Most people give a bagged salad a quick rinse with tap water before they eat it, just to get rid of pesticides or bugs. But according to new research, washing a salad might be making you more likely to get ill, not less.

The Istituto Superiore di Sanità, the research arm of the Italian National Health Service, had researcher Dr Elisabetta Delibato deliberately spike lettuce with both salmonella and Yersinia enterocolitica – a bacteria that attacks the gut and can cause sepsis. The lettuce was then kept in a fridge at 4oC for a week and washed in both tap water and water containing chlorine. 

Dr Delibato found the washing does nothing to eradicate the bacteria. “The recent knowledge about vegetables, as a vehicle of foodborne illnesses, has led to increase the research on the persistence of different pathogenic microorganisms on leafy green vegetables. In this work we have demonstrated that salmonella and Y. enterocolitica could survive in fresh produce for all their shelf life without any substantial reduction of their microbial loads. 

Explaining how washing lettuce could actually make things even worse, she adds: ‘Washing has been identified as a potential pathway for dispersion of microorganisms from one site to another. removing the bacteria from initially localised contaminated parts and spread them to the rest of non- contaminated leafy green vegetables.”

However, there is currently no safer way to wash salad in a domestic kitchen. So despite this, the researchers still advise consumers to give their salad an extremely thorough wash (not just a quick rinse under the tap).