Crying, Colic, and the PURPLE Crying Curve: What's Normal in the First Months

Crying is your newborn's main language, and somewhere between weeks two and eight, most parents hit an evening where nothing seems to help. There's a name for this phase - the Period of PURPLE Crying - and understanding it can be the difference between feeling like something's wrong with your baby (or your parenting) and recognizing a normal, well-documented stretch of development that has a clear endpoint. Here's what the research actually shows about crying, colic, and where the line to "call the doctor" really sits.

What PURPLE actually stands for

PURPLE is a memory aid, not a diagnosis. It was developed by researcher Dr. Ronald Barr to help parents recognize a universal pattern rather than assume something is medically wrong: crying that Peaks in intensity week by week before improving, is Unexpected and comes with no obvious trigger, Resists your best soothing efforts, happens alongside a Pain-like face even when baby isn't in pain, is Long-lasting - sometimes several hours a day - and clusters in the Evening. According to the framework, this crying typically starts around 2 weeks of age, peaks around 2 months, and resolves by 3 to 5 months. Every baby experiences some version of it; the intensity is just highly variable from one baby to the next.

What the research says

A 2012 longitudinal study following healthy infants through their first year gives some of the clearest numbers on how common this really is: colic-type fussiness was present in an estimated 53.8% of babies at one month old, dropping to 17.9% by three months. That trajectory - high early, fading fast - lines up closely with the PURPLE framework's peak-then-resolve pattern, and it's a useful data point if you're in the thick of it wondering whether this is forever. It isn't.

A 2024 study using actigraphy (movement-tracking sensors) to follow infants from late pregnancy through eight months found that newborns start out on a short, roughly 12-hour "ultradian" rhythm rather than a true 24-hour one, and that circadian entrainment - a real day/night rhythm - becomes established somewhere between 2 and 4 months, with melatonin production stabilizing around 3 months. That timeline overlaps almost exactly with when PURPLE crying resolves, which is part of why one leading theory is that evening fussiness reflects an immature internal clock still calibrating itself, rather than a digestive problem, an allergy, or a parenting issue.

It's also worth separating crying from reflux, since the two get conflated constantly. A 2019 prospective cohort study found that 72% of babies spit up at least once a day at one month old, and 69% still did at three months - this is physiologic reflux, essentially universal, and it typically resolves on its own by 12 months without any treatment. Spit-up on its own, even a lot of it, isn't evidence that reflux is causing the crying, and it's one of the more common reasons babies end up on unnecessary reflux medication that the evidence doesn't support for otherwise healthy infants.

The honest limitation in all of this: no study has pinned down one single cause for PURPLE crying or colic. Gut motility, an immature nervous system, and differences in gut bacteria have all been proposed, but none is confirmed, and what's actually well established is the epidemiology - how common it is, and how reliably it fades with age - rather than a clean explanation of the mechanism. What the research is fairly clear on is what doesn't help: gas drops and anti-gas remedies haven't outperformed placebo in trials, and probiotics don't have strong evidence behind them either.

Colic vs. PURPLE crying vs. something else

Older clinical definitions of colic use a "rule of three" - crying more than 3 hours a day, more than 3 days a week, for more than 3 weeks - and by that stricter definition, colic affects roughly 15 to 25% of babies. PURPLE crying is a broader, gentler framing: it describes a developmental curve that essentially every baby moves through to some degree, with true colic sitting at the more intense end of that same spectrum rather than being a completely separate condition. The distinction matters less for what you do in the moment (soothe, rotate caregivers, take breaks) and more for your own expectations: for most babies this pattern is developmental rather than a sign of illness — and it is never a reflection of your parenting. The signs below are the ones that mean it's worth a call.

What actually helps, and what to do when nothing does

Responsive soothing - holding, motion, white noise, a change of scenery - helps some babies some of the time, but part of the definition of this phase is that it resists soothing, so it's normal for none of it to fully work on a given evening. A trial of eliminating dairy from a breastfeeding parent's diet is reasonable only if there's a specific reason to suspect a true allergy - a rash, blood in the stool, or forceful vomiting - not for fussiness alone.

If you find yourself at the end of your patience, it is genuinely safe to put your baby down in their crib, step into another room, and take a few minutes to reset. A baby crying alone in a safe crib is not being harmed. Never shake a baby - even a few seconds of shaking can cause permanent brain injury. If you feel close to that point, putting baby down in a safe crib and walking away is the right thing to do, every time - which is part of why this framework exists in the first place, to normalize the crying enough that caregivers have an accepted, guilt-free way to step back when they need to.

It's fair to check in on you, too

Weeks of unpredictable evening crying are genuinely hard on a caregiver's mental health, and it's worth saying plainly: struggling with this phase doesn't mean you're failing, and it's not a character flaw if you feel resentful, exhausted, or teary by week six. If the fatigue and frustration around the crying start to shade into persistent sadness, feeling disconnected from your baby, constant worry you can't switch off, or any thought of harming yourself or your baby, that's worth telling your own doctor about directly and promptly - not just something to push through alone. Postpartum mood and anxiety symptoms are common, treatable, and entirely separate from how well you're handling your baby's crying.

When to call your pediatrician: if crying comes with fever, lethargy, or poor feeding; if you see real vomiting (not ordinary spit-up) or blood in the stool; if the belly looks distended or your baby hasn't stooled in over 24 hours after a normal pattern; if fussiness starts suddenly after 4 to 6 weeks with no prior pattern of it; or if the cry itself sounds different - unusually high-pitched or not like your baby's usual cry. And remember, any rectal temperature of 100.4°F (38°C) or higher in a baby under 3 months is always a same-day, urgent call, crying or not.

Sources

1. Cleveland Clinic. Purple Crying. https://my.clevelandclinic.org/health/articles/purple-crying
2. PMC (2012). Longitudinal Study of Sleep Behavior in Normal Infants during the First Year of Life. https://pmc.ncbi.nlm.nih.gov/articles/PMC4173090/
3. PMC (2024). A Longitudinal Study on Parent-Infant Rest-Activity Rhythms Using Actigraphy From Late Pregnancy to Eight Months After Birth. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11743615/
4. PMC (2019). Natural history of gastroesophageal reflux in infancy: new data from a prospective cohort. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7137340/
5. Mayo Clinic (2024). Fever in Newborns. https://www.mayoclinic.org/healthy-lifestyle/infant-and-toddler-health/in-depth/healthy-baby/art-20047793
6. CDC (2024). Sudden Unexpected Infant Death. https://www.cdc.gov/sudden-infant-death/index.html