This month, we’re looking at surfactants – the chemical agents in cleansing products. It is important because while surfactants play an important cleansing function, they also potentially cause skin irritation. Last two weeks, we have understood:
- Different groups of surfactants and their functions – Anionic, Cationic, Amphoteric and Non-ionic surfactants
- What to Look out for when Cleansing Baby Skin – Discussion on the use of liquid cleanser being preferable to water, and what to look out for in the choice of liquid cleanser
Today, we’re looking more in-depth into how surfactants interact with skin and the potential harm to our skin.
Alkalization – The traditional soap is alkaline in nature (pH of 9 and above) and the alkalinity will increase the skin pH (which is of pH 4.6 to 5.6). Modifying the skin pH to more alkaline than it is supposed to be has the impact of (i) reducing skin lipids, including ceramides (ii) allows for growth of harmful bacteria like staph bacteria that thrives in a more alkaline environment and (iii) increases transepidermal water loss (TEWL). Alkaline soap is able to dissolve both fat and water-soluble components of skin. Synthetic cleansers are of varying pH and able to modify the pH of the cleansing product.
Damage to Skin Lipids – Surfactants are able to clean dirt and sebum that are oil-soluble. However, this property also means that surfactants may inadvertently solubilize the skin natural lipid membranes (ceramides). Stronger anionic surfactants like Sodium Lauryl Sulphate (SLS) enhances penetration into the skin and able to affect the deeper skin cells (skin lipids).
Damage to Skin Cells – During washing, the surfactants interact with the skin cells and collagen fibers and cause temporarily swelling and hyper-hydration. Once the water evaporates, there is destruction of the skin protein structures (known as denaturation) and leads to skin dryness, roughness, tightness and scaling. This is an adverse effect of anionic surfactant.
Toxic to Skin Cells – Known as cytotoxicity, surfactants can permeate skin cells and cause irreparable alteration. Certain surfactants such as benzalkonium chloride and cocamidopropyl betaine (CAPB) are known to be more cytotoxic than SLS. CAPB is an amphoteric surfactant, a group of surfactant less irritating than anionic surfactant (SLS belongs to anionic group) but nonetheless can be cytotoxic. CAPB is also associated with allergic contact dermatitis.
Irritation to Skin – This is related to the duration of exposure, frequency, concentration and individual skin type. SLS is a known irritant that can cause skin inflammation (irritant contact dermatitis) and when combined with triclosan (an antibacterial and antifungal agent in products), can stay on the skin for hours/days. Amphoteric and nonionic surfactants are considered to be less irritating to skin. (Note: Skin irritation and cytotoxity are different concepts.)
What to Note when Choosing Cleansing Products
Based on the above surfactant interaction with skin, it follows that we ought to choose:
- Products close to the skin pH (even water is not, either neutral pH 7 or sometimes more alkali)
- It follows then to avoid soaps, which by nature are alkaline
- Avoid SLS, as it can penetrate, damage and irritant skin
- Avoid CAPB as it is cytotoxic
- Choose products with larger micelles as they do not penetrate the skin cells as much (product packaging may not indicate this information so it’s quite hard to know; look out for Polyethylene oxide (PEO)/ PEO Sorbitan Laurate which forms larger micelles in the surfactant or for the term Hydrophobically Modified Polymers (HMPs))
- Choose cleansing products that are moisturizing and moisturize right after washing
- Reduce washing for prolonged time and frequent washing
- Avoid alcohols, gels and alphahydroxy acids that can cause stinging
- Avoid perfume, benzoyl peroxide, preservatives, parabens, propylene glycol, lanolin, methylisothiazolinone and other top irritants in this post
- Avoid ingredients ending with sulfates
It is not easy to find a cleanser without any of the above-mentioned ingredient. For those with sensitive skin, it may be better to not wash as often and take care to choose a hypoallergenic product. Try to read the ingredient label of your product and be sure that the first few ingredients are at least not those in this post.
- The Infant Skin Barrier: Can We Preserve, Protect, and Enhance the Barrier? Dermatology Research and Practice Volume 2012
- Surfactants, skin cleansing protagonists Beauty Review
- Status of surfactants as penetration enhancers in transdermal drug delivery J Pharm Bioallied Sci. 2012 Jan-Mar; 4(1): 2–9
- The impact on skin depends on the surfactant concentration, the type of exposure, the duration of contact, and the individual response. Dermatology Research and Practice, Volume 2012