Sodium lauryl sulfate (SLS), also commonly known as sodium dodecyl sulfate, and sodium laureth sulfate (SLES) are widespread ingredients in personal care products. They can be found in cleansers (shampoo, soap, etc), toothpaste, mouthwash, and even cleaning products such as laundry detergent where they function as surfactants and foaming agents. A surfactant can be thought of as a detergent; chemically, this means a compound is composed of a water-loving portion and a lipid-loving portion, enabling it to wash away any dirt and oils with water. Though these ingredients are common, the phrase “sulfate free” may be equally so. Are these ingredients safe, or should you be on the lookout for these claims when buying your next product? What is the difference between these two similarly-sounding compounds? Are they safe for the environment? Continue reading to find out.

These naturally or synthetically derived ingredients may seem very similar in name and function, but they do differ. While their chemical structure is nearly identical, it differs by a single oxygen atom from SLES that is added during a process known as ethoxylation. This process results in the name change from lauryl to laureth, as well as other consequences involving the irritability and safety of these ingredients.

Both SLS and SLES are well-documented irritants to both the skin and eyes.[1] This irritation leads to skin redness and dehydration, as well as a change in the skin barrier function and the skin’s natural pH. The level of irritation that SLS causes is comparable to that of other surfactants; SLES, however, is less irritating than most. Products are often formulated to minimize this irritation (by adding additional ingredients or by lowering the concentration) and the final product is typically tested for overall irritancy.[2] Additionally, the degree of irritation will vary person-by-person, by the duration of contact with the skin (meaning if these ingredients are in your shampoo you are unlikely to experience this effect because you immediately wash them off, unlike a skin cream or lotion), and even by the time of year.[3] If you have dry skin, you are more susceptible to irritation from SLS and SLES. SLS is often used in irritation tests as a positive control, meaning it is used to purposefully cause irritation in order to compare the reaction level with other irritants. In these cases, SLS is used more to determine an individual’s propensity for irritation as not every individual will react.[4] If irritation to SLS occurs, irritation by other compounds is likely.[3]

Other concerns surrounding the use of these ingredients is whether or not they are carcinogenic and their effect on the environment. Neither SLS nor SLES is carcinogenic.[5] However, a byproduct produced during the ethoxylation process, 1,4-dioxane, is listed as being reasonably anticipated to be a human carcinogen by the National Toxicology Program.[5] Most manufacturers take measures to eliminate this contaminant from SLES, but some traces of it have been found in products.[6] The FDA reportedly monitors levels of 1,4-dioxane in cosmetics. However, it has set no recommended limits on the level of the anticipated carcinogen.[7] Although both SLS and SLES are biodegradable, they are considered moderately toxic to aquatic animals at high enough concentrations.[2] Luckily, these concentrations are likely never reached under present conditions due to the low amount present in products.

Bottom-line: if you have sensitive or dry skin, you may be better off avoiding products containing sodium lauryl sulfate. While sodium laureth sulfate is not as irritating, it may be best to avoid it as well if you have particularly sensitive skin. Otherwise, the use of either is safe, both for humans and the environment, so long as finished products have been properly monitored for levels of 1,4-dioxane.

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