Wheezing in infancy and childhood is not a single disorder and is just as likely to be due to causes other than asthma.

In more than half of the children who wheeze within their first three years, the wheezing is transient and does not increase the risk of later asthma.

Wheezing that persists and is likely to develop into asthma can have an early or late onset.

Children with persistent wheezing are more likely than those with transient wheezing to have features of atopy and reduced lung function by the age of six years.

The earlier asthma symptoms such as persistent wheezing appear, the more severe the disease in later life and the greater the damage to the airways.

There is a clear association between parental asthma or atopy, persistent wheezing and asthma.

Exposure to tobacco smoke significantly increases the risk of wheezing in the first three years of life but not in later childhood.

Maternal smoking during pregnancy is a risk factor for transient wheezing and affects lung development.

There is a strong association between atopy, persistent wheezing and asthma, but the role of allergic sensitisation in the development of asthma is not yet clear.

Environmental conditions that increase the rate of bacterial and viral infections are risk factors for transient wheezing but may protect against persistent wheezing and asthma.

Children with frequent simple colds and other common childhood infections in infancy are less likely to develop persistent wheezing in later childhood.