Forget bigger salaries, company cars and Christmas bonuses. Scientists have discovered a simple way to improve a worker's motivation – change the office carpet.

Odours given off by old carpets can be so subconsciously pungent that they can affect productivity, a study says.

The findings were made with the help of a 20-year-old tufted bouclé carpet that the scientists took from an office with a record of poor air quality and complaints from occupants. Volunteers spent 4.5-hour periods carrying out simple office tasks while sections of the carpet, which had never been cleaned, were hung out of sight and its odours wafted in.

One experiment resulted in 30 women, in groups of six, producing a clear and unequivocal downturn in productivity, according to Professor Ole Fanger, of the International Centre for Indoor Environment and Energy at the Technical University of Denmark. Prof Fanger invented the 'olf' unit, defined as the amount of body odour given off by a standard European person after a shower.

An average smoker emits six olfs when not smoking and a trained athlete exercising vigorously emits 20. The carpet raised the office level to 0.2 per square metre, enough to cause headaches, dizziness and nausea among the volunteers.