Sodium lauryl sulfate

Chemical structure

Sodium lauryl sulfate (SLS) (or Sodium dodecyl sulfate) is a detergent, surfuctant, and foaming agent which is commonly used in a wide variety of cleaning products. SLS is a synthetic organic compound with the formula CH₃(CH₂)₁₁SO₄Na. It is composed of sulfuric acid, monododecyl ester, and sodium chloride (table salt). Since it causes skin irritation, it is often ethoxylated (by adding ethylene oxide) to reduce this effect. This results in the similar chemical Sodium laureth sulfate (SLES), the formula of which is CH₃(CH₂)₁₁(OCH₂CH₂).

Uses

As a cleaning agent, this is effective at penetrating and removing oils. It also helps its solution to spread across a surface. It is commonly added to liquid soaps, shampoos, detergents, toothpastes, mouthwashes, hair color and bleaching agents, body washes and cleansers, make-up foundations, laundry detergents, bath oils/bath salts, stain removers, carpet cleaners, fabric glues, shaving creams, and mascara.

In some cases, this substance is used primarily for its "foaming" property. Many manufacturers believe (and perhaps correctly) that consumers will like a cleaning product better if it "foams up," since it "really seems to be doing something." After using such products, those without it will tend to look less effective somehow. Sodium lauryl sulfate (or sodium laureth sulfate) is also helpful in liquid foam soap solutions, since they are turned to foam as they are dispensed. This chemical makes it foam much better than this soap would otherwise.

Toxicology

There are a number of health concerns regarding sodium lauryl sulfate. So far, the only scientifically proven problems it causes are skin irritation, desquamation of oral epithelium (shedding or oral tissue), and increased frequency of aphthous ulcers (canker sores). Some other points of concern are listed below.

• A common claim against sodium lauryl sulfate is that it is carcinogenic (cancer causing). This has not been scientifically proven, but testing in this area has been minimal. However, when ethylene oxide is added to reduce its irritative properties, the resulting sodium laureth sulfate is suspected to be carcinogenic. The ethylene oxide itself is a carcinogenic substance. Additionally, the ethoxylation process produces a byproduct known as "1,4 dioxane". This is recognized by the CDC to be "probably carcinogenic to humans," toxic to the brain and central nervous system, kidneys, and liver. As if this were not enough, 1,4 dioxane is also a leading groundwater contaminant.
• Another concern is rooted in the fact that SLS and SLES are not used by themselves. Rather, they are typically used in conjunction with other chemicals that can cause unwanted interactions. A chemical known as triethanolamine (TEA) is often used along with SLS and SLES, especially in shampoos. The sodium lauryl/laureth sulfate interacts with the TEA, and becomes NDELA (N-nitrosodiethanolamine). Unfortunately, NDELA is a nitrosamine, which is not only a potent carcinogen itself, but allso attracts nitrate, which is another carcinogen. Not only is this specific case a problem, but it is also evadance that the FDA simply cannot test all of the changes that may take place once SLS/SLES is put into use.
• Some argue that sodium lauryl sulfate is not a risk as much from a large, brief exposure (such as in laboratory experiments) but rather a small but continued exposure. Problems caused by this kind of risk are hard to track down, and even harder to test in a laboratory.
• While many people are not concerned about this chemical on the grounds that they are exposed to very little of it, the average dosage is actually surprisingly high. It is easily absorbed through the skin, which is where most of this product is placed. This along with the variety of other chemicals adds up to an shocking amount of absorption. For example, those who use conventional cosmetics on a daily basis, can absorb almost five pounds of chemicals and toxins into their bodies each year!

The concern is that as a surficant, SLS builds bridges between fat and water-soluble areas. This property of SLS may be disruptive of living cell membranes. The degree to which the human body can eliminate SLS has not been extensively studied, and SLS can be detected in a person five days after an exposure.