Health

Rubbing salt in 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 far more difficult for the microbes to extract water from the solution without using a lot more energy. As a result, the bacteria become placid and 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.

Blood is 83 per cent water. Because salt is hygroscopic, it absorbs water, accelerating the tendency for blood to clot and drying the wound. This helps deny microorganisms a favourable habitat. Saline solutions do generate osmotic pressure – it forces water out of microbes to equalise the salt concentration across their cell membranes. This can kill them, so salt acts as a disinfectant.

The stinging of the wound signals that salt does cause injury to the body. But in the absence of a better option at the time, killing a few healthy skin cells was deemed acceptable collateral damage when the alternative may have been a serious infection or possible death.