Sodium lauryl sulfate — SLS — is the primary cleansing agent in most commercial bar soap, body wash, shampoo, and toothpaste. It works. It also strips skin more aggressively than necessary for everyday cleansing, and it is one of the more commonly cited causes of irritation for people with sensitive or reactive skin.
Here is what SLS is, what it does, and why some people are better off without it.
What SLS Is
Sodium lauryl sulfate is a synthetic surfactant — a surface-active agent that reduces the surface tension between water and oil. In practical terms, this allows it to emulsify oils and lift them away from surfaces, which is the mechanism behind cleaning.
Despite being marketed under names that suggest a natural origin — it is sometimes described as "coconut-derived" or "plant-based" because it can be synthesized from lauric acid found in coconut or palm oil — SLS is the product of an industrial chemical process. The coconut oil connection is a distant one. The final compound is a synthetic surfactant.
Why SLS Is in Almost Everything
SLS is cheap, effective, and stable. It produces abundant lather, removes oil efficiently, and works across a wide pH range. From a manufacturing standpoint, it solves the problem of making an inexpensive product that cleans effectively and feels like it works (the foam is part of how consumers perceive cleansing performance).
The alternative — genuine soap made through saponification of oils — costs more to produce, has a shorter shelf life, produces less dense foam, and requires more careful formulation to balance cleansing and conditioning. For mass-market manufacturing, SLS wins on nearly every practical dimension.
What SLS Does to Skin
SLS is a more aggressive cleanser than the fatty acid salts produced by saponification. It disrupts the stratum corneum — the outermost layer of the skin — and breaks down lipids in the skin barrier more thoroughly than gentle surfactants do. For normal skin in good condition, the barrier repairs itself quickly after washing. For compromised or sensitive skin, the disruption compounds existing problems.
Research on SLS consistently shows it as an irritant at concentrations found in consumer products, particularly with repeated daily exposure. The effect is cumulative — daily use of SLS-containing products can maintain a state of low-level barrier disruption that manifests as dryness, tightness, or increased reactivity over time.
People with eczema, contact dermatitis, rosacea, or dry skin are more likely to notice the effect of SLS because their skin barrier is already compromised. Removing SLS from the daily routine — particularly in rinse-off products like soap — is one of the more consistently effective adjustments for people managing sensitive or reactive skin conditions.
What Natural Soap Uses Instead
In soap made through saponification, the cleansing agents are the fatty acid salts produced when oils react with lye. These are structurally different from synthetic surfactants like SLS — they are gentler on the skin barrier, less disruptive to natural lipids, and produced through a process that simultaneously creates glycerin, which remains in the bar and provides a conditioning effect.
Natural soap lathers differently than SLS-based products. The foam is real and effective, but it is not the dense, abundant lather that SLS produces. If lather volume is your primary measure of cleansing performance, natural soap will feel different. If skin comfort is the measure, the results tend to speak for themselves.
The Ingredient List Test
Find "sodium lauryl sulfate" or "sodium laureth sulfate" on a soap label and you know the product is a synthetic detergent bar. The absence of these entries — combined with the presence of saponified oils — tells you you are looking at genuine soap.
The No. 3 Bar contains no SLS, no SLES, and no synthetic surfactants of any kind. Three saponified oils. Nothing else. See the No. 3 Bar.