US scientists say they have hard evidence to show that certain emotions can cause flare ups of asthma.
The researchers found two brain regions were important
The University of Wisconsin-Madison team discovered activity in brain areas linking the two in asthmatics who read emotive words.
One brain region has a role in obtaining information about disease symptoms while another processes emotions.
Their findings appear in Proceedings of the National Academy of Sciences.
Dr Richard Davidson and his team asked six patients with mild asthma to take part in their experiments.
Each was shown three different categories of words - asthma-related words such as "wheeze", negative but non-asthma-related words such as "loneliness" and neutral words such as "curtains".
At the same time, the volunteers were given known triggers of asthma to inhale, such as ragweed or dust-mite extract.
Meanwhile, their brain responses were monitored using functional magnetic resonance imaging.
Two brain regions - the anterior cingulate cortex and the insula - showed increased activity when the asthma-related words were heard compared with the other word types.
Furthermore, the increased brain activity was linked to body function signals from the inhaled allergens.
The researchers said that because of the small number of people studied their findings would need to be repeated and that it was likely that other brain areas are also involved in the relationship between emotions and asthma.
However, they said: "These brain areas may be hyperresponsive to disease-specific emotions."
In turn, this might contribute to problems that worsen asthma, such as inflammation, they said.
Chairman of the British Lung Foundation Dr Mark Britton said: "These are interesting findings.
"We have always known that asthma and a patient's personality and emotions are very intrinsically bound up with each other.
"We do need further research into this."
For example, whether increasing the dose of medication might help to cover tough emotional times.
He said it was often useful to counsel a patient that their asthma may get worse when they are stressed.
"If you have insight into your disease you are much better able to cope with it."
Dr Lyn Smurthwaite of Asthma UK said: "It's well known that stress aggravates asthma and that asthma aggravates stress.
"Our research shows that 69% of people with asthma say stress triggers their symptoms, and this study shows an actual link between the parts of the brain processing emotion and physiological asthma symptoms."