At first, it was SLS that got demonized, then the rest of sulfates and now pretty much any surfactant that is being used in the shampoo has at least one article somewhere on the internet calling to avoid it at all cost. What is really going on? – one might wonder.
Where it all stems from is that Sodium Lauryl Sulfate (SLS) has a pretty small molecule, and that is one of the reasons why it is considered a classic irritant. When dermatologists study soothing and calming properties of various ingredients, they need an irritated skin to start with as a baseline, and SLS is typically used for that purpose in a skin patch applied to the forearm between 10 minutes to 24 hours. What happens is that since this detergent ingredient (surfactant) is great at stripping oil from the hair or skin, it also breaks the intercellular lipids when left onto the skin for a prolonged time. And at a high concentration it can even break cells and strip protein from them. Messing up with the skin lipids impairs the skin’s ability to retain water.
However, it is important to note, that unlike patch testing, we apply shampoo for a few seconds, and then thoroughly wash our hair and skin. Therefore most people do not notice any effect of powerful detergents other than cle
Now, how about other types of detergents?
Here is a good comparison table from the study that analyzed various popular shampoo ingredients and their irritancy:
|Sodium Lauryl Sulfate||192.90|
|Ammonium Lauryl Sulfate||176.82|
|Sodium Laureth Sulfate||41.02|
|Sodium Myreth Sulfate||17.76|
|Disodium Cocoyl Glutamate||4.88|
|Disodium Laureth Sulfosuccinate||4.67|
|Laurdimonium Hydroxypropyl Hydrolyzed Wheat Protein||2.99|
|Sodium Cocoyl Hydrolyzed Wheat Protein||2.62|
|Sodium Cocoyl Hydrolyzed Wheat Protein Glutamate||2.33|
Few conclusions can be made by looking at the results of this and other studies that also looked at other types of ingredients:
- Water is obviously an irritant too, as it is capable of stripping skin’s lipids.
- Not all sulfates are created equal, and since Sodium Laureth Sulfate has a larger molecule it has a lower irritation potential than the rest of the sulfates that made the top of the list
- Acetates tend to be in the middle on the irritancy scale, isethionates are lower than that and glucosides are least irritating.
By looking at this list, one might think: “If it is obvious which ingredients are irritating, why not avoid them altogether?” Well, pretty much for the same reason why washing our hair with just water is not sufficient. The more irritating the ingredient is, the more efficient it often is at cleaning the hair and therefore can be used at a lower concentration to achieve the same effect than a milder ingredient. Coincidentally, lower concentration also reduces the irritation potential. If someone wants to make a shampoo that is less irritating, stripping less protein and protects the hair color, the simplest way is to put less detergent in the formula. Unfortunately, it means that some customers will have to wash their hair twice.
Different shampoo ingredients also have different properties. For instance, the category of glucosides creates an unruly and impossible-to-comb hair. No customer would want to wash their hair with the shampoo based solely on glucosides. However, kids hair is often based on a simple cocamidopropyl betaine, as it doesn’t require thorough washing and simply offers a decent foam. If you are not sure whether your skin is sensitive to sulfates, this might be a safe test to try.
Usually scientists combine several different surfactants in their shampoo to ensure that the combination provides the exact efficiency they are aiming for a specific hair type. Moreover, combining multiple surfactants often has a synergistic effect: together even at a higher concentration the reduce the irritancy potential compared to high-irritant one used at a lower concentration. The other benefit of combining multiple different surfactants is that it allows to combine the molecules of different sizes and create the bubbles of various sizes too, which makes foam more stable.
At the end of the day the factors that really matter when choosing a shampoo are:
- Is your hair very oily? If that’s the case, then milder shampoo might not be a savior. If you end up washing your hair twice, you end up stripping as much protein but use essentially the double amount of product. You might though opt for shampoos where SLS is not the first ingredient on the list.
- Is your hair dry? You can experiment with milder shampoos that would offer just the right balance of cleaning yet not stripping too much of the oil and protein. However, if you use hair conditioners and styling products your mild shampoo might not be as efficient at removing the build-up. Considering rotation might be a good approach.
- Does your hair have “special needs”? Maybe it’s curly, damaged or colored. All these factors can add up to the overall hair routine and your choice of shampoo. Some people with curly and dry hair swear by “co-washing” and are able to avoid shampoo altogether.