Bronchiolitis is a viral lung infection that causes inflammation in the smallest air passages in your lungs called bronchioles. Although it’s generally a childhood condition, bronchiolitis can also affect adults.

Inflammation of your bronchioles can cause a blockage of oxygen in your airways that leads to symptoms such as coughing or trouble breathing. Bronchiolitis generally causes mild illness, but serious cases can progress to lung failure.

Read on to learn more about bronchiolitis including symptoms, causes, and treatment options.

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Bronchiolitis is a viral infection that usually affects young children and infants. It causes inflammation of the smaller airways in the lungs. Illustration: Wenzdai Figueroa.

Bronchiolitis and bronchitis are both viral infections of your lungs, but they affect different structures.

When you breathe in air, it travels from your windpipe to the main passage in each of your lungs called the primary bronchi. From there, air passes through smaller bronchi and then to even smaller passages called bronchioles.

Bronchitis is an infection of your bronchi. Bronchiolitis is an infection of the smaller bronchioles.

There are two main types of bronchiolitis:

Viral bronchiolitis

Most cases of viral bronchiolitis are due to respiratory syncytial virus (RSV). Viral outbreaks occur every autumn and winter and primarily affect children younger than 2 years old, with infants under 6 months at the highest risk of severe illness.

Bronchiolitis obliterans

Bronchiolitis obliterans, or popcorn lung, is a rare and dangerous condition seen in adults caused by severe lung infections or chronic exposure to toxins in the air such as formaldehyde, ammonia, or metal oxide fumes. This disease causes scarring in the bronchioles. Scarring blocks air passages and causes airway obstruction that can’t be reversed.

According to the American Lung Association, the initial symptoms of bronchiolitis often mimic common cold symptoms. They may include:

Over the next several days, symptoms often get worse before gradually getting better. They might include:

According to the National Health Service, symptoms are generally worse between days 3 to 5.

It’s a good idea to contact your child’s doctor if they:

  • are breathing faster than usual
  • having difficulty breathing
  • have significant appetite loss
  • have a persistent fever above 100.4°F (38°C)
  • are very tired or irritable
  • haven’t had a wet diaper in 12 hours

It’s particularly important to seek medical attention if your infant is less than 12 weeks old or has a heart or lung condition.

Bronchiolitis obliterans symptoms tend to flare up when exercising or doing manual labor. Symptoms generally develop over weeks to months and most commonly include:

  • wheezing
  • dry cough
  • shortness of breath
  • fatigue
  • eye, skin, mouth, or nose irritation, if caused by chemical exposure
When to seek emergency medical attention

If your child experiences any of the following, you should call 911 or take them to the nearest emergency room:

  • extremely fast breathing
  • an inability to wake or to stay awake
  • skin, lips, nail beds, or tongue that turn pale or blue
  • long pauses in their breathing or regular short pauses
  • signs of difficulty breathing, such as grunting or visible rise and fall of their stomach
  • visible muscles under their ribs while breathing
  • nasal flaring while breathing

There are different causes of viral bronchiolitis and bronchiolitis obliterans.

Causes of viral bronchiolitis

Viruses that enter and infect the respiratory tract cause viral bronchiolitis. Viruses are microscopic organisms that can reproduce rapidly and challenge the immune system. The following are common types of viral infections that may cause bronchiolitis.

Respiratory syncytial virus (RSV)

RSV is the most common cause of bronchiolitis. RSV can affect people of all ages but is most likely to cause serious illness in children under 2 years old or in older adults with weakened immune systems. Most babies get RSV infections at least once by the time they turn 2 years old.

About 11 to 15 percent of infants experience bronchiolitis before they turn 1 year old, and about 1 in 200 children under 2 years old are hospitalized with bronchiolitis.


Adenoviruses target mucous membranes. They cause about 5 to 10 percent of respiratory tract infections in children and 1 to 7 percent in adults.

Influenza viruses

These viruses cause inflammation in the lungs, nose, and throat. Influenza affects both adults and children. It’s especially dangerous for babies who don’t have strong immune systems.

Causes of bronchiolitis obliterans

This rare condition sometimes occurs for no known reason. Severe cases can lead to death if they’re left untreated. A few causes have been identified and include:

  • complication from lung or stem cell transplant
  • fumes from e-cigarette smoke
  • fumes from chemicals like ammonia, bleach, and chlorine
  • respiratory infections
  • adverse reactions to medications

Viral bronchiolitis most commonly affects children under 2 years old. A few risk factors for viral bronchiolitis in babies and young children are:

  • not being breastfed
  • being born prematurely or born with a heart or lung condition
  • having a suppressed immune system
  • being exposed to cigarette smoke
  • being in crowded places where the virus is present, like daycare centers

Common risk factors for bronchiolitis obliterans in adults are:

  • working conditions that expose you to dangerous chemicals
  • having had a heart, lung, or bone marrow transplant
  • smoking tobacco containing nicotine
  • having an autoimmune connective tissue disease

There are several ways to diagnose both types of bronchiolitis:

  • physical exam and medical history evaluation, including potential environmental exposures
  • imaging testing, including chest X-rays or a CT scan
  • spirometry, which measures how much and how quickly you take in air with each breath
  • arterial blood gas tests measure how much oxygen and carbon dioxide are in your blood

Samples of mucus or nasal discharge can help your doctor diagnose the type of virus causing the infection. This testing method is common with babies and small children.

Viral bronchiolitis requires different treatments than bronchiolitis obliterans.

Treatments for viral bronchiolitis

Many cases of viral bronchiolitis are mild and clear up without treatment. For more severe cases in infants, hospitalization may be necessary. A hospital can provide oxygen and intravenous fluid treatments. Antibiotic medications don’t work against viruses, but some medications can help open your baby’s airways.

Treatments for bronchiolitis obliterans

There’s currently no cure for the scarring of bronchiolitis obliterans. Treatment options include:

Home care

Recovery from both conditions requires extra rest and increased fluid intake. Keeping the air in your home clear of smoke and chemicals is very important. A humidifier to keep the air moist may also help.

The best way to prevent viral bronchiolitis is to minimize contact with viruses that causes the illness. Inhaling smoke can also put your child at an elevated risk of respiratory infections.

Here are ways to minimize the chances of your child developing bronchiolitis:

  • Keep them away from people who are sick with infectious diseases, especially when your child is younger than 2 months.
  • Regularly disinfect surfaces and toys your child often comes into contact with.
  • Fully wash and dry your child’s utensils.
  • Wash your child’s hands frequently, especially before and after feeding and after they touch their nose or mouth.
  • Keep your child away from secondhand smoke.

The cause of bronchiolitis obliterans isn’t always known, but avoiding exposure to toxic chemicals in the air and taking steps to avoid respiratory illness like washing your hands regularly and avoiding people who are sick may help reduce your chances of developing it.

Children and babies with mild viral bronchiolitis usually recover within 2 to 3 weeks with prompt, proper treatment. More serious cases of bronchiolitis may require hospitalization.

The outlook for someone with bronchiolitis obliterans depends on when the condition was diagnosed and how far it has progressed. But treatment can help manage symptoms.