Babies are born with a very limited ability to shiver. Unlike older children and adults, newborns rely almost entirely on a special type of body fat called brown fat to generate heat when they’re cold. True, purposeful shivering doesn’t become a reliable warming mechanism until a baby is several months old, and it continues to develop through toddlerhood. If you’re noticing shivering-like movements in a young baby, there are several possible explanations, and not all of them involve being cold.
How Newborns Stay Warm Without Shivering
Adults shiver automatically when cold. Muscles contract rapidly, generating heat. Newborns can’t do this effectively because their muscle mass is too small and their nervous system is still maturing. Instead, they depend on a process called non-shivering thermogenesis, which is powered by brown adipose tissue (brown fat). This specialized fat, found around the shoulders, kidneys, and spine, breaks down and releases heat directly into the bloodstream without any muscle movement at all.
Brown fat is metabolically different from the regular white fat that stores energy. When a baby is exposed to cold, brown fat cells activate and essentially burn calories to produce warmth. This is a newborn’s primary defense against cold temperatures, along with vasoconstriction, where blood vessels near the skin narrow to keep heat concentrated in the body’s core. The shivering reflex gradually becomes more effective over the first six to twelve months, though the exact timeline varies from baby to baby.
What Shivering-Like Movements Actually Mean
Many parents notice trembling, jittering, or brief shaking episodes in young babies and wonder if their baby is cold. In most cases, these movements aren’t shivering at all. Newborns commonly have tremors or jitteriness, especially in the first few weeks of life, because their nervous system is still immature. These tremors are usually harmless and tend to happen when the baby is startled, crying, or transitioning between sleep states.
There’s a simple way to tell a benign tremor from something more concerning. A normal tremor can be triggered by a sudden noise or touch, and it stops when you gently hold the affected limb still or let the baby suck on a finger or pacifier. It won’t involve unusual eye movements or changes in breathing. A seizure, by contrast, typically can’t be stopped by gentle restraint, may involve forced eye deviation, and can be accompanied by pauses in breathing or other changes.
Another common movement is benign neonatal sleep myoclonus, which looks like rhythmic jerking of the arms or legs during sleep. It can be alarming to watch, but it’s not a seizure. The key difference: it only happens during sleep and stops immediately when the baby wakes up. Unlike adult sleep twitches, which tend to be a single asymmetric jerk, these movements in newborns are often bilateral and repetitive.
When Babies Actually Start Shivering
There’s no single birthday when the shivering reflex “turns on.” It develops gradually. Most full-term infants begin to show some shivering capability between 3 and 6 months of age as their muscle mass increases and their neurological control matures. By around 12 months, the response is more consistent, though still not as efficient as in older children. Brown fat stores decline over the first year of life as shivering takes over as the dominant way to generate heat.
Premature babies are at a particular disadvantage. They have less brown fat, less body fat overall, a higher surface-area-to-body-weight ratio, and thinner skin, all of which make heat loss faster and heat production harder. Their shivering reflex may take even longer to develop.
Cold Stress Signs to Watch For
Because young babies can’t shiver to warm up, the usual adult signal of “I’m cold” is missing. Instead, cold stress in an infant shows up differently. Signs include cool skin (especially on the hands, feet, and chest), bright red skin coloring, unusual stillness or lethargy, and weak feeding. A body temperature below 95°F (35°C) is considered hypothermia and needs prompt medical attention.
The best way to prevent cold stress is to keep the room at a comfortable temperature, generally between 68°F and 72°F (20°C to 22°C), and dress your baby in one more layer than you’d wear yourself. Avoid heavy blankets in the crib. A sleep sack or wearable blanket is a safer option. You can check whether your baby is too cold by feeling the back of the neck or the chest rather than the hands or feet, which tend to run cool naturally in infants.
Shivering With a Fever
If your older baby (roughly 6 months and up) shivers during an illness, it’s likely rigors, the chills that accompany a rising fever. This happens because the brain temporarily resets the body’s thermostat higher, so the body perceives its current temperature as “too cold” and triggers shivering to generate more heat. It can look dramatic, but short episodes of chills during a fever are common.
If your baby has shaking chills that last more than 30 minutes, that warrants a call to your pediatrician. For comfort during a brief episode of chills, a light blanket can help. A rectal temperature of 100.4°F (38°C) or higher is considered a fever. In babies 3 months or younger, any fever at that threshold needs immediate medical evaluation. Between 3 and 6 months, a fever of 101°F (38.3°C) or higher warrants a call. Over 6 months, the threshold is 103°F (39.4°C), or any fever where the baby seems especially uncomfortable or unwell.
When Shaking Could Signal Something Else
Occasionally, trembling or shaking in a newborn points to a metabolic issue rather than temperature regulation. Low blood sugar (neonatal hypoglycemia) can cause tremors, shakiness, sweating, and in severe cases, seizures. This is more common in babies who are premature, small for gestational age, or born to mothers with diabetes. Hospitals routinely screen at-risk newborns, but symptoms can appear after discharge.
The bottom line: occasional brief trembling in a newborn is almost always normal jitteriness, not true shivering. If the movements stop when you gently hold the limb or offer a pacifier, that’s reassuring. Persistent, rhythmic, or uncontrollable movements that don’t respond to touch, involve eye changes, or come with breathing irregularities are a different story and should be evaluated promptly.