crying that make you think something must be wrong. Nothing is wrong. Cleveland Clinic's summary of the pattern: it starts "around 2 weeks of age," peaks "during the second month of life," and ends "around 3 to 5 months of age." That is the same window as colic — because they are the same phenomenon described two different ways.

06What actually helps

There is no cure for colic, because there is no single cause to cure. What there is, is a set of soothing techniques that make the crying shorter and less severe — most of which mimic the environment inside the womb. Here is what the AAP and Cleveland Clinic actually recommend.

07What probably will not help

A lot of things are marketed as colic cures. Most of them do not work, and it is worth knowing that going in so you do not spend a Tuesday chasing miracle drops. The StatPearls medical review is direct: "Most simethicone studies show no effect" (that is the active ingredient in Little Remedies Gas Drops and Mylicon), prescription antispasmodics like dicyclomine "carry safety risks," and proton pump inhibitors "are ineffective" unless a baby actually has reflux disease.

Probiotics are a gentler in-between. StatPearls notes that Lactobacillus reuteri has shown "reduction in crying time" in some studies of both breastfed and formula-fed babies, but "results remain inconsistent." It is not a proven cure and you should talk to your pediatrician before starting one, especially in the first weeks. Gripe water is not FDA-regulated for infants and its formulations vary widely. In every credible source we read, the answer to "what fixes colic in a bottle" was the same: nothing yet does.

08The most important safety rule

This is the part of the article that matters more than any of the tricks above. The National Center on Shaken Baby Syndrome built the entire Period of PURPLE Crying program around one insight: the reason infants get shaken is not that parents are cruel. It is that a healthy adult, held at the end of their rope by hours of unstoppable crying, sometimes snaps. Colic is exactly the crying that produces that moment. The prevention is knowing about the moment in advance and having a rule to fall back on.

That rule, in the AAP's exact words, is this: "Place your baby in a safe place, such as [a] crib or playpen without blankets and stuffed animals; leave the room; and let your baby cry alone for about 10 to 15 minutes." Then, still per the AAP: "It is never safe to shake, throw, hit, slam, or jerk any child." Cleveland Clinic says the same thing in one sentence: "Never shake your baby, no matter how frustrated you get. This can cause bleeding, bruising and swelling in your baby's brain."

09When to call the doctor

Colic is a diagnosis of exclusion, which means it is what a doctor lands on after ruling other things out. Anything on this list is a reason to call. Cleveland Clinic and the AAP list the same red flags.

• A fever in a baby under two months. The AAP is explicit: "If your baby is younger than 2 months and has a fever, call your child's doctor right away." Our post on newborn fever and when to call covers what counts as a fever and what to do next.
• Forceful vomiting, or vomit that is green or bloody. Cleveland Clinic lists this as a call-the-doctor sign.
• Diarrhea or blood in the stool. Same source. Blood in a diaper is always worth a call.
• Losing weight, or not gaining it. Per Cleveland Clinic, and the AAP's own note that a baby who "is fussy after feeding, has excessive spitting or vomiting, and is losing or not gaining weight" needs to be seen.
• A sudden, new change in behavior — a baby who was fine and is now inconsolable in a different way, or lethargic between crying jags, or refusing to eat entirely.

10It ends. And you are not alone.

The colic weeks are one of the hardest stretches of the first year for reasons the parenting books tend to soft-pedal: nothing you try consistently works, you cannot sleep, and your job is to keep loving a small person who screams at you for four hours every evening. It gets better. Every one of the sources above puts the end of it at three to four months, and by six months it is nearly universally over.

Between now and then, the AAP's soothing kit is a real help and the ten-minute walk-away rule is a lifesaver. And if you are past the point where advice is what you need — if you need an actual person to take a night — our night help page explains what a night nanny, a newborn care specialist, and a postpartum doula each do, and what a real one costs.

Questions parents actually ask

Newborn Weeks is planning help, not medical advice — always follow your own doctor, midwife, or pediatrician.