RSV starts out looking exactly like a common cold, with a runny nose, cough, and mild fever. The difference is what happens next: over days 3 through 5, RSV can move into the lower airways and cause breathing difficulties that a regular cold does not. Knowing what to watch for during that window is the key to catching RSV early.
Early Symptoms That Look Like a Cold
In the first day or two, RSV is nearly impossible to distinguish from any other viral cold. Your baby may have a fever (100.4°F or higher), a runny nose, sneezing, congestion, and a cough that sounds either dry or wet. You might also notice fussiness, poor feeding, or a hoarse-sounding cry. These are all upper respiratory symptoms, meaning the virus is still in the nose and throat.
At this stage, there’s no single sign that points to RSV over another virus. The real question isn’t whether your baby has RSV specifically. It’s whether the illness is staying in the upper airways or moving deeper into the lungs. That shift typically happens around day 3 and is where RSV becomes a concern.
When Symptoms Move to the Lungs
RSV becomes more serious when it causes bronchiolitis, an infection of the small airways in the lungs. Symptoms are usually at their worst between days 3 and 5 of the illness and generally last 7 to 14 days total. The signs that the infection has moved lower are distinct from a regular cold, and they center on how your baby is breathing.
Watch for these changes:
- Fast breathing. Count your baby’s breaths for a full minute. Newborns normally breathe 30 to 60 times per minute, but rapid, shallow breathing beyond their baseline is a red flag.
- Nasal flaring. The nostrils visibly widen with each breath as your baby works harder to pull in air.
- Head bobbing. Your baby’s head may nod forward with each breath, a sign they’re using extra effort.
- Wheezing. A high-pitched whistling sound, especially when breathing out, means the small airways are narrowed or swollen.
- Grunting. A rhythmic grunting noise with each exhale means your baby is trying to keep air in the lungs longer.
- Belly breathing. Instead of the chest rising smoothly, you’ll see the belly push out with each breath while the area between the ribs or just below the neck pulls inward.
How to Spot Chest Retractions
Retractions are one of the most important signs to recognize. When your baby inhales, watch the rib cage closely. If you see the skin pulling inward between the ribs or forming an upside-down “V” shape under the neck, your baby is using muscles they don’t normally need in order to breathe. This is called a chest wall retraction, and it means the lungs are struggling to expand against swollen airways. Retractions are not part of a normal cold and signal that your baby needs medical attention.
Feeding Changes and Dehydration
Babies with RSV often lose their appetite. A congested nose makes it hard to breathe and eat at the same time, so your baby may pull away from the breast or bottle after just a few sucks. This is one of the earliest practical clues that something is more than a mild cold, especially if your baby was eating normally just a day earlier.
The bigger risk is dehydration. A baby who isn’t drinking enough fluids can become dehydrated quickly. Look for fewer wet diapers than usual (fewer than six in 24 hours for an infant), a dry mouth, no tears when crying, or unusual sleepiness. If your baby is consistently refusing feeds or showing signs of dehydration, that warrants a call to your pediatrician even if breathing looks fine.
Breathing Pauses in Very Young Infants
Babies under two months old can show a different, more alarming symptom: brief pauses in breathing, called apnea. Instead of the wheezing and coughing pattern seen in older babies, a very young infant with RSV may simply stop breathing for several seconds at a time. This can happen before other respiratory symptoms become obvious, making it easy to miss if you’re expecting a cough-first pattern. Any noticeable pause in a newborn’s breathing is an emergency.
Which Babies Are at Higher Risk
Almost all children catch RSV before age two, and most recover on their own. But certain babies are more likely to develop severe illness. The highest-risk groups include babies born premature, infants with chronic lung disease who needed oxygen or other respiratory support in recent months, babies with significant congenital heart disease, and children with weakened immune systems or cystic fibrosis. American Indian and Alaska Native children also face a higher rate of severe RSV-related illness.
Age alone is a major factor. Babies under six months old, and especially those under two months, are more vulnerable simply because their airways are tiny and their immune systems are still developing. A full-term, otherwise healthy three-month-old can still end up needing medical care for RSV, so risk factors are worth knowing but shouldn’t be your only guide.
How RSV Is Diagnosed
If you bring your baby in with breathing symptoms, the doctor may test for RSV with a nasal swab. Two types of tests are commonly used. A rapid antigen test gives results quickly, often within the appointment, but is somewhat less accurate. A PCR test (the same technology used for COVID testing) is highly sensitive and more reliable, though results may take longer. In many cases, especially during RSV season, a doctor may diagnose based on symptoms and a physical exam alone, since treatment focuses on managing breathing rather than on which specific virus is responsible.
What the Illness Looks Like Day by Day
Days 1 and 2 typically look like a standard cold: runny nose, mild cough, possibly a low fever. Your baby may seem a little off but not alarming. Days 3 through 5 are the critical window. This is when the virus can descend into the lungs and breathing symptoms appear or worsen. If your baby is going to need medical help, it’s most likely during this stretch. After day 5, most babies begin to slowly improve, though the cough and congestion can linger for one to two weeks.
The tricky part is that RSV may not seem severe at the start. A baby who looked fine on Monday can be breathing noticeably harder by Wednesday. This is why monitoring matters more than the initial impression. Check on your baby’s breathing several times a day during the first week of any cold-like illness, especially at night and during feeds when breathing difficulty tends to be more visible.
What to Watch For at Home
If your baby has cold symptoms, you don’t need to panic, but you do need to stay observant. Keep a mental checklist: Is the breathing getting faster? Can you see the ribs or neck pulling in? Is your baby eating at least half their normal amount? Are there enough wet diapers? Is your baby alert and responsive between bouts of coughing?
A baby who is breathing comfortably, eating reasonably well, and staying hydrated is likely managing the virus fine. A baby who is breathing hard, refusing feeds, becoming unusually limp or difficult to wake, or showing any color changes around the lips or fingertips (bluish or grayish tint) needs immediate medical evaluation. Trust the breathing. If it looks like work, it is.