Scientists have known for decades that individuals who have allergies and asthma are more reactive to irritants such as tobacco smoke and fragrances, but had no idea why, until recently.

Researchers at John Hopkins discovered that a small, powerful molecule of the nervous system, called nerve growth factor (NGF), may play a significant role in asthma, hay fever, and other allergic diseases.

NGF helps maintain certain nerve cells and prods other nerve cells to grow and communicate with others. For this reason, it was being tested as a treatment for nerve and brain disorders. It was during these tests that researchers discovered NGF also played a role in allergic reactions.

The studies revealed a significant increase in NGF levels when people, who had reported chronic symptoms of allergic rhinitis (hay fever), were exposed to ragweed and grass pollen. When inflammation is present, the cells in the allergic reaction produce NGF. During a reaction these cells secrete and release NGF in large quantities into the upper airways.

“Hay fever and asthma now seem to derive from events not only in the respiratory system, but also from a nervous system that is over reacting to stimuli,” Vassilis Koliatsos, M.D., an associate professor of pathology, neurology and neuroscience at the Johns Hopkins School of Medicine, told reporters.

Alvin Sanico, M.D., lead author of the study and an assistant professor of medicine at Hopkins, added this discovery can bridge the two major features of allergic airway disease: inflammation and hyper-responsiveness to irritants. He also stated that more studies were currently under way to further understand this new facet of allergic airway disease in humans.