Asthma patients who believe that a particular odor is harmful, even if it is not, have increased airway inflammation for at least 24 hours after exposure, a new research shows.

Researchers at the Monell Chemical Senses Center, U.S., said that the findings shed light on the psychological connections in health-related outcomes.

"Asthmatics often are anxious about scents and fragrances. When we expect that an odour is harmful, our bodies react as if that odour is indeed harmful," study lead author Cristina Jaen, a Monell physiologist, said in press release.

For the study, 17 individuals characterized as moderate asthmatics were exposed to the odor phenylethyl alcohol (PEA) for 15 minutes. Researchers explained that PEA is commonly described as rose-smelling and is regarded as a 'pure' odorant with no associated physiological irritant qualities.

Eight participants were told that the odor contained therapeutic properties and rest nine were told that it might cause mild respiratory problems.

Researchers told the participants to rate the sensory properties of the odor such as intensity, irritancy, and annoyance.

The team then collected the measures of lung function and airway inflammation before and immediately after exposure and again at two hours and 24 hours post-exposure.

Researchers found that the beliefs of the respondents about the odor, specifically whether it was potentially harmful or therapeutic, deeply impacted both their psychological and physiological responses to the smell.

Those who were told that the odor was harmful rated it as irritating and annoying as opposed to participants who thought it might be therapeutic.

Moreover, researchers found that airway inflammation increased immediately after odor exposure in subjects who believed that it might be harmful and remained elevated 24 hours later.

The study found no inflammation in people who were told the odor was therapeutic, even in people who described themselves as sensitive to perfumes and such.

"Introducing a negative bias led to a rapid change in airway inflammation," said senior author Pamela Dalton, a cognitive psychologist at Monell. "What really surprised us was that this response lasted for over 24 hours. The increased inflammation during this period likely makes asthmatics more sensitive to other triggers," Dalton said.