Sodium Lauryl Sulfate

Sodium Lauryl Sulfate is the cleanser that users of CurlsBot worry about the most. When we think of "sulfates = bad" we're likely thinking of Sodium Lauryl Sulfate, commonly appreviated as SLS. But does SLS deserve it's bad reputation?

What is Sodium Lauryl Sulfate?

Sodium Lauryl Sulfate (SLS) is one of the most common detergents used in hair care products, though due to consumer concerns, it's used less and less.

SLS is a detergent, which means it cleans by breaking down oils, grease, and dirt, and suspending them in water for removal. Getting more scienecy, it's a anionic surfactant. A surfactant is a cleanser that has two components: a water loving (hydrophilic) head and a water hating (hydrophobic) tail. The head helps it mix with water. In chemistry, opposites attract. So because the tail has a negative charge, it attracts positively charged particles like dirt and oil. These dirty particles get washed off when you rinse your hair.

The reason SLS is used in shampoos is that is a very effective, cheap cleanser that works well even in hard water. It also lathers quite a lot, which people tend to like in shampoos.

Why do people with curly/wave hair avoid Sodium Lauryl Sulfate?

SLS's cleansing abilities sound great right? Who doesn't want to get rid of dirt? But it's the oil part that many curly/wave haired people worry about. Not all oils are bad. The natural oils in your scalp and hair help keep it shiny and healthy. And SLS can strip those away as well.

In the movement to better take care of curls, curl advocates like Lorraine Massey recommended avoiding sulfates like SLS in her famous book Curly Girl: The Handbook.

Your hair, on the other hand, needs to retain its natural oils to protect it and your scalp. Stripping them away deprives the hair of necessary moisture, amino acids, and antibodies, and makes it look dry, dull, and lifeless.

Pure SLS is also quite irritating for the skin, which also has an oily natural barrier. Disrupting this barrier can cause long-term inflammation.

As if that weren't enough, SLS got a bad rap in the 1990s due to claims around sulfates causing cancer. These claims have been disproven, but the bad reputation still lingers in the "clean beauty" community.

Sodium Lauryl Sulfate vs Sodium Laureth Sulfate

Don't mix Sodium Lauryl Sulfate (SLS) up with Sodium Laureth Sulfate (SLES), which is a similar slightly milder detergent. The reason SLES is considered milder is that it has some extra stuff added to the water loving head, which makes it more likely to hang out with water and the stuff in water than mess around with your skin.

What Do Hair Experts Say About Sodium Lauryl Sulfate?

Our table looks at references from various sources to see what they have to say about Sodium Lauryl Sulfate.

In general most cosmetics chemists and dermatologists agree that it's safe in proper formulations. Curly hair dressers and authors usually recommend avoiding it.

As always, the boring truth is that it depends on the formulation. There are lots of ways the SLS can be used in ways that aren't drying or irritating. Lab Muffin has a great explanation of how in some cases SLS can be gentler than other sulfate-free cleansers.

Our conclusion is that it's definitely not unsafe, but with all the great alternatives out there, if your hair is prone to being dry or your skin is sensitive, it can make sense to avoid it. Because so many respected experts in the curly hair community recommend avoiding it, CurlsBot puts a warning on products that contain it.