What You Should Know About Soap for your Oily Skin

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If you were ever plagued by an oily skin condition, you probably have had the urge to get relief by giving your skin a good scrubbing with soap to make it squeaky clean. Unfortunately you probably found out that this only helped for a very short period of time and the oil came back with a vengeance. So, what should you do? Should you use soap, and if yes, what kind of soap?
Because there is so much misinformation on this topic, we wrote this post. As regulars at Sana Fela have come to expect, this article is based on what science has to say about the topic.
Let’s first find out a bit more about what soap actually is.
What is Soap Anyway?
Soap is made in a process called saponification. Animal or plant fats are treated with hydroxide (lye) which hydrolyzes the fatty acids. The main animal fat comes from rendered body fat obtained from the meat industry. In the United States the main plant fat for soap comes from coconut and palm oil [1]. You can find a summary of the chemistry of saponification and general structural formula on about.com.
The properties of the soap being manufactured depend in part on the chain length of the fatty acids that are used. The shorter the chain length (less than 12 amino acids), the more irritating the soap will be [1]. The longer the chain length, the harder the soap is and the smaller the bubbles in the soap lather will be. Shorter chains create softer soap and lather with larger bubbles. Small bubbles last longer than large bubbles, so the longer fatty acid chains produce dense and longer lasting lather.
Animal fats mostly yield long chain fatty acids whereas the short chain fatty acids are mostly derived from plant fats. By mixing animal and plant fats the hardness and type of lather of the soap bar can be set to whatever is intended. The hardness of the soap is also determined by the type of lye that is used. Sodium hydroxide will produce a harder soap as compared to potasium hydroxide. The solvents that are used to dissolve the fragrances that are used in soaps tend to make the soap softer.
Soap Additives
A whole host of substances can be added to the soap base to change its properties, give it a longer shelf life, or make it smell good. Some of the more important ones to keep in mind when looking for soap are mentioned here.
Unsaturated plant fatty acids easily oxidize in air, so it is necessary to add preservatives such as EDTA (EthyleneDiamineTetraAcetic Acid), citric acid or butylated hydroxy toluene.
Glycerin is a byproduct of saponification and is thus found naturally in soap. Glycerin absorbs water and is commonly used as a moisturizer. The amount of glycerin in soap determines how easy it is to rinse the soap away. Examples of other skin conditioners that are often added to soaps are aloe, lanolin and vitamin E.
Other additives that can be used in soaps are things like exfoliants (e.g. pumice), anti-acne additives, as well as fillers such as resins and talcum. The color and transparency of soap can be changed by the addition of pigments, dyes, and metal oxides, most often zinc oxide and titanium oxide.
The topic of soap ingredients and additives is extensive. Stay tuned for future posts and an ebook that will go into the details and pros and cons of the various constituents of soaps and creams with an eye on oily skin and acne. You can also
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How Does Soap Clean?
Soap cleans by changing the surface tension of water and by solubilizing and suspending dirt which then can be rinsed away. Soap molecules have an apolar hydrophobic and a polar hydrophilic end. The hydrophobic (fat loving) parts of the molecules bind to oily or greasy dirt, causing the hydrophilic (water loving) parts of the soap molecules to orient themselves toward water. The soap thus acts as a bridge between the water and the dirt, allowing the dirt to be held in suspension and to be washed away.
Regular Soap Can Be Detrimental to Oily Skin
Your skin protects itself from the environment by the acidic mantle [2]. The acidic mantle consists of a mixture of oil from the sebaceous glands and secretions from your sweat glands. Among other things, it contains fatty acids that have antibacterial properties. As a result, the pH of your skin normally is acidic. While the skin of a newborn baby is just about neutral (pH 7), the pH of the skin becomes more acid as you get older. The skin of adults is usually slightly to moderately acidic (pH 4.5 to 6.5).
When your skin is too oily, your sebaceous glands are overdoing it and secreting too much oil. However, you can’t just remove all the oil in any old way, since any kind of irritation to the sebaceous glands can cause them to secrete even more oil. To prevent irritation as much as possible, you need to use a soap that does not change the pH of the skin, or at least does not flip it from the natural acidic into the alkaline range.
After you have read above how hydroxides are used to make soap, it is not surprising that a standard bar of soap is quite alkaline. If you use regular soap, the pH of the washed skin will turn alkaline. This irritates the skin which then responds by producing more oil as it tries to protect itself.
Soap Formulations for Oily Skin
As explained above, the pH changes of your skin that are caused by regular alkaline soap, while doing a great job cleaning, cause irritation which stimulates the skin to keep on over-producing oil. When you have oily skin, you should look for soaps that are specifically formulated to have a neutral or acidic pH. The pH of traditional bar soap is around pH 10. This pH can be lowered and neutralized by adding an excess of free fatty acids that are not saponified. This is referred to as “superfatting” of soap [1].
The Best Soap for Oily Skin is Not Really Soap At All
The best soaps for oily skin are not soaps at all. This refers to a group of products called the Syndets. Syndet is an acronym for Synthetic Detergent [3]. These are really detergents that can be in the form of a bar of soap, but also may be thick liquids.
Because no hydroxides are involved in the production of Syndets, they can be made at a wide variety of pH. Syndets contain synthetic surfactants that cause less irritation and have better “skin feel” and conditioning and moisturizing properties as compared to traditional soaps. Such synthetic soaps generally are much milder for the skin and have superior lather properties. They also typically have more conditioners and moisturizers. A well known example is Dove.
There are also mixtures of traditional soap and Syndets. Such mixtures are usually referred to as Combars. Well known examples are Zest and Ever 2000.
Recommendations for Oily Skin
If you have oily skin, it is important to wash your face with a soap that has a mildly acidic pH and is non-irritating to the skin. As explained above, some of the best choices are superfatted acidic soaps as well as acidic Syndet based formulations. Also, keep in mind that longer amino acid chains tend to be less irritating. As always, having a little knowledge and reading product labels goes a long way to make the right choices for your skin care.

References
[1] Handbook of Cosmetic Science and Technology
[2] Schmid MH and Korting HC (1995) The concept of the acid mantle of the skin: its relevance for the choice of skin cleaners. Dermatology 191: 276-280
[3] Kirsners RS and Froelich CW (1998) Soaps and detergents: understanding their composition and effect. Ostomy Wound Manage 44: 62S-69S