Dr Chuck Gerba, professor of microbiology at the University of Arizona, studied how diseases are transferred through the environment. This involves swabbing household items and measuring how many bacteria - and what sort - develop.
In his studies, he particularly looked for faecal bacteria such as E.Coli and staphylococcus aureus, BBC News reported.
He found that on the average toilet seat there are 50 bacteria per square inch.
"It's one of the cleanest things you'll run across in terms of micro-organisms. It's our gold standard - there are not many things cleaner than a toilet seat when it comes to germs," he said.
People should be more worried about other household items, it seems.
"Usually there are about 200 times more faecal bacteria on the average cutting board than on a toilet seat," he said.
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In the kitchen it doesn't necessarily get there through actual contact with faeces. It comes via raw meat products or the viscera from inside of the animal, where a lot of the faecal bacteria originate.
The filthiest culprit in homes is the kitchen sponge or cloth. According to Gerba, there are about 10 million bacteria per square inch on a sponge, and a million on a dishcloth.
In other words, a kitchen sponge is 200,000 times dirtier than a toilet seat, and a dishcloth is 20,000 times dirtier.
This is the same the world over, the report said.
"Always the dirtiest thing by far is the kitchen sponge," said John Oxford, professor of virology at the University of London and chair of the Hygiene Council - an international body that compares hygiene standards across the world.