Bronchiolitis is a lung infection caused by a virus, most commonly affecting young children and infants, that causes inflammation and blockage of the bronchioles in the lungs. It often flares up in the winter with initial symptoms similar to a common cold but then progresses to coughing, wheezing and sometimes difficulty breathing.

Acute bronchiolitis is common in children under 2 years old, especially very young children who are still breastfeeding. The disease has many different levels, it can be mild and transient, the child will recover after a few days or it can be very severe, causing respiratory failure and death.

Bronchiolitis is an acute bacterial infection of the small and terminal bronchi called bronchioles. This condition causes obstruction of the bronchioles. When the bronchioles are infected, they become inflamed, swollen, and edematous, secreting a lot of mucus, causing the child's airways to narrow, making it difficult to breathe, and even causing obstruction due to mucus leading to collapsed lungs.