Laundry soap vs detergent: hygiene, and the environment.
September 22, 2017 4:19 PM   Subscribe

I read a site that claims that soap doesn't get laundry properly clean, that detergents found in most commercial laundry powders are more effective. Is that true? And are laundry detergents still ecologically damaging?

The site I read was this:

My understanding from high-school chemistry was that soap works fine in soft water but leaves scum in hard water. So if you add washing soda to soap powder (for homemade laundry powder), that should make the water soft, and then I don't see why the soap should leave mineral/scum deposits?

(this is all relevant because the laundry powder (Bio-D) I'm using is based on a vegetable soap and washing soda: I did specifically ask the manufacturer - it actually is soap, not detergent.)
posted by tangerine_poppies to Science & Nature (2 answers total) 3 users marked this as a favorite
Well, soap is made from oils/fats, so while it's better for your skin, I could see where it might leave a residue on clothes. Adding household vinegar to your final rinse would probably get rid of any residue. A quick scan of relevant soap/detergent/laundry articles on Wikipedia seems to say that yes, detergent is still bad for the environment.

Incidentally, in the US, the bars of "soap" you buy at the grocery store for washing your body are actually almost always detergent and are very drying on your skin. (Legally, in the US detergents are allowed to be called soap.) Switching to handmade soap, especially glycerin soaps, made a big difference in my skin.
posted by MexicanYenta at 3:48 AM on September 23 [1 favorite]

soap doesn't get laundry properly clean, that detergents found in most commercial laundry powders are more effective. Is that true?
Basically: yes. Soaps do not clean fabrics well. You should use a laundry detergent.

Detergents are much more effective, because they have surfactants which are specially made to maintain their activity in the use environment (fabric/water/heat/dirt), and therefore are available to be used for their intended purpose (removing dirt/oil/gunk from fabrics, and subsequently being washed away with water). Detergents that are specifically laundry detergents also have other ingredients that help remove other types of stains (enzyme additives), preserve textiles, work in modern washers (HE especially), and have shelf-stable formulations.

are laundry detergents still ecologically damaging?
The Sweethome has a good overview of ingredients of most concern from detergents, but the chemical usually cited as the ecological problem was phosphates, which led to massive algal blooms & pollution - but these haven't been used since ~1990s in US (not sure about other countries).

Some more info on terminology/science:
The distinction of "soap" vs "detergent" isn't a scientific one (Merriam-Webster detergent: a cleaning agent, such as (1) soap). "Soap" most commonly means sodium stearate, a molecule that's a surfactant - which is also what a detergent is defined as being (a surfactant). Other "soaps" (i.e. molecules derived from saponification of fatty acids) are also surfactants aka detergents.

Sodium stearate is, as I mentioned, not a great choice for cleaning (laundry, dishes, etc) because it reacts with minerals in water and precipitates (that's soap scum!), which means that amount of soap is no longer available to act as a cleaning agent. Leigh Boerner (a chemist and author of the Sweethome piece I linked above) has written more about the chemistry of soap / detergents in the context of consumer products, so this or this post might also be helpful.
posted by chemicalsyntheticist at 2:12 PM on October 9

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