quesarah | science lesson: on the soapbox

On the soapbox

Okay, brief discussion of SDS (so called by researchers because it's an abbreviation of its proper IUPAC name, Sodium Dodecyl Sulfate rather than the antiquated Sodium Lauryl Sulfate).

First, remember that saying about oil and water not mixing? Well, it's very true and related to very specific chemical properties. That's why it's so difficult to get greasy stains out of your wash; the oils don't want to come out into the water and would rather hang on to the fibers of your clothes. This is where detergents come in, 'cause they're little split personality chemicals that have a greasy part on one end that mixes well with oils, and a salty part on the other end that mixes well with water. If you bring it into the picture, the greasy end will bundle up any oil that's on your clothing and let it be dissolved in the wash water.

This is handy for a lot of reasons, namely the fact that our bodies produce a lot of greasy fatty acids (perspiration, hair oil) that most of us would like to wash off in the shower, the laundry, and so on. And just so you know, the difference between the greasy oily stuff made by our bodies and something like engine oil is minimal: engine oils are made from the breakdown of plant substances while the stuff on our bodies is (obviously) from animal sources. Chemically speaking, they're more alike than not. This is why detergents like SDS can be found in a number of cleaning products; it does a wide spectrum of degreasing jobs.

The other nifty thing about detergents is the effect they have on cell membranes, the little capsule keeping a cell's contents together. Membranes are made of fatty stuff too, so a detergent will dissolve the membranes just like it would any other grease or oil. The end result: the cell pops open and dies. This is the reason "antibacterial soap" is completely unnecessary: all soap is by its chemical nature antibacterial! When you wash your hands well with soap and water, you're popping open the cell membranes of any bacteria that are on your skin. Therefore, soap and water = an "anti" (against) bacterial agent.

Now, the caveat: detergents can pull the greasy stuff out of cell membranes in your skin, too. This is why some soaps dry your skin out: these are the harsh soaps that do little bits of damage to it every time you wash. This is something to be aware of if you have sensitive or dry skin, or if you're using a product on a baby.

Regarding the variations of SDS you see, such as "sodium laureth sulfate" and "ammonium laureth sulfate:" these are all variations of the chemical that make it less strong a detergent. If you make the greasy part slightly less greasy (lauryl --> laureth) or the salty part less salty (sodium --> ammonium) it will make the soap slightly less stringent and hopefully more gentle on skin, hair, etc. It might do its degreasing job slightly less well but for cosmetic products it's a reasonable compromise.

/ end science lesson