Britons are likely to be sleeping under duvets which are riddled with dust mites and dead skin, research shows.
20,000 of these minuscule monsters could be in your duvet
Tests carried out on 10 duvets at the University of Worcester found they held up to 20,000 live house dust mites.
And a survey also revealed two-in-five Britons admitted to not washing duvets every six months.
The worst case was a duvet that had not been washed for 11 years and contained 45g of debris including skin scales and house dust mite faeces.
"This content has serious implications for health as the contaminants can cause symptoms of asthma, rhinitis and conjunctivitis and irritate existing cases of eczema," said Professor Jean Emberlin, director of the university's national pollen and aerobiology research centre, which carried out the research.
Seven of the 10 duvets tested had never been washed - two of which were more than a decade old. Most were synthetic and one was filled with feathers.
An additional survey of 1,000 people showed that 41% didn't wash their duvet every six months.
Men appeared to be cleaner, with 36% admitting they didn't clean their duvet every six months, compared to 51% of women.
The research project was commissioned by Hotpoint Aqualtis.