Scientists also found many were contaminated with salmonella.
Reusable plastic shopping bags have become increasingly popular in Britain thanks to supermarkets and other retailers giving out millions of free ones to shoppers in the last three years.
It is estimated that there are “hundreds of millions” of bags for life in use in Britain, according to sources within Wrap, the Government’s anti-waste watchdog. Because the vast majority of people do not wash their bags after each shopping trip, they could be putting themselves at risk.
The tests were undertaken by the University of Arizona, whose researchers stopped a total of 84 shoppers to check the state of their bags.
The researchers warned the levels of bacteria they found were high enough to cause a wide range of serious health problems and even death.
Children may be in the greatest danger, they added, as they are particularly vulnerable to the effects of organisms such as E.coli.
Many of the bags for life are made from jute or woven polypropylene, helping to reduce the amount of so-called “virgin plastic” used in carrier bags by 40 per cent in just the last three years.
But while they are better for the environment, the new research suggests they could be harmful to health if not cleaned regularly.
