Sulfates and Curly/Wavy Hair Guide

Sulfates are a top ingredient that people in the curly/wavy hair community worry about the most. But is their bad reputation justified?

What are sulfates?

Sulfates are a type of anionic surfactant, which is considered the strongest form of surfactant. As an ingredient, sulfates are primarily used for their cleansing properties and also because they create lots of nice lather, which people like even if it doesn't make a shampoo more effective.

Sulfates have a negatively charged hydrophilic (water loving) head that attracts positively charged oils and dirt, which are then rinsed off with the water ^[14]. That's great if it's oils you want to remove, and not so great if it's removing the hair and scalp's natural protective oils. Hair stripped of oils may feel dry and tangle more easily.

How do sulfates affect curly/wavy hair?

Sulfates potential negative effects on curly/wavy hair

Sulfate's potential to remove the scalp and hair's natural oils is why curl advocates like Lorraine Massey recommended avoiding sulfates like SLS in her book Curly Girl: The Handbook^[4].

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.

Another reason that some people with curly/wavy hair might avoid sulfates is that anionic detergents like sulfates can increase the presence of negatively charged particles in the hair which could lead to frizzy hair ^[14].

Finally, there is the concern that sulfates cause scalp irritation, which isn't specific to curly hair, but is one of the things brought up as a reason why people avoid sulfates. From a chemistry perspective, anionic surfactants can bind to our skin and damage the skin's barrier, leading to dryness. BUT that's as an isolated ingredient, not as a component in a shampoo. Studies that show sulfates are irritating are done in a laboratory setting with isolated cells in petri dishes or animals exposed to very large amounts of sulfates that you'd never encounter in a shampoo^{[15] [16]}. Unless you are allergic to sulfates, you probably don't need to worry about sulfates in shampoos irritating your scalp.

Sulfates potential positive effects on curly/wavy hair

There aren't any scientific studies I could find on the effect of sulfates on people with curly and wavy hair. Anecdotally, some people with curly/wavy hair find that sulfates make their hair look better. Especially for those with a weaker curl pattern, stronger deep cleansing shampoos with ingredients like sulfates can help remove build-up that weighs down their hair.

Personally, as someone with wavy mixed-porosity hair, I have a greasy scalp and dry ends. I've found that sulfate shampoo helps increase my hair's volume and I use it nearly every wash. I apply a "pre-poo" oil treatment to my ends to protect them and I focus the shampoo on my scalp.

Other people have found success with using sulfate shampoos as an occasional clarifying treatment once a month or every few weeks.

Different types of sulfates: SLS vs. SLES

Sulfates remain a complicated and controversial topic in the curly hair community. They aren't all the same. For example sodium laureth sulfate (SLES) has a larger hydrophilic head than sodium lauryl sulfate (SLS), which makes it gentler^[17].

Lab Muffin^[18] discusses why this is in her post on the subject:

The number of units can change, and this changes how the specific type of SLES interacts with everything else: water, oil and other surfactant molecules. Having these ethoxy units means less SLES will wander off on its own (and into your skin) compared to SLS.

The process is known as ethoxylation. She also notes that depending on the formulation, sulfate shampoos can be gentler than sulfate-free shampoos.

Another common group of sulfates are ammonium lauryl sulfate (ALS) and ammonium laureth sulfate (ALES) which are both considered less harsh than SLES for similar reasons (they are both ethoxylated) ^[19].

Should people with curly/wavy hair avoid sulfates?

As always, the boring truth is that how harsh sulfates are depends on the formulation^[20]. Shampoos aren't just made of one ingredient, they are made of a formula of many ingredients that work together. For example, most shampoos that contain sulfates also contain mild surfactants, conditioners, humectants, and more, which can balance out any negative effects of sulfates ^[21].

CurlsBot still warns people about sulfates in case they want to follow the curly girl method/cg method exactly, but as you develop your own routine, we encourage you to be open minded and see ingredients like sulfates not just as isolated chemicals, but as an ingredient in products that are part of a holistic haircare routine. You may find that a sulfate shampoo works great in your own routine, whether as an occasional clarifying treatment or as an everyday shampoo.