You cannot be "too clean", millennials are being told, as public health experts attempt to debunk myths around hygiene. The Royal Society for Public Health (RSPH) said incorrect theories which became popular in the 1990s were fuelling confusion and unhygienic habits among subsequent generations.

And they called for lessons on cleanliness to be included in the national curriculum

The warning comes after organisers of Glastonbury urged festival goers to opt for “strip washes” with a flannel and soap, instead of a shower, in order to help the environment.

The “hygiene hypothesis” which became widely publicised in the 1990s argued that rising rates of allergies were being caused by "overcleanliness," suggesting children should be exposed to a wide range of potentially harmful microbes.

But experts from the Royal Society today stressed this is not the case.

They said people need diverse exposure to microbes that are mostly harmless - such as those children can find playing outdoors - but should remain vigilent about hygiene in the home.

The research found that one in six men thought there was low or no risk associated with not washing their hands after using the toilet, while one in 12 saw no need to wash their hands after handling raw meat. Around half as many women had such views.