American researchers believe the answer to the age-old embarrassment could be charcoal. Their research revealed that an object called a Toot Trapper, a cushion covered in activated charcoal, reduced the smell of flatulence to almost unnoticeable levels.

The scientists from Minneapolis Veterans' Affairs Medical Centre fed 16 healthy people pinto beans and lactulose and waited for the results.

The beans, along with broccoli, cabbage, nuts, bread and beer, are difficult to digest and are well-known for producing hydrogen sulphide, the substance which puts the sting into flatulence. It was described as giving a rotten egg smell by the scientists while dimethyl, another gas isolated in tests, had a "sweet" bouquet.

It's all in the nose

The researchers selected two judges who had proved their ability to distinguish between the array of different gases through a blindfold test.

Broccoli produces hydrogen sulphide which puts the sting into rectal gas

Their job was to hold a syringe of gas three centimetres from their noses, slowly empty it and sniff. They had to rate the odour emitted on a scale of 0 (no odour) to 8 (very offensive).

Eight of the guinea pigs wore specially designed gas-tight pantaloons made of metallised nylon which prevented any smell leakage. A catheter was attached to the subjects' anus.

Some of the guinea pigs had a Toot Trapper placed in the pantaloons, others had a "placebo cushion" and some had no cushion at all.

Cruel myth

In addition to finding that the charcoal-coated cushions reduced the bad smell levels produced by hydrogen sulphide to almost nothing, the researchers put paid to a cruel myth.

They say it is not true that men produce more violent smells than women. In fact, it is the other way around, although men may emit a greater volume of bad odours.

The study of flatulence dates back to 1816, but it relates mostly to the gas produced, rather than its smell.