We should stop washing our hands as often to protect ourselves against allergies and food intolerances, experts suggest.
This would encourage helpful bacteria - essential for regulating the immune system - into the body.
American scientists say these microbes are vanishing from our guts because of a huge reduction in the amount of fibre in our diets.
Bacteria live primarily on fibre and people today eat just a tenth of the roughage consumed in hunter-gatherer societies.
Widespread antibiotic use, caesarean sections and less-frequent breastfeeding in industrialised nations could also account for the depletion of intestinal microbes.
Many experts believe the fall in microbes has fuelled a rise in allergies and food intolerances.