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I realise that “rubbing salt into the wound” was a way of preventing infection. But how did it work?

• Applying salt to a wound creates a highly saline environment, one in which it is difficult for microbes to grow. The high concentration gradient between the salt solution and the fluid inside bacterial cells makes it hard for the microbes to extract water from the solution without using a lot of energy. As a result, the bacteria become dehydrated and cannot function normally or proliferate.

Concentrated sugar solutions also have a dehydrating effect. This accounts for the extended shelf life of chutneys and preserves, and explains why honey can be used on wound dressings and, ironically, on bee stings as an antiseptic.

Scott Somerville, Cleghorn, South Lanarkshire, UK