RSV in babies typically starts looking like an ordinary cold, with a runny nose, sneezing, and a mild cough. What sets it apart is how it can shift over the next few days, moving from the nose and throat down into the smaller airways of the lungs, where it causes visible changes in how your baby breathes, eats, and behaves. Knowing what to watch for at each stage helps you tell the difference between a cold that’s running its course and an infection that needs medical attention.
The First Few Days: Cold Symptoms
RSV almost always begins with upper respiratory symptoms that look identical to a regular cold. You’ll notice a runny nose, some congestion, sneezing, and possibly a cough that sounds dry at first. Your baby may seem a little fussy and have a hoarse cry. Some babies develop a low-grade fever (100.4°F or higher), but many infants with RSV never run a fever at all, which can be misleading if you’re using temperature as your main gauge of illness.
During this early phase, your baby may start eating or drinking less than usual. This is partly because congestion makes it harder to breathe through the nose while nursing or taking a bottle. For the first two to three days, RSV can genuinely look like nothing more than a head cold.
When It Moves to the Lungs
The hallmark of RSV is what happens around days three through five. The virus attacks the lining of the tiny airways (bronchioles) deep in the lungs. Damaged cells slough off and mix with mucus, plugging those narrow passages. In a baby, these airways are already very small, so even a small amount of swelling and mucus can significantly restrict airflow. This is called bronchiolitis, and it’s the point where RSV stops looking like a cold.
You’ll hear it before you see it in many cases. The dry cough becomes wet and persistent, and you may notice a wheezing sound, a high-pitched whistle when your baby breathes out. Some babies make a rhythmic grunting noise with each exhale, which is the body’s attempt to keep the small airways open. These sounds are distinct from the snuffly, nose-congested noises of a regular cold.
Visible Breathing Changes to Watch For
The most important thing to look for with RSV is how your baby’s body moves while breathing. When a baby is working harder than normal to get air in and out, you can see it in several specific places.
- Rib retractions: The skin pulls inward between the ribs or just below the rib cage each time your baby inhales. You may see shadows or indentations appearing and disappearing with each breath. Sometimes the tugging happens at the base of the throat, just above the collarbone.
- Nasal flaring: Your baby’s nostrils visibly spread wider with each breath. This is the body trying to pull in more air.
- Head bobbing: In younger infants, the head may rock forward slightly with each breath, a sign that the neck and chest muscles are straining.
- Belly breathing: The stomach pushes out noticeably with each inhale as the diaphragm works overtime. Some pulling inward of the belly during exhale may also be visible.
- Fast breathing: You can count your baby’s breaths by watching the chest rise. Breathing that looks rapid and shallow, especially when your baby is at rest or sleeping, is a red flag.
These signs are easier to spot when your baby is undressed or in just a diaper. If you’re unsure, lift the shirt and watch the chest and belly for 30 seconds. In normal breathing, the chest rises gently and symmetrically without visible pulling or straining anywhere.
Behavioral Signs in Babies Under 6 Months
Very young infants often show RSV differently than older babies. Rather than dramatic coughing or wheezing, you may notice quieter but equally important changes. The CDC lists irritability, decreased activity, and reduced feeding as key symptoms in babies under six months. Your baby may seem unusually sleepy or hard to wake, or swing between lethargy and intense fussiness that’s difficult to soothe.
Feeding becomes a reliable early indicator. A baby who is breathing fast simply cannot coordinate sucking, swallowing, and breathing at the same time. You may notice your baby pulling off the breast or bottle repeatedly, taking much smaller amounts than usual, or refusing to eat altogether. If your baby is producing noticeably fewer wet diapers than normal, that signals dehydration from reduced intake and needs prompt attention.
One symptom unique to young infants is apnea: pauses in breathing lasting longer than 10 seconds. You might notice your baby simply stop breathing briefly, sometimes with a slight color change around the lips or face, before starting again. This can happen even before the cough and wheezing develop, which makes it particularly alarming because it may appear before RSV is on your radar.
How RSV Differs From a Regular Cold
The early stages of RSV and a common cold are essentially indistinguishable. Both cause runny nose, congestion, sneezing, and mild fussiness. The key difference is trajectory. A typical cold stays in the upper airways and gradually improves over a week or so. RSV can descend into the lower airways and get noticeably worse around days three to five before it starts to improve.
Specific signs that suggest RSV has progressed beyond a cold include wheezing, visible rib retractions, nasal flaring, grunting, and any change in your baby’s skin color. A cold might make your baby congested and cranky, but it won’t typically cause the labored, whole-body breathing effort that bronchiolitis produces. If your baby’s cough is getting worse rather than better after several days, and you can see the physical strain of breathing, that’s the clearest signal you’re dealing with something more than a cold.
Signs That Need Immediate Attention
Most RSV cases are mild and resolve on their own with supportive care. But certain signs indicate your baby is struggling to get enough oxygen and needs evaluation quickly. These include significant difficulty breathing with visible flaring, retractions, or grunting; any color change in the skin, lips, or nailbeds (bluish or grayish tint); marked lethargy or difficulty waking your baby; and a significant drop in feeding or wet diapers.
Brief dips in oxygen levels can happen normally during illness and don’t always require emergency care. What matters is whether your baby recovers quickly or stays in distress. Sustained labored breathing, persistent irritability or lethargy, and an overall appearance of “just not right” are the patterns that warrant a trip to the emergency room. Babies who are hospitalized for RSV typically improve within a few days with oxygen support and help staying hydrated.
Prevention for Infants
An RSV antibody product (nirsevimab) is now recommended for infants younger than 8 months entering their first RSV season, which runs roughly October through March in most of the U.S. It’s a single injection, not a vaccine your baby’s immune system has to build a response to. Instead, it provides ready-made antibodies that offer protection right away.
Babies born during RSV season should ideally receive the injection within a week of birth, during the birth hospitalization. If the mother received an RSV vaccine during pregnancy at least 14 days before delivery, the infant generally does not need the antibody product, because protective antibodies were already passed through the placenta. For higher-risk children between 8 and 19 months old, including those with chronic lung disease, severe immune compromise, or cystic fibrosis with significant lung involvement, a second-season dose is recommended.