We still do not know what causes some people to develop asthma. Research shows that a family history of asthma or allergies, a specific allergy in the child or cigarette smoking during pregnancy may increase the likelihood that a person will develop asthma early in life. One of the most common causes of asthma symptoms in children five years old and younger is a respiratory virus. Although both adults and children experience respiratory infections, children have more of them and some preschool children are plagued with viral infections. At least half of children with asthma show some sign of it before the age of five.
Viruses are the most common cause of acute asthma episodes in infants six months old or younger.
Infants and toddlers have much smaller bronchial tubes than older children and adults. In fact, these airways are so small that even small blockages caused by viral infections, tightened airways or mucous can make breathing extremely difficult for the child. Asthma symptoms can look like symptoms of other illnesses or diseases. Diagnosing asthma in very young children is difficult. Since they are not able to communicate, they cannot describe how they are feeling.