An international study in hospitals established that modern dryers create an aerosol effect, blasting E. Coli as well as traces of faeces and the bacteria responsible for septicaemia onto surfaces.
While the devices can often be activated without being touched, which is supposed to improve hygiene, they are problematic because people fail to properly wash their hands, the experts said.
This leaves harmful bacteria on the surface of the skin ready to be blown around the room.
By contrast, paper towels absorb the bugs better, preventing other people from becoming exposed to them.
Published in the Journal of Hospital Infection, the study, the largest of its kind, was partly carried out at Leeds General Infirmary.
Department of Health guidance says air dryers should only be placed in public rather than clinical areas of the hospital, but only because of concerns around the noise.
The study authors wrote the rules on the use of jet dryers need to be strengthened on the in the light of the new evidence.
"The problem starts because some people do not wash their hands properly,” said Professor Mark Wilcox, who led the study at the University of Leeds.
"When people use a jet air dryer, the microbes get blown off and spread around the toilet room.
"In effect, the dryer creates an aerosol that contaminates the toilet room, including the dryer itself and potentially the sinks, floor and other surfaces, depending on the dryer design and where it is sited.
“If people touch those surfaces, they risk becoming contaminated by bacteria or viruses.”
The study looked at bacterial spread in a real world setting - in two toilets in each of three hospitals, which were in the UK, France and Italy.
Each of the toilets had paper towel dispensers and jet air dryers, but only one of these was in use on any given day.
On each day, over 12 weeks, levels of bacterial contamination in the toilets were measured, allowing comparisons to be made when either paper towels or jet air dryers were in use.
Samples were taken from the floors, air and surfaces in each of the toilets.
The main target bacteria were Enterobacteria including Escherichia coli or E.coli, which cause a wide range of infections including gastroenteritis, pneumonia and septicaemia, and enterococci - bacteria that can cause difficulty when treating infections.
They also looked for Staphylococcus aureus, which is responsible for a range of conditions, from minor skin and wound infections to life-threatening septicaemia.
Across the three hospitals, bacterial counts were significantly higher in the toilets on the days that jet air dryers were in use.
Professor Wilcox: "We found multiple examples of greater bacterial contamination on surfaces, including by faecal and antibiotic-resistant bacteria, when jet air dryers rather than paper towels were in use.”