Kicking off Wednesday posts in 2016, like to explore this group of ingredients which is present in all cleansers but also have the potential to irritate skin.
Surfactants are ingredients that are active on surfaces, mainly to lower the surface tension on the skin and remove dirt, sebum, oil from cosmetic products, microorganisms and exfoliated skin cells in an emulsified form to be washed off. The different type of surfactants affect their cleansing, foaming/ lathering, emulsifying, solubilizing abilities as well as its potential to irritate.
Why not just Water?
Before we go on, the simple question to ask is why not just use water to clean our skin. This is because water alone is not effective in removing dirt which can be removed only by oil. Hydrophilic dirt can be removed only by water, and fat-soluble lipophilic dirt only by oils.
Groups of Surfactants
Surfactants are divided into hydrophilic (water loving), hydrophobic (water repelling) and lipophilic (oil loving). Surfactants consist of a fat-soluble (lipophilic) part and a water-soluble (hydrophilic) part. The lipophilic part sticks to oil and dirt, and the hydrophilic part allows it to be washed away.
Surfactants perform different functions, namely:
- Cleansing
- Emulsification – arrange itself at interface between two immiscible liquids to create an emulsion
- Solubilization – blending oily solution into clear liquid
- Conditioning
- Wetting – increase contact between the product and dirt
Apart from functions, manufacturers also consider mildness, biodegradability, toxicity, moisturization, skin appearance and feel, smell (fragrance) and lubrication when formulating their products.
There are four major groups of surfactants, classified by their polar hydrophilic (water loving) head group:
- Anionic
- Cationic
- Amphoteric
- Non-Ionic
Anionic Surfactants – Negative charge
Give effective cleansing and foam, good wetting properties, excellent lather characteristics, but moderate disinfectant properties and also likely to irritate skin.
E.g. Carboxylic acids – Stearic acid for stick products like deodorants and antiperspirants; Sodium stearate for soap
Sulfates – give effective cleansing, foaming and cheap; common irritant, e.g. Sodium lauryl sulfate (SLS), an alkyl sulfate used in detergents; Sodium laureth sulfate (SLES), an alkyl ether sulfate used in shampoo
Sulfonic acid surfactants – more expensive than sulfates but less irritating, e.g. dioctyl sodium sulfosuccinate, alkyl benzene sulfonate
Taurates (derived from taurine), Isethionates, Olefin sulfonates, and Sulfosuccinates.
Phosphate esters – Alkyl aryl ether phosphates; alkyl ether phosphates
Cationic Surfactants – Positive charge
Effective for conditioning cosmetics, positive charge makes the surfactants electrostatically attracted to the negative (damaged) sites on hair and skin protein which makes them resist rinse-off. Difficult to ‘mix’ with Anionic Surfactants. Also irritate. May be used as antimicrobial preservatives due to ability to kill bacteria.
E.g. Amines
Alkylimidazolines
Alkoxylated Amines
Quaternized Ammonium Compounds (or Quats). e.g. Cetrimonium chloride and Stearalkonium Chloride
Amphoteric surfactants – both positive and negative charge (depending on environment)
Help improve foaming, conditioning and reduce irritation. Moderate antimicrobial activity. Used in mild cleansing products, but not effective cleansers and emulsifiers. Both Alkaline and Acid, help to adjust the pH of the water used in solution.
E.g. Sodium Lauriminodipropionate and Disodium Lauroamphodiacetate.
Cocamidopropyl betaine, cocoamphoacetate and cocoamphodiacetate
Non ionic Surfactants – No charge
Used in heavy thick creams, such as hand or body creams, as emulsifiers, conditioning ingredients, and solubilizing agents.
Relatively low potential toxicity and they are considered the most gentle surfactants, but they are also the most expensive
Able to solubilize fatty acids and cholesterol in skin, thus may remove skin lipids
E.g. Cocamide DEA (coconut diethanolamide), widely used in personal care products for its thickener property and foam booster
Fatty acid esters of fatty alcohols, sorbitan esters, sucrose and cholesterol derivatives used like emulsifiers
In the following Wednesdays of this month, we will explore the impact of surfactants on skin, baby and eczema skin and some of the research in this area. I’m learning much about this as I read as well and it’s not all so easy to understand! Any expert reading this who would like to help out are welcomed, do leave a comment if you have expertise in this area or there’s something to correct in my post (no offense will be taken!).
References
- Chemist’s Corner – Learn to Formulate Cosmetic Products
- Beauty Review – Surfactants, skin cleansing protagonists