Aston University academic highlights contamination risks of the reuseable bag

Reusing carrier bags for a diverse range of contents puts consumers at risk of bacterial contamination – that is the warning of Professor Anthony Hilton, Head of Biological and Biomedical Science at Aston University.  As a 5p charge is introduced for carrier bags in England, he claims that without understanding the need to restrict different bags for different uses, shoppers increase their chances of contamination from a range of bacteria.

The new 5p charge has seen a surge in supermarkets giving out ‘bags for life’ in the past few weeks. Whilst there is no dispute that there are huge environmental benefits to this, Professor Hilton warns of the unintended consequences of reusing plastic bags which the public should be aware of to minimise their risk of exposure to harmful bacteria.

Hilton said: “Reusing plastic bags is hugely beneficial to the environment but the public should be mindful of the ability of bacteria to contaminate and survive on bags for long periods of time. Bacteria can easily transfer from different types of reuseable bags to the hands and back again. What is more, using the same bag repeatedly for different purposes increases the risk of contaminating the bag with a whole host of harmful bacteria.”

Professor Hilton and his research team undertook a study of three different types of bag. They investigated the ability of bacteria to survive on the bag and also the ease of transfer of bacteria from the skin to the bag, and the bag to the skin. Laboratory experiments revealed that:

  • 1 million cells of Staphylococcus aureus, the bacteria commonly found on the hands but which can cause illness, when placed on the bag survived over 8 weeks and took 16 weeks to disappear completely
  • 1 million E. coli cells, known to cause diarrhoeal infection, survived 48 hours before becoming undetectable – enough time to cause illness
  • Up to 23% of bacteria on plastic bags could  be transferred in a single touch to hands

“We are not saying people shouldn’t adopt reusable shopping bags,” said Hilton. “What is important is that the public understand the potential health risks, and think about which bags they are using for which purpose. For example, carrying fresh meat brings with it known contamination risks and if you then use the same bag for carrying ready-to-eat foods such as cheese or bread there is the potential for cross-contamination. Likewise, if you carry sports shoes one day and then shopping the next.

“In our study, the handles of ‘in use’ bags were found to have bacteria typically found on the skin, however inside the bags, there was a much more diverse range of bacteria, some which are associated with human disease. Clearly the microbial community of the bag is representative of what is carried in it.”