Sodium Lauryl Sulfate vs Soap: What Is the Difference?

If you have ever looked for "sulfate-free" products, you have met sodium lauryl sulfate (SLS). It is common in body washes, shampoos and toothpaste.

What SLS is

SLS is a synthetic surfactant, a detergent that lowers the surface tension of water so it can lift oil and dirt. It foams well and is inexpensive.

How it differs from soap

• Soap is made by reacting fats and oils with lye (saponification).
• SLS is a manufactured detergent, not soap.
• Soap is alkaline; SLS-based cleansers can be formulated at a lower pH.
• In the U.S., products cleaning mainly with detergents are regulated as cosmetics, not "soap."

Is SLS safe?

A safety assessment cited by Healthline found SLS safe in products that are rinsed off quickly, while recommending low concentrations in products left on the skin. It is a known skin irritant at higher exposures but is not considered a carcinogen.

SLS vs SLES

Sodium laureth sulfate (SLES) is a related ingredient that is generally milder than SLS.

Where you will find SLS

• Shampoos and body washes, where it creates rich foam.
• Toothpaste.
• Bubble bath and some hand soaps.
• Household cleaners and dish soap.
• Some solid 'shampoo bars' and syndet bars.

Other sulfate-free surfactants you will see

'Sulfate-free' products still need a cleansing ingredient. Common alternatives include:

• Sodium cocoyl isethionate (SCI): a mild surfactant often used in syndet bars and shampoo bars.
• Cocamidopropyl betaine: a gentle surfactant often paired with others to boost foam.
• Decyl glucoside and coco-glucoside: mild cleansers made from plant sugars and fatty alcohols.
• Sodium cocoyl glutamate: an amino-acid-based surfactant.
• True soap: sodium or potassium salts of fatty acids, such as sodium olivate.

How to read the label

Ingredients are listed in descending order, so if SLS or SLES appears near the top, it is a main cleanser. 'Sulfate-free' on the front only tells you what is missing, not whether the formula suits your skin. If you react to a product, note the first few ingredients and compare with others you tolerate well.

Is soap gentler than SLS?

It depends. Soap is alkaline, which some people find drying, while SLS can be irritating at higher concentrations. Many people do well with either. Syndet cleansers based on milder surfactants, such as SCI, are often the gentlest option for sensitive skin. See soap pH explained and bar soap vs body wash.

Not sure whether your cleanser contains SLS or real soap? Paste the ingredient list into our soap label decoder and it will tell you.

Who might want to avoid it

• People who find SLS products drying or irritating.
• People with sensitive skin or eczema who notice flare-ups.
• Anyone who simply prefers a short, soap-based ingredient list.

Prefer a true soap? Start with what is castile soap.