People with lung diseases have bad breath, according to scientists in the United States.
A simple test for lung disease would help doctors and patients
Researchers at the University of Virginia say people with conditions like asthma and cystic fibrosis have highly acidic breath.
What's more, the acidity of their breath rises depending on how severe their condition is.
Writing in the European Respiratory Journal, they said a simple breath test could help doctors spot these diseases.
They said doctors should be able to distinguish between healthy patients and those with lung diseases quite easily.
This is because healthy people have breath which is slightly alkaline.
The researchers said the acidic breath associated with people with lung diseases may be caused by the overproduction of acids in the lung.
They believe this overproduction may even cause some of the symptoms associated with these diseases.
Dr John Hunt and colleagues said breath tests were a simple and reliable way of detecting lung diseases.
They asked 100 healthy patients to breathe into a disposable breathalyser.
The patients provided four samples a day for seven consecutive days.
This meant the researchers could measure the pH levels or acidity of over 900 breath samples.
They found that their pH levels remained relatively stable and slightly alkaline.
This is in contrast to people with lung diseases whose readings fluctuate but remain acidic.
The researchers found that the breath test was more reliable than alternative approaches, such as taking saliva samples from patients' mouths.
They also found that breath tests were as accurate as taking samples from the back of patients' throats.
Writing in the European Respiratory Journal, they said the procedure was "extremely simple to perform, inexpensive and robust".
In addition, they have shown that pH levels rise if patients receive proper treatment.
A simple test which reliably measures pH levels could transform the way these patients are diagnosed and monitored.
At the moment, UK doctors use spirometers to diagnose lung diseases. These machines measure the capacity and efficiency of the lungs by getting patients to exhale into them.
However, a recent study found that just 60% of NHS GPs have access to this equipment.