Women frequently complain about men failing to put the loo seat down after a pee. (What’s the problem? Do women have difficulty lowering the seat themselves?) But in my clearly limited experience, those men who do elect to replace the seat also tend to put the lid down too — which is something that women almost never seem to do when they have finished their lavatorial business.

Does it matter if you don’t drop the lid? Yes, it does. It really does.

The lid is not there just for cosmetic reasons. It has a valuable hygiene-related purpose that means you should always lower it before you flush the loo.

Research has shown that the force generated by a post-poo flush creates an invisible mist that contains significant quantities of aerosolised faecal bacteria. This bug-filled cloud, known as “toilet plume”, rises from the toilet pan and spreads right across even the largest bathroom, so that it contaminates towels, taps and — ugh! — toothbrushes. Lowering the lid before you flush will greatly reduce the risk of such contagion.

Researchers at an American university tested toothbrushes kept in communal bathrooms and found that more than half were contaminated with faecal coliform bacteria. And in shared bathrooms, these bacteria are likely to have come from someone else’s bum. Yuk! So you should always lower the lid before flushing and you should press other loo users to do likewise.

Don’t poo-poo this suggestion.

Furthermore, the research findings indicate that you should always wash your toothbrush well before squeezing your nurdle of toothpaste onto it. Brushing your teeth with your own coliform bacteria may not pose a problem, but ingesting bacteria derived from other people’s guts could put you at risk of a nasty infection.

The benefits of lowering the loo lid obviously also apply to lavatories accessible to the public. Unfortunately, the WCs in many public loos do not feature lids, so you cannot reduce the spread of aerosolised bacteria even if you want to. OK, so you are not likely to brush your teeth in a public convenience, but you are still at risk of unwittingly ingesting or inhaling faecal microbes from other people’s toilet plume.

(Incidentally, lavatory lids are not necessarily designed to be sat upon. If you choose to park yourself on the loo lid — for instance, while supervising your children’s bath time — you risk cracking even the most expensive lid.)