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Soap, syndets and sulphates: a plain guide to cleansers

· 2 min read

Every shampoo, soap, dishwash and detergent cleans with a surfactant: a molecule that grabs oil on one end and water on the other. The names on the label can look alarming. Here's what they mean, and what actually affects your skin.

Three families

  1. Soap. Oils reacted with an alkali, such as sodium hydroxide or potassium hydroxide. On a label, look for "sodium cocoate," "sodium olivate" or "saponified coconut oil." It's traditional and simple. It's also alkaline, at around pH 9–10.
  2. Syndets (synthetic detergents). Sodium cocoyl isethionate, sodium lauroyl methyl isethionate, cocamidopropyl betaine and sodium lauroyl sarcosinate are common examples. They're usually made from coconut or palm fatty acids, and they're designed to clean at a skin-friendly pH of around 5.5–7.
  3. Sulphates. Sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES). Strong foaming and cheap, and found in most mainstream shampoos and toothpastes.

"Synthetic" doesn't mean harsher

This surprises many people: for skin, mild syndets are generally gentler than traditional soap. Reviews of the research find that alkaline soap tends to disturb the skin's outer barrier more than a well-formulated syndet, especially for dry or sensitive skin. Some of this research comes from cleanser manufacturers, so we read it as a general consensus rather than a precise ranking. But it's why dermatologists often suggest "soap-free" cleansers for eczema.

So a shampoo bar made with sodium cocoyl isethionate isn't a compromise compared with a soap bar. It's simply a different approach.

Where sulphates come in

  • SLS is a known skin irritant at higher concentrations and with longer contact. A US expert panel found it safe in rinse-off products for brief use, and recommends low levels in anything left on the skin. Some people with sensitive skin or mouth ulcers prefer to avoid it.
  • SLES is milder than SLS, and isn't a skin allergen. Because it's made by a process called ethoxylation, it can carry tiny traces of 1,4-dioxane, which IARC lists as "possibly carcinogenic" (Group 2B). Manufacturers can strip it out, and New York now caps it at 1 part per million in personal-care and cleaning products. It's a quality-control issue, not a reason for alarm.

What makes a cleanser gentle

More than the surfactant family, it's:

  • concentration (how much),
  • contact time (rinse-off versus leave-on),
  • pH,
  • what else is in it (fragrance and preservatives are more common allergy triggers than surfactants),
  • your own skin.

Home cleaners

For dishwash and laundry, plant-derived syndets are common in "natural" brands, and that's fine. India's standards also limit phosphates in detergents, because phosphates feed algae in rivers and lakes. That's an environmental problem, and well documented.

How Everykind labels it

We don't mark mild syndets as a downside, because the evidence doesn't support it. Our amber "Sulphates (SLS/SLES)" tag appears only when a product contains SLS or SLES. None of our current picks do.

Sources

This is a summary of published research, not medical advice. Related tags on our standard: Sulphates (SLS/SLES).