People are accustomed to put a large amount of detergent in the washing machine to do their laundry thinking that if there is not enough it won't clean the soiled clothing. But I have read that too much detergent will not clean as well as putting in a smaller amount. Why is that?

If the clothing is really soiled, you would think that a lot of detergent will attract more dirt and oil particles rather than a smaller amount of detergent.

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    $\begingroup$ I suspect that the required detergent increases fairly linearly with the amount of organic soiling present. It may be that large amounts of detergent molecules just adhere to themselves, possibly causing the detergent required for cleaning to preferentially associate with the excess detergent. However, I suspect this is all just some urban legend and that excess detergent is just wasteful but still cleans your clothes. Where did you read this claim? $\endgroup$ – airhuff Jan 9 '17 at 23:56
  • $\begingroup$ The amount of detergent you should use varies with the hardness of the water you feed your washing machine. $\endgroup$ – Jan Jan 10 '17 at 23:50

If your book stated that using a small amount of detergent would remove heavy soiling better than using a larger amount for a single wash, then I say it's bunk.

If your book stated that using too much detergent on a regular basis could result in a dirtier wardrobe, then there is a good explanation for that.

Let me use a more common but analogous process to explain: carpet cleaning. Though detergents generally work best in aqueous solution, residual, dried-up detergent still tends to bind to organics (or various types of undesirable "dirt") pretty well. So when one has a difficult to remove stain, they clean it repeatedly with highly concentrated detergent solutions that do not get thoroughly rinsed out of the carpet. Then, even if the stain is removed, that area quickly becomes soiled again due to the residual detergent sticking to more dirt than the rest of the detergent-free carpet.

Tying the carpet-cleaning analogy to laundering clothing is then pretty straight-forward. If one always uses more detergent than can be reasonably removed during the rinse cycle, then their clothing will tend to soil again more easily than if they had used an amount that could be largely removed during the rinse cycle. Thus, regularly laundering with too much detergent could result in a dirtier wardrobe than using a smaller amount of detergent.


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