A United States federal court jury has awarded $7.2 million in damages to a man who developed a lung disease from flavoured microwave popcorn.

Jurors agreed with the claims by Wayne Watson that the popcorn manufacturer and the supermarket chain that sold it were negligent by not warning on labels that the butter flavouring diacetyl was dangerous.

Mr Watson, 59, was diagnosed with the disease in 2007 after years of inhaling the smell of artificial butter on the popcorn he said he ate daily.

The court heard the chronic condition known as popcorn lung is a form of obstructive lung disease that makes it difficult for air to flow out of the lungs and is irreversible.

Mr Watson's lawyer, Kenneth McClain, said since 2004 he has represented microwave popcorn and flavouring workers across the US who have been awarded large damages.

He said Dr Cecile Rose, a witness for Mr Watson, made the connection between his disease - bronchiolitis obliterans - and diacetyl when she asked him if he had been around large quantities of microwave popcorn.

She had been a consultant to the flavourings industry and had seen the same disease that Mr Watson had among workers exposed to the chemical.

The verdict was the latest in a line of cases in the past 15 years, starting with workers in popcorn plants where diacetyl was an ingredient, that has linked the chemical to health problems.

Jurors found Gilster-Mary Lee Corp, the private-labelling manufacturer of the popcorn, liable for 80 per cent of the $7,217,961 damages and the King Soopers supermarket chain and its parent, Kroger Co, liable for 20 per cent.

A lawyer for the defendants had told jurors Mr Watson's health problems were from his years of using dangerous chemicals as a carpet cleaner.

A spokeswoman for King Soopers and Kroger said the companies intended to appeal against the decision.

An attorney for Gilster-Mary Lee was not available for comment.

Reuters