SLS: Not good enough for aliens, so why think its good enough for you?
Figure 1. Old soap ad. (https://commons.wikimedia.org/wiki/File:Kirks_Soap_Yerkes_Mars.jpg)
The people on Mars are more intelligent than we ever could have imagined: they've chosen a soap free of sodium lauryl sulfate (SLS)! In order to understand why SLS might not be the best choice in soap, for aliens or for ourselves, its important to understand how soap works.
Of course, none of this means that you shouldn't use soap at all. There are many different alternatives to SLS like sorbitan laurate and cocamidopropyl betaine (1) that are gentler on skin and less likely to cause irritation! Its especially important to consider the cleanser you use if your skin is sensitive or you have eczema, as it is even more likely that SLS will strip and dry out your skin (3).
Remember: its important to be clean, but not at the expense of your skin!
References
The parts in soap that actually do the cleaning are called
surfactants (1). Although they don’t all look the same, the most common ones are
made up of two different parts (1): an end that likes to grab onto water because it
is polar like water, and an end that doesn’t like to be near water because it
is non-polar. The non-polar side would rather hang onto something that is more
like itself, like fat or oil. The polar side of the surfactant grabs onto the
water in the shower or from the sink, while the non-polar side grabs onto the
grease on your dirty skin. Since the two different parts of the surfactant are
attached to one another, they won’t split apart to keep hanging onto something
they like; instead, the surfactant will pull the grease with it, as it holds
onto the water, all the way down the drain (1).
For some, SLS does TOO good of a job clearing the oil from your skin. Because it is a very small
molecule and its non-polar end is charged and grabs on very tightly to oil, it can sneak into
the deeper layers of your skin and pull up the oil that your skin needs to
waterproof itself, which can cause dryness, flakes, and cracking skin (2,3). Bacteria
can creep into these cracks and cause infection! In fact, SLS is so good at its job that it is even used to clean industrial machinery (2)! Does that seem like thats the type of soap your skin needs?!
Of course, none of this means that you shouldn't use soap at all. There are many different alternatives to SLS like sorbitan laurate and cocamidopropyl betaine (1) that are gentler on skin and less likely to cause irritation! Its especially important to consider the cleanser you use if your skin is sensitive or you have eczema, as it is even more likely that SLS will strip and dry out your skin (3).
Remember: its important to be clean, but not at the expense of your skin!
References
(1)Walters, R.M., Fevola, M.J., LiBrizzi, J.L. &
Martin, K. (2008). Designing cleansers for the unique needs of baby skin. Cosmetics
& Toiletries, 123(12), p.
53-60. Retrieved from https://www.researchgate.net/profile/Russel_Walters/publication/257341452_Designing_cleansers_for_the_unique_needs_of_baby_skin/links/557cf59f08aeb61eae23658c.pdf
(2)Hazardous Safety Data
Bank (2015). Sodium lauryl sulfate. Retrieved from https://toxnet.nlm.nih.gov/cgi-bin/sis/search2/r?dbs+hsdb:@term+@rn+@rel+151-21-3
(3)DaSilva, S.C., Sahu, R.P., Konger, R.L., Perkins, S.M., Kaplan, M.H. & Travers,
J.B. (2012). Increased skin barrier disruption by sodium lauryl sulfate in mice
expressing a constitutively active STAT6 in T cells. Archives of
Dermatological Research, 304(1), 65-71. http://dx.doi.org/10.1007/s00403-011-1168-2
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