Possetting is the effortless flow of a small amount of milk from a baby’s mouth during or shortly after a feed. It’s completely normal, affects roughly 72% of one-month-old infants, and is not a sign of illness. The term is used mainly in the UK and Australia, while “spitting up” is the more common phrase in the United States. Either way, it describes the same thing: a mouthful or two of milk that oozes back up without any force or distress.
Why Babies Posset
At the top of the stomach sits a ring of muscle that acts like a valve, keeping food down once it’s been swallowed. In adults, this valve stays tightly closed between swallows. In newborns, it’s still immature and relaxes at the wrong times, allowing milk to slip back up through the food pipe and out of the mouth. Most possetting episodes happen during these brief, spontaneous relaxations of the valve, unrelated to swallowing.
A smaller number of episodes occur when pressure inside the abdomen rises suddenly, such as during crying, straining, or being placed on the tummy, and the valve can’t tighten quickly enough to keep the milk in place. A baby’s stomach is also tiny and sits at an angle that makes backflow easier. Combined with an all-liquid diet, this means some degree of possetting is almost unavoidable in young babies.
How Common It Is
A prospective study tracking infants from birth found that 72% of babies posseted at least once a day at one month old. The rate stayed high at three months (69%), then started to drop: 56% at six months, 18% at ten months, and just 13% by the first birthday. The peak for normal, everyday possetting was around three months of age, when about 60% of infants were doing it regularly.
Most babies bring up only one or two mouthfuls at a time. It often looks like more than it actually is once it spreads across a bib or muslin cloth.
Possetting vs. Vomiting
The key difference is effort. Possetting is passive. Milk dribbles or oozes from the mouth, sometimes alongside a burp, with no visible strain. Vomiting involves the stomach muscles contracting forcefully, shooting the contents out of the mouth. A baby who is vomiting will often look distressed or uncomfortable beforehand, while a baby who possets may not even seem to notice.
Occasional vomiting on its own isn’t necessarily alarming in a young baby. But regular forceful vomiting, especially if it’s projectile, is a different situation from routine possetting and worth having checked.
Common Triggers
Certain feeding and handling patterns can make possetting worse:
- Overfeeding. A stomach that’s too full is more likely to overflow. Smaller, more frequent feeds reduce the volume sitting in the stomach at any one time.
- Swallowed air. Air bubbles take up space and can push milk back up when they rise. A bottle nipple with too large a hole lets milk flow too fast, causing the baby to gulp air along with it.
- Movement after feeding. Bouncing, tummy time, or placing a baby in a car seat right after a feed increases abdominal pressure and encourages milk to come back up.
- Flat positioning. Lying a baby down immediately after a feed removes gravity’s help in keeping milk down.
Practical Ways to Reduce It
You can’t eliminate possetting entirely while a baby’s valve is still maturing, but a few adjustments tend to make a noticeable difference. Hold your baby upright for 15 to 30 minutes after each feed. When burping, sit the baby upright on your lap rather than over your shoulder, since shoulder burping puts pressure directly on the stomach. Pat the back gently with the baby leaning slightly forward at the waist.
If you’re breastfeeding, try offering just one breast per session rather than switching sides. For bottle-fed babies, offering smaller amounts more frequently can help. Check that the bottle nipple isn’t flowing too fast. Avoid vigorous play or jostling during and right after feeds.
Thickened formula is sometimes suggested for babies who posset heavily. One study found that cereal-thickened formula significantly reduced the frequency of possetting compared to upright positioning alone, and the babies on thickened formula also took in roughly 25% more calories, leading to greater weight and length gains. This is worth discussing with your health visitor or pediatrician if possetting is frequent enough to concern you.
When Possetting Stops
Most babies start to posset less around six months, when they begin spending more time upright and start solid foods. By 12 to 14 months, the vast majority have stopped entirely. The valve at the top of the stomach strengthens with age, the stomach grows, and the shift to thicker foods all work together to resolve it.
Signs That Something Else Is Going On
Normal possetting happens in a baby who is otherwise happy, feeding well, and gaining weight on track. A small number of infants, roughly one in five at the one-month peak, have reflux that crosses into territory doctors consider problematic. Warning signs include:
- Poor weight gain or weight loss. If enough milk is coming back up to affect nutrition, the baby may fall behind on growth charts.
- Refusing feeds or loss of appetite. A baby who arches away from the breast or bottle, or who seems to associate feeding with pain, may have irritation in the food pipe.
- Persistent irritability. Fussiness that’s clearly tied to feeding or lying down, beyond normal infant crankiness.
- Arching of the back, abnormal neck or chin movements. These can signal discomfort from acid irritating the food pipe.
- Breathing problems. Coughing, wheezing, choking, or gagging during feeds.
- Unusual vomit. Vomit that contains blood, looks like coffee grounds, or appears green or yellow (bile-stained) needs prompt attention.
Also worth noting: possetting that begins for the first time before two weeks of age or after six months of age falls outside the typical pattern and is worth investigating, since it may point to a different underlying cause.