Most common baby illnesses last between 3 and 14 days, depending on what’s causing them. A simple cold typically clears up in 10 to 14 days, while something like an ear infection may resolve in as few as three. Knowing the typical timeline for each illness helps you gauge whether your baby is recovering on schedule or needs medical attention.
Common Colds: 10 to 14 Days
Colds are the illness you’ll deal with most often. Babies catch an average of 6 to 8 colds per year, and each one takes about 10 to 14 days to fully clear. The first few days usually bring the worst congestion, fussiness, and possible low-grade fever. By the middle of the first week, the runny nose is still going strong, but your baby will likely start acting more like themselves. The tail end of a cold is mostly a lingering runny nose and occasional cough.
What catches many parents off guard is how long “normal” actually is. Two full weeks of sniffles can feel like forever, but it’s completely typical. And because babies catch colds so frequently, one illness can blur into the next, making it seem like your baby is sick constantly. If your baby is in daycare, this is especially common during fall and winter months.
RSV and Bronchiolitis: 1 to 2 Weeks
RSV is the virus most commonly behind bronchiolitis, an infection of the small airways in the lungs. It starts out looking exactly like a cold for the first few days: runny nose, stuffy nose, cough, and sometimes a slight fever. The difference shows up around days 3 to 5, when some babies develop wheezing and visibly harder breathing.
That labored breathing phase can last a week or more. In total, bronchiolitis symptoms persist for 1 to 2 weeks, though they occasionally stretch longer. The breathing difficulty is what makes RSV more concerning than a regular cold, especially in babies under 6 months. If your baby’s nostrils are flaring, their ribs are pulling in with each breath, or they’re breathing very fast, that warrants immediate medical attention.
Stomach Bugs: 1 to 10 Days
Viral gastroenteritis, the classic stomach bug, has two phases that resolve on very different timelines. Vomiting tends to settle quickly, often within 1 to 3 days. Diarrhea, however, can drag on for up to 10 days. This gap surprises a lot of parents who assume the illness is over once the vomiting stops.
The biggest risk with stomach bugs in babies isn’t the virus itself but dehydration. Babies lose fluids fast, and they can’t tell you they’re thirsty. Watch for fewer wet diapers (fewer than 6 in 24 hours for an infant), a dry mouth, crying without tears, or unusual sleepiness. Small, frequent feedings are more effective than large ones when your baby is vomiting.
Ear Infections: 3 to 7 Days
Ear infections often follow a cold, showing up just when you thought your baby was getting better. The good news is they frequently resolve on their own in about three days. Many pediatricians will recommend a “watch and wait” approach for babies over 6 months with mild symptoms, since antibiotics aren’t always necessary.
When antibiotics are prescribed, the course typically runs about a week. Most babies start feeling noticeably better within 2 to 3 days of starting the medication, even though they need to finish the full course. Tugging at the ear, increased fussiness (especially when lying down), and trouble sleeping are the hallmarks of an ear infection in a baby who can’t yet point to the pain.
Croup: 3 to 7 Days
Croup produces that distinctive barking, seal-like cough that tends to show up suddenly at night. Most children feel better within 3 to 7 days. The pattern with croup is that nights are significantly worse than days. Your baby may seem almost fine during the afternoon and then develop harsh coughing and noisy breathing after bedtime. Cool night air or sitting in a steamy bathroom can help ease the airway during these episodes.
Flu: About a Week
Most babies and children recover from the flu within a week, though it hits harder and faster than a cold. Fevers can spike to 103°F to 105°F, and babies tend to be much more miserable overall, with body aches, fatigue, and poor feeding. The fever typically breaks within the first 3 to 5 days, with energy and appetite gradually returning over the rest of the week.
Hand, Foot, and Mouth Disease: 7 to 10 Days
This one looks alarming but is generally mild. Most children recover in 7 to 10 days. The illness starts with a fever, sore throat, and general fussiness, followed a day or two later by small blisters on the hands, feet, and inside the mouth. The mouth sores are often the worst part because they make eating and drinking painful. Cold foods and fluids can help your baby stay hydrated through the uncomfortable days.
Why the Cough Sticks Around
One of the most common reasons parents think their baby is “still sick” is a lingering cough that hangs on well after the actual infection has cleared. Post-viral coughs are extremely common at any age and can persist for 3 to 8 weeks after the other symptoms are gone. The cough itself isn’t a sign of ongoing infection. It’s the airways recovering from inflammation, and it resolves on its own. A cough lasting beyond 8 weeks, though, is worth bringing up with your pediatrician.
When Your Baby Is Still Contagious
Your baby can spread a virus before, during, and even after visible symptoms. For respiratory viruses, contagiousness drops significantly once symptoms are improving and your baby has been fever-free (without medication) for at least 24 hours. Even then, the CDC notes that taking precautions for an additional 5 days helps reduce the remaining risk, since the body can still shed virus during that window.
For stomach bugs, babies remain contagious for several days after diarrhea stops. Hand-washing after diaper changes is the single most effective way to keep the rest of the household from catching it.
Fever Thresholds by Age
How serious a fever is depends heavily on your baby’s age. For babies 8 to 60 days old, the American Academy of Pediatrics flags any temperature at or above 100.4°F (38°C) as requiring medical evaluation, even if the baby looks fine otherwise. That threshold exists because very young infants can have serious infections without showing many outward signs. For older babies and toddlers, fever alone is less concerning than how the baby is acting. A baby with a 102°F fever who is still making eye contact, taking fluids, and having wet diapers is in a very different situation than one who is limp, unresponsive, or refusing to drink.