Researchers at the University of Westminster found bacteria increases by up to 600 per cent when hot air hand dryers are used in public lavatories.
The analysis found towels were successful in reducing the bacteria count.
In all locations 63 per cent of the dryers blew out gut bacteria, which indicates faecal contamination; 80 per cent of the dryers in hospitals blew out bacteria which can cause broncho-pneumonia. Air inlets and nozzles showed 'considerable bacterial contamination'.
Keith Redway, a microbiologist who carried out the analyses, said: 'We found bacteria which offer a threat to people who are impaired in some other way, people who have more chance of picking something up.'
The research has the support of the Association of Soft Tissue Manufacturers, but the researchers emphasise that their work is impartial.