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The mystery and the science of SOAP!

Soap is a funny thing. It has the ability to clean things that are dirty, but when you try to describe how it works, most people find it's not really clear at all.


Soap is made by mixing an oil/fat with a strong aqueous alkali (a base, like lye (NaOH or KOH), dissolved in water), which causes a chemical reaction called saponification. This reaction releases a glycerin and creates potassium or sodium salt of the fatty acids from the triglycerides of the oil/fat (due to the alkaline pH). These fatty acid salts are the surfactant that is SOAP! These salt are either sodium based, when created using NaOH or potassium based from KOH. So, for example, if you used coconut oil and NaOH (lye) to make a bar of soap, you would end up with glycerin and sodium cocoate (the INCI name for the specific group of fatty acid salts created from the saponification of coconut oil by sodium hydroxide aka Lye or NaOH).


What is a Surfactant?


Surfactants are molecules that have a hydrophilic (water-loving) end and a hydrophobic (water-hating) end. This allows them to reduce the surface tension of water, which makes it easier for water to spread out and mix with other substances. Surfactants are used in a variety of products, including detergents, soaps, shampoos, and cosmetics. They are also used in industrial processes, such as oil recovery and wastewater treatment.


There are several different types of surfactants, each with its own unique properties.


Anionic: A negatively charged molecule that attracts positively charged particles and can be found in soaps, shampoos and detergents. (handcrafted soap falls into this category!)


Cationic: A positively charged molecule that attracts negatively charged particles and can be found in some personal care products like toothpaste or deodorant sticks.


Amphoteric: A mixture of both cationic and anionic properties which makes them good at cleaning both oily dirt from clothes as well as water-based stains from surfaces such as windows or floors (depending on the pH level).



How does Soap work?


The soap molecule, is made of three parts: a hydrophilic (water loving) head, a lipophilic (oil-loving aka hydrophobic or water-hating) tail and a middle section called the "internal water." Due to the attractions of these various parts, soap molecules form a structure called a 'Micelle' when mixed with water. A micelle is a sphere of soap molecules positioned with their hydrophobic heads facing outward and the lipophilic (hydrophobic) tails grouped into the center to "protect" the tails from the surrounding water. When you rub the soap and water on your hands, the soap molecules water-hating, lipophilic tails are attracted to the dirt particles as a place to hide from the surrounding water. As you rub you help break apart the dirt, oil etc into smaller particles allowing the soap molecules to more easily penetrate and surround these particles in a soap micelles. This process causes dirt particles to dissolve or disperse into water so they can be more easily washed away!


How does Soap remove/kill germs?


Bacteria and some viruses, (including SARS-CoV-2, that causes COVID-19) have a outer lipid membrane. This means soap can encapsulate them in a micelle the same way is does other dirt and oil. When the oil loving tail attaches to the germ it actually punctures and disrupts the lipid membrane of the cell. Some germs are killed when this happens while others are robust enough to survive, however like regular dirt and oil, they are rinsed away with the soap when we rinse with water. Lastly, soap is an alkalai is a substance with a high (basic) pH level (above 7). Bacteria and viruses don’t tend to find environments with high pH levels very hospitable because their cell membranes will break down if they hang out in them to long: so when you wash yourself with soap after touching something dirty like raw chicken or dog poop on the ground at the park where everyone goes crazy over their dogs but never pick up after them...the bacteria are being attacked by the pH, surrounded by the soap molecules and lastly, rinsed off down the drain if the first two fail to finish them off!


SO, How to we use soap effectively?


Wash with the right soap for the job! Use a soap designed for human skin and don’t turn the water too hot! A study published in the Journal of Food Protection revealed that cold water was just as effective as hot are removing germs and harmful bacteria.


Anyone who has washed oily or greasy hands knows hotter water removes oil more quickly by making the oil more fluid thus easier for the soap to penetrate and emulsify. However, during the average hand wash, it is unnecessary to use hot water. If you wash frequently with hot water you could be striping you skin of its natural oils and disrupting your skins protective moisture barrier. This barrier, consisting mainly of oil, helps trap water in our skin to help prevent dryness and irritation.


To wash properly, you don’t need a lot of soap (unless you're super dirty, greasy or oily for some reason!). In most cases as little as 0.5mL of soap is sufficient, and the amount of visible “lather” isn’t a factor because surfactants don’t need to foam to do their job. You just need to mix the soap with enough water to move the soap properly over the front and back of the hands up onto the wrists while you wash. Keeping the soap moist and rub it over all the areas of the hands for 10 second or more as the soap needs the time and agitation to help it detach the germs, oils and dirt from the skin and encase it in a micelle of soap so it can be easily rinsed away.


You should make sure you wash with soap


  • after using the bathroom

  • before eating

  • after handling raw meat or fish


Soap is good, but it's not the be-all and end-all of cleanliness. You can use too much soap. You can use the wrong kind of soap for the job at hand. And if you're not careful about how often you wash yourself with your favorite bar or liquid cleanser (and what kind), then there's a chance that all that scrubbing could actually cause damage to your skin in the long run by stripping away its natural oils--leading to dryness and irritation instead of what we all want: clean soft smoothness!



References

  1. Britannica, Surfactant, https://www.britannica.com/science/surfactant. Accessed April 2022.

  2. American Cleaning Institute, Ingredient Glossary, https://www.cleaninginstitute.org/understanding-products/ingredients/ingredient-glossary. Accessed April 2022.

  3. University of Illinois at Urbana-Champaign, Q & A: Soap!, https://van.physics.illinois.edu/qa/listing.php?id=465&t=soap!. Accessed April 2022.

  4. Britannica, Soap, https://www.britannica.com/science/soap. Accessed April 2022

  5. Dane A. Jensen, David R. Macinga, David J. Shumaker, Roberto Bellino, James W. Arbogast, Donald W. Schaffner; Quantifying the Effects of Water Temperature, Soap Volume, Lather Time, and Antimicrobial Soap as Variables in the Removal of Escherichia coli ATCC 11229 from Hands. J Food Prot 1 June 2017; 80 (6): 1022–1031. doi: https://doi.org/10.4315/0362-028X.JFP-16-370

  6. Michaels, B., Gangar, V., Schultz, A., Arenas, M., Curiale, M., Ayers, T. and Paulson, D. (2002), Water temperature as a factor in handwashing efficacy. Food Service Technology, 2: 139-149 . https://doi.org/10.1046/j.1471-5740.2002.00043.x


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