Have you washed your hands yet today? It is 10am and Lisa Ackerley, professorial fellow of the London-based Royal Society for Public Health, AKA the Hygiene Doctor, says she has already washed hers five times. (Well, she has been cleaning the toilet.) This would probably be seen as obsessive by the Fox news host Peter Hegseth, who this week declared he had not washed his once in 10 years. He “inoculates” himself, apparently. Hegseth has since claimed he was joking. But not many people have wanted to shake his hand on it.

What could be on a hand that has not been washed in a decade? “Hands are the most important vector of infectious diseases,” says Professor Val Curtis of the London School of Hygiene and Tropical Medicine, who lists salmonella, E coli and norovirus among the germs that “hitchhike on hands”.

‘It is antisocial not to wash hands.’ Photograph: Bix Burkhart/Getty Images

“If this guy goes to the toilet and wipes his bum, or doesn’t, and touches any part of his body, and then doesn’t wash his hands,” Curtis says, “any disease-causing microbes that he is carrying will be transmitted to the surfaces he touches afterwards.” These surfaces might include door knobs or other human hands.

Certainly the World Health Organization does not believe that hands are self-cleaning. It has invested heavily in hand hygiene with a global handwashing day and multiple campaigns aimed at educating people that handwashing is a matter of life and death.

Ackerley has no set guidelines on the number of times hands should be washed each day. Does she wash hers 20 times? Maybe 30? “Well, it might be much more than that,” she says. “Wash them when you need to.” This includes after going to the toilet, before preparing food, before eating even a bag of crisps, and when you return from school or work, to help keep your home germ-free. At buffets, Ackerley shakes hands with her right, and eats with her left.

“It is antisocial not to wash hands,” Curtis adds. “It puts other people at risk of sickness.” This is not an etiquette issue, she says. “This is a moral issue.”