Professor Martyn Partridge, chief medical adviser to Asthma UK, said it had previously been difficult to show that smoking causes asthma as it only needed a few patients with lung disease to be wrongly classified as having asthma to skew the results.

BBC: Women seem to be more at risk

The search is difficult because doctors, scientists and patients aren't used to thinking of rheumatoid arthritis, asthma and Alzheimer's disease as having the same root cause.

FORBES: Magazine Article

These cause all the features of asthma, including swelling and narrowing of the bronchi and secretion of thick mucus which make it difficult for patients to breathe.

BBC: Asthma vaccine hope