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Some people do their dishes and leave the suds on, letting it air-dry, or using a towel. Some rinse it off.

I cannot understand the British habit of washing and rinsing dishes in the same dirty water, and drying them without washing off the soap suds. Is this similar to having a bath and not rinsing off the soap? Am I missing something here?

Letter – The Guardian, UK

Ecological water-saving, dirty towels, or nasty soap taste-arguments aside: I wonder if it is unhealthy to leave the suds on, and as a result, ingest minor traces of soap when drinking/eating.

With most washing-up liquids being relatively newer formulations from petrochemicals, to which long-term exposure is still unknown, residuals cannot be beneficial if ingested. The health effects are probably on the order of second-hand smoking; chronic exposure adds up, incidental exposure is probably innocuous.

Answer to the above letter – The Guardian, UK

What does scientific research say?

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Nevertheless the answers should not focus on the towel too much as this is possibly the main source of recontamination after washing. (would be nice of course to know if so and how much of an effect this has) – Informaficker Aug 27 '12 at 10:23
4  
"...relatively newer formulations from petrochemicals, to which long-term exposure is still unknown, residuals cannot be beneficial if ingested..." is illogical: unknown is clearly inconsistent with cannot – Henry Aug 27 '12 at 11:29
this is very anecdotal: A physicist once explained to me that the soap would create a thin layer which drains any dirt and itself due to gravity. – Anno2001 Nov 3 '12 at 19:48

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