A US TV host has said on air that he has not washed his hands for 10 years because "germs are not a real thing" as he "can't see them".

Fox News host Pete Hegseth said the infectious micro-organisms did not exist because they could not be seen with the naked eye. "I inoculate myself," added the Harvard and Princeton graduate while speaking on Fox And Friends.

His remarks came on Sunday after show's co-hosts Ed Henry and Jedediah Bila mocked him for eating leftover pizza. "My 2019 resolution is to say things on air that I say off air," Hegseth said.

He later clarified that his comments were intended to be a joke and that he believed people were too fussy over cleanliness.

"We live in a society where people walk around with bottles of Purell (a hand sanitizer) in their pockets and they sanitise 19,000 times a day as if that's going to save their life.

"I take care of myself and all that, but I don't obsess over everything all the time," he told USA Today. 

His comments were met with both support and concern on social media. One Twitter user wrote: "I wonder if @PeteHegseth would be cool with restaurant workers preparing his food after deliberately not washing their hands?"

Another said: "I'm with you on hand washing. I'm almost 70 and haven't had a cold or flu in years. Our bodies need some germs to learn how to fight them. Too many germofobes out there."

Talking about the public reaction to his remaks, Hegseth said it was ridiculous how people took things so "literally and seriously" so that their "heads explode".

Daily hand washing, according to the US-based Centres for Disease Control and Prevention, "is one of the best ways to remove germs, avoid getting sick and prevent the spread of germs to others".

A study by the US National Centre for Biotechnology Information, said that one gram of human faeces - about the weight of a paper clip - can contain one trillion germs.