Six weeks is one of the hardest ages for infant sleep, and there’s a biological reason for it. Your baby’s fussiness is likely peaking right now, their brain hasn’t started producing the sleep hormone melatonin yet, and they may be going through a growth spurt all at the same time. The good news: almost everything that makes six weeks so difficult is temporary and developmentally normal.
Why Six Weeks Is the Peak of Fussiness
Most babies go through a period of increased fussiness that starts around two weeks of age and peaks between six and eight weeks. This is so predictable that researchers have given it a name: the Period of PURPLE Crying. It has nothing to do with the color of your baby’s face. PURPLE is an acronym describing the pattern: the crying peaks around this age, is unexpected, resists soothing, can look painful even when nothing is wrong, lasts for long stretches, and tends to cluster in the evening.
Colic, which is defined as crying more than three hours per day for more than three days per week for longer than three weeks, also peaks at six weeks. It affects roughly 10% to 40% of infants worldwide, and symptoms typically resolve on their own by three to six months. Even if your baby doesn’t meet the formal definition of colic, they’re in the window where baseline fussiness is at its highest. That fussiness shows up most visibly at sleep time, when your baby needs to relax but their nervous system is firing on all cylinders.
Their Brain Can’t Tell Day From Night Yet
Adults fall asleep partly because their brains release melatonin when it gets dark. Your six-week-old’s brain barely produces any. Full-term infants don’t show a reliable day-night rhythm of melatonin until nine to twelve weeks of age, and by that point their melatonin output jumps to five or six times what it was at six weeks. Right now, your baby essentially has no internal clock telling them when it’s time to sleep. They’re fighting sleep because, from their body’s perspective, there’s no hormonal signal saying “it’s nighttime.”
This also explains why your baby might sleep fine during the day but resist sleep in the evening, or seem wide awake at 2 a.m. Their circadian rhythm is still under construction. You can help it along by exposing them to natural light during the day and keeping nighttime feeds dim and quiet, but the real fix is simply time. By about three months, most babies start consolidating their longest sleep stretch at night.
Overtiredness Makes Everything Worse
It sounds contradictory, but the more tired a baby gets, the harder it is for them to fall asleep. At six weeks, your baby can only comfortably stay awake for about one to two hours at a time. That window includes feeding, diaper changes, and any interaction. If you miss the window, stress hormones kick in, your baby gets a second wind, and suddenly they’re wired and crying instead of drifting off.
Watch for early tired cues rather than going by the clock alone. Yawning, staring off into space, and jerky limb movements are signs your baby is ready. If they’re already arching their back, clenching their fists, or turning away from you, they’ve crossed into overtired or overstimulated territory. At that point, reducing stimulation is more helpful than adding it. Lay them on their back in their crib or bassinet, dim the lights, and sit nearby quietly. Sometimes less input is exactly what they need.
The Six-Week Growth Spurt
Six weeks is a common growth spurt window, and growth spurts change feeding patterns in ways that disrupt sleep. During a spurt, babies often want to nurse or take a bottle as frequently as every 30 minutes. This cluster feeding can last a few days and tends to happen in the late afternoon and evening, right when you’d expect your baby to be winding down for the night.
A baby who’s hungry won’t settle to sleep no matter what soothing technique you try. If your baby falls asleep briefly and then wakes up rooting or sucking on their hands, hunger is the likely culprit. Feeding on demand during a growth spurt, even if it feels constant, helps your baby get through it faster. These spurts are short-lived, usually wrapping up within two to four days.
The Startle Reflex Wakes Them Up
Even when your baby does fall asleep, the Moro reflex (the startle reflex) can jolt them awake seconds later. This reflex is strongest in the newborn period and lasts until about four to six months. When your baby’s arms fling outward suddenly, it triggers a sensation of falling that wakes them, and then you’re back to square one.
Swaddling works specifically because it keeps your baby’s arms secure against their body so the reflex can’t complete its motion. A properly swaddled baby startles, feels the resistance of the wrap, and stays asleep instead of waking up crying. Use a firm, flat sleep surface with no loose blankets, pillows, or stuffed toys in the space. Place your baby on their back, and stop swaddling once they show any signs of rolling over.
Overstimulation in the Evening
By the end of the day, your six-week-old has taken in more sensory information than their developing brain can process. Visitors, TV noise, bright lights, being passed between people: all of it accumulates. The evening “witching hour” that many parents describe is partly the result of sensory overload with no melatonin to help the brain wind down.
Signs of overstimulation include turning their head away from you, clenching their fists, waving their arms and legs frantically, and pulling away from touch. These look a lot like sleep fighting because they are. Your baby wants to shut down but can’t. A predictable wind-down routine in a dim, quiet room helps signal that it’s time to transition. You don’t need an elaborate bedtime ritual at this age. Dimming lights, gentle rocking, and white noise are enough to lower the sensory volume.
When Something Else Might Be Going On
Most sleep fighting at six weeks is completely normal, but a few signs point to something that needs medical attention. For any baby under three months, a fever of any degree warrants a call to your pediatrician. Also call if your baby is producing fewer wet diapers than usual, crying without tears, or has a dry mouth, as these are signs of dehydration. A sunken soft spot on the top of the head is another dehydration signal.
Missing two or more feedings in a row, vomiting forcefully after feeds (not just spitting up), or being unusually difficult to wake are also reasons to get in touch with your doctor. Sleep fighting that comes with excessive sleepiness or floppiness is different from the normal fussy resistance you’d expect at this age. Trust your instincts. You know what your baby’s baseline fussiness looks like, and a sudden change from that baseline is worth a phone call.