Is hand-washing after urination and defecation merely a product of social norms, or is there a health-related reason that we wash our hands after going to the bathroom? Or is there some other reason altogether?
Without washing your hands after going to the toilet, you are running the risk of E. coli enteritis. E-Coli can lead to severe illness or even death. Keep in mind, every time you flush the toilet that a plume of water droplets can spread by up to a couple of metres, coating tooth brushes and such in contaminant. This is also backed up here.
In response to OddThinking: If you were to only touch yourself I would reason that the risk remains. As noted above, everything within a few metres of the loo is likely to be swimming in bacteria, especially if the lid was not closed when it was last flushed. So just entering the bathroom is problematic.
Furthermore, people fart about a litre of gas a day. Since farts contain bacteria, you can pretty much assume your clothes and body are also contaminated. This was posted on Dr Karl's site. The Naked Scientist tested the effect of clothing on bacterial content of farts and found the clothes (jeans + undies) seem to absorb the bacteria.
Taking this further: can you make yourself sick with your own facel material? Given that 20% of food poisoning occurs at home, I would think so.
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