Introduction
SCI, scientifically known under INCI (International Nomenclature Cosmetic Ingredient) as Sodium cocoyl isethionate, is an ingredient in many cosmetics due to its properties as a surfactant. Surfactants are added to soaps for their ability to remove particles from the hair and skin. It is also known as baby foam because it is a very gentle cleanser and leaves the skin smooth. This makes it one of the most popular surfactants: it leaves behind smooth, clean, and soft skin without the excessive drying of other cleansers and detergents.
What are its physical and chemical properties?
At the molecular level, it has two parts. The first of these is a negatively charged or anionic ‘head’ made up of a sulfonate. Sulfonates are hydrophilic, which means they are attracted to water molecules. The second part of the SCI molecule is the fatty acid ‘tail.’ This half is hydrophobic, meaning it is repelled by water molecules. While ‘head’ is pulled towards the water, the ‘tail’ is pushed away from it and towards the oil. This is what makes it a surfactant: it can bridge the gap between water and oil.
This makes it a good emulsifier as it can decrease the surface tension between the oil and water, which in turn causes the oil to rinse off as if it was soluble in water. SCI is only slightly soluble in water (about 1% in 25º C water) because it is a fatty acid. Most carbon based (organic) molecules are insoluble in water. However, it is soluble in other surfactants or organic solvents. In water, it has a pH of 5.5 – around the acidity of coffee or milk. Depending on the concentration of SCI in the final product, it can range from 5.0 to 7.0. Human skin has a natural pH of 4.5 to 6.2, making it slightly acidic. Skincare products usually have a pH of 5.0 to 7.5 in order to maintain this balance. Fortunately, SCI is smack dab in the middle of that range. Some cleansers have pHs over 9, which is very bad for the skin.
Is it a sulfate?
Many shampoos and conditioners are advertised as ‘sulfate free.’ Sulfates are notorious for the way they dry out and irritate skin. While SCI contains sulfur, it does not have any sulfates. Instead, the sulfur in SCI takes the form of a sulfonate. Sulfates have four oxygens, one of which is bonded to the fatty acid. Sulfonates, on the other hand, have three oxygens and are linked directly to the fatty acid tail.
What does it look like?
At room temperature, it is a white, waxy, solid that is soaplike in odor. It can be bought in the form of chips, flakes, or a fine powder. If added to a liquid product, it must be melted down first as it is only somewhat soluble in water. It can be used in transparent gels and soaps without making them opaque. SCI is also tolerant of hard water as well as soft water, which makes it an excellent choice. It does not form soap scum. Another bonus is that it is an organic compound and is therefore biodegradable.
How is it made?
It is made by reacting the fatty acids found in coconut oil with sodium isethionate, a weak organic acid. Next, it is heated and distilled to remove excess water and any remaining fatty acids. Finally, it is ground or shaped into its final form. It is sold in many forms. The most common are small flakes, pill-sized lumps, ‘noodle’ strands, and powder. SCI is also a biorenewable resource because it comes from plants.
What makes this surfactant different from others is that it is less of a skin irritant than other compounds. Sulfates such as sodium lauryl sulfate are more damaging to the skin as they dry out the skin. This is where SCI gets the name ‘Baby Foam.’ It is known for being so gentle that it could be used on the delicate skin of a newborn child.
How is it used?
SCI is used in soaps, shampoos, gels, foams, and many more products due to its gentle cleansing and moisturizing properties. In some products, it can be added in the powdered form without any extra steps. If it is to be added to a liquid or from the flake form, however, it must be melted first. To dissolve it, add it to the rest of the surfactants over steady heat and stir.
In soaps and shampoos, it foams up to create a rich lather. This enhances the cleansing action of the product without drying out the skin. It makes hair and skin softer to the touch without causing dryness or irritation. SCI is also an emollient – it binds water to the hair to make it glossier. Finally, it can preserve skincare products to give them a longer shelf life.
How strong is it?
Rinse-off products such as shampoo and conditioner usually have a concentration of 50% SCI. Leave-on products such as hair serums have a low concentration around 15-17%. Products with concentrations above those levels can be harmful if used for a long period of time. SCI has an active surfactant level of 84%. As a result, almost all of it is at work and very little remains as filler.
What can I substitute it for?
One common question is what to do if for whatever reason, you can’t obtain SCI. Keep in mind that SCI is the most gentle of the solid anionic surfactants. A replacement may be harsher on the skin than SCI. The most common replacement is SLS-a or Sodium lauryl sulfoacetate. Other options include sodium lauryl sulfate (SLS), sodium coco sulfate (SCS), and sodium C14-16 olefin sulfonate (Bio-Terge AS90).
Is it safe to use?
Yes. SCI is very gentle on the skin when used properly. It is non-toxic, non-irritating, and a nonallergen. However, one should remember to be careful when working with fine powders as they can be dangerous if inhaled. Always wear an N95 or other particulate-filtering mask when using the powdered form. Take care to ensure it does not come into contact with the eyes, as it can cause irritation. If it does come in contact with the eyes, rinse them with water for fifteen minutes. In the event that irritation persists, seek medical attention. Store any unused SCI in a cool, dry, and dark area.
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