Sulfates get a lot of press, but for all the wrong reasons. And to really understand them, we need to start at the beginning. First, sulfates are part of a surfactant system in all sorts of beauty products designed to clean, so not just shampoos, also check your body wash, face wash, and hand soaps. Sulfates are just a generic term for “sulfate-containing surfactants.” Sulfates have been used since the 1940’s in beauty products like shampoos and have been studied for their safety extensively since then. Most people don’t know, but sulfates are derived from palm kernel oil and coconut oil. Are they natural? Not exactly, while they have natural sources, they are several steps away from their natural source. So check your label, anyone claiming natural sulfates in their shampoo is stretching the truth.
So what are they, then? As with all surfactants in shampoos, sulfates have one part of them that likes water, and one part of them that likes oil – and this is how they are able effectively clean. However tradeoffs do exist; there are sulfates that are great at cleaning and lather generation, but they can be harsher on skin. Vice versa, sulfates that are mild are generally not great at cleaning. Therefore a balance is required to get a shampoo that cleans well, while still being mild. This balance is a function of the whole shampoo formula, where ratios of good cleaning sulfates (lauryl) and very mild sulfates (laureth) are combined. Its worth mentioning in the total formula as well, that silicones and polymers in your shampoo also contribute to the mildness and protection against breakage of your hair.
So what is in a sulfate-free shampoo? Is it really more gentle? First, sulfate-free shampoo does not equal surfactant free! If that were the case, your shampoo would not clean or lather. On a structural standpoint, sulfate-free molecules also have one part of them that likes water, and one that likes oil. After that, it becomes a tricky name game. For example, Isethionate, a common “sulfate alternative” is a sulfonate, mimicking the structure of sulfate with the exception of one molecule. Ingredient statements can actually be misleading in this case!! Because sulfate alternatives tend to be larger molecules in general, they rank higher on the gentle end and lower on the cleansing end. This requires more total surfactant in the shampoo than in a sulfate-free shampoo to get the same amount of cleaning (in general >20% total surfactant vs. ~15% surfactant of a sulfate shampoo). This greater concentration of surfactants in shampoos can have the reverse effect on mildness of the formula, causing dryness.
So net, mildness of a shampoo formula or gentleness to color-treated hair cannot be determined by an ingredient statement. Instead, consider the brand, the amount of moisturization and wet protection you get from the sulfate-free shampoo to determine if its right for you.