Bronchiolitis is most often caused by a virus, especially RSV, and usually starts after a cold-like illness or exposure to someone who is sick. If you’re wondering how a baby gets bronchiolitis or what may have led to your child’s symptoms, we can help you sort through the most likely causes and what to do next.
Share what happened before your child’s symptoms began, and get personalized guidance on common bronchiolitis causes in infants, babies, and toddlers.
If you searched "is bronchiolitis caused by a virus," the short answer is yes—most cases are. Bronchiolitis happens when a virus infects the small airways in the lungs, causing swelling and mucus buildup. The most common cause is respiratory syncytial virus, often called RSV, but other cold viruses can lead to bronchiolitis too. This is why symptoms often begin after a runny nose, cough, or recent exposure at daycare, school, or home.
RSV is the most common virus that causes bronchiolitis in babies and young children. Many parents searching for the RSV cause of bronchiolitis are seeing the most likely explanation.
Rhinovirus, human metapneumovirus, parainfluenza, influenza, and adenovirus can also cause bronchiolitis, especially during cold and flu season.
Bronchiolitis is contagious because the viruses that cause it spread through droplets, hands, shared surfaces, and close contact with someone who is sick.
A mild cold can move into the lower airways over several days. This is one of the most common ways bronchiolitis causes in infants begin.
Children in group settings are around more viruses, which can increase the chance of bronchiolitis after exposure to another child with cold symptoms.
Older siblings, parents, and caregivers can bring home viruses even before they realize they are sick, which is a common answer to how does a baby get bronchiolitis.
Any baby or young child can get bronchiolitis, but it is especially common in infants because their airways are smaller and can become blocked more easily by swelling and mucus. Premature babies, infants under 12 months, and children with certain heart, lung, or immune conditions may be more affected when they catch the viruses that lead to bronchiolitis.
If your child started with a runny nose, mild cough, or fever before breathing symptoms worsened, a viral cause is more likely.
Recent contact with a sibling, classmate, or caregiver who had cold symptoms can help explain what causes bronchiolitis in children.
Bronchiolitis is more common in fall, winter, and early spring, when RSV and other respiratory viruses spread more easily.
Bronchiolitis in babies is usually caused by a virus that infects the small airways in the lungs. RSV is the most common cause, but other respiratory viruses can cause it too.
Yes. Bronchiolitis is most often caused by a viral infection, not by bacteria. It commonly begins after a cold-like illness and can spread from person to person.
Respiratory syncytial virus, or RSV, is the virus most often linked to bronchiolitis. Many infants and toddlers get RSV at some point, and some develop bronchiolitis as a result.
A baby usually gets bronchiolitis by catching a virus from someone who is sick or from contaminated hands and surfaces. Exposure at home, daycare, or around siblings is common.
The viruses that cause bronchiolitis are contagious. That means the illness can spread through coughs, sneezes, close contact, and touching shared objects or surfaces.
In toddlers, bronchiolitis is also usually triggered by a viral infection, often after exposure in daycare, preschool, playgroups, or from family members with cold symptoms.
Answer a few questions about recent illness, exposures, and symptom timing to better understand the likely cause and the next steps to consider.
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