At the pharmacy, people ask for it this way: “I need soap-free soap.” The name sounds like a play on words, but it is actually the most precise definition for this category of products.
It’s a bar, shaped like a bar of soap and used in the same way, but chemically it isn’t soap. The technical term is syndet, from the English synthetic detergent.
Traditional soap is a salt of fatty acids and produces highly alkaline solutions in water. Soap-free soap is made with synthetic detergents and has a pH of around 6-6.5 in solution. Everything else follows from this.
Article written by Elisa Avalle, founder of LeLang Skin Care and dermocosmetics specialist. Cover image generated with the support of artificial intelligence.
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Why it’s called soap-free soap
The name arose from a real commercial need. Calling it a “synthetic cleanser” on the shelf wouldn’t have worked, while calling it “soap” would have been inaccurate: in technical terminology, soap is a specific thing, namely the product of saponifying a fat.
So the descriptive formula has stuck: it looks and is used like soap, but shares neither its chemistry nor its pH. On labels and in scientific literature, you’ll find it called a syndet or a dermatological cleansing bar.
What is soap, chemically speaking?
Soaps are salts of fatty acids of animal or plant origin. Technically, they are anionic surfactants, the same family that forms the foaming base of most liquid cleansers, but with one distinguishing characteristic: in solution, they are highly alkaline.
A typical formula contains a significant amount of sodium stearate, semi-refined coconut or palm oils, sodium laurate, which provides foaming power, titanium dioxide or kaolin for an opaque white appearance, plus antioxidants, EDTA as a chelating agent, colorants, and fragrance.
They are not all the same:
- Marseille soap is the most traditional type: very hard and long-lasting, but precisely for this reason, it is not suitable for every skin type.
- Glycerin soap is transparent and less drying.
- Oily soaps, enriched with lanolin derivatives, lecithin, or sweet almond oil, reduce the irritation caused by other soaps.
What is a soap-free cleanser?
Dermatological cleansing bars are formulated with mild anionic synthetic detergents, such as alkyl sulfosuccinates, combined with amphoteric surfactants such as cocamidopropyl betaine.
These active ingredients have two technical advantages. They are not susceptible to hydrolysis, so the formula remains stable over time, and in solution they have a pH of around 6-6.5. They also contain opacifiers, plasticizers, colorants and fragrances. These are the products used to cleanse sensitive skin.
I've written a dedicated guide to surfactants in cosmetics, covering the different surfactant families and how to identify them in the INCI list.
Why pH changes the result
Healthy skin's surface is slightly acidic, and that acidity is no mere cosmetic detail: it helps control the resident flora and supports the enzymes that regulate shedding and cohesion in the stratum corneum.
A highly alkaline cleanser temporarily shifts that value. On healthy, young, intact skin, the return to baseline occurs without any obvious consequences. On dry, mature or already reactive skin, the same shift, repeated every day, compounds lipid depletion and causes that tight, flaky feeling.
The full explanation is in the article dedicated to skin pH, and the overall picture of cleansing mechanisms is in the guide to skin cleansing.
How to identify them on the label
The distinction is clear from the INCI list, without the need for testing.
- If you see ingredients such as Sodium Palmate, Sodium Cocoate, Sodium Olivate or Sodium Tallowate, you're looking at a soap: these are fatty acid salts obtained through saponification.
- If instead you find Disodium Lauryl Sulfosuccinate, Sodium Cocoyl Isethionate or Cocamidopropyl Betaine, you're looking at a soap-free cleanser.
- The wording on the front of the package isn’t a reliable guide. “Gentle soap” or “natural cleanser” tells you nothing about the pH of the solution.
When soap works just fine
There’s no reason to demonize it. On healthy skin without any particular sensitivities, a good-quality soap used on the hands and genuinely dirty areas causes no problems, and its degreasing power is a real advantage.
There are three situations where the picture changes: when skin is dry or atopic, when it’s reactive, and when you use a cleanser every day over your entire body. In those cases, a soap-free cleanser is the more sensible choice; if your skin is particularly reactive, go one step further and switch to shower oil, which leaves a more nourishing film and produces little foam.
If you’re not sure which situation applies to you, start by distinguishing dry skin from dehydrated skin and understanding the causes of skin sensitivity.
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What about shampoo?
The scalp is skin too, with a slightly acidic surface. That’s why shampoos are formulated with synthetic surfactants, and their pH is adjusted with weak acids, such as citric or lactic acid, usually to between 5.5 and 6.5: alkaline soap would make hair rough and dull, especially in hard water.
Even shampoos vary widely in how gentle they are. Those designed for frequent use contain mild surfactants, such as isethionates, glucosides, and betaines, and are the right choice for a dry or reactive scalp. Baby shampoo, often chosen because it’s “gentle,” is formulated not to irritate young children’s eyes and has a pH closer to neutral: it isn’t designed for an adult’s scalp.
If your scalp itches or flakes, it’s worth figuring out what’s going on before changing shampoos: we discuss it in our guides to an itchy scalp and dry or oily dandruff.
The issue is even clearer when it comes to the face
The skin barrier on the face is thinner and exposure to the environment is constant, so daily use of an alkaline soap is hard to justify. Here, the more suitable cosmetic formats are cleansing mousses, gels, and milks formulated with amphoteric and nonionic bases.
For guidance on the right sequence and when double cleansing makes sense, see my guide to double cleansing.
The limits of cosmetic advice
Changing your cleanser can address a tolerance issue, not a medical condition. If you have persistent redness, itching, lesions, pronounced flaking, or maceration in skin folds, you should consult a doctor or dermatologist. Only a diagnosis can determine whether cleansing is a contributing factor or simply something that makes another issue more visible.
At LeLang partner pharmacies and para-pharmacies, the first thing we look at when skin reacts isn’t the moisturizer, but the cleanser: it’s the product that comes into contact with the entire skin surface every day.
Not sure if your cleanser is right for your skin?
In a free virtual consultation, we’ll look at the INCI list of the product you’re using together and check whether it’s the right choice.
On the website: Facial cleansers · Sensitive skin · Body skincare
Frequently asked questions
What is soap-free soap?
Soap-free soap, also called a syndet or dermatological cleansing bar, looks and is used like a bar of soap, but chemically it is not soap. It is formulated with mild synthetic anionic cleansers, such as alkyl sulfosuccinates, combined with amphoteric surfactants such as cocamidopropyl betaine. In solution, its pH is around 6–6.5, whereas traditional soap produces highly alkaline solutions.
What is the difference between soap and syndet?
Soap is a salt of fatty acids produced by saponifying animal or vegetable fats, and is highly alkaline in water. Syndet uses synthetic surfactants that do not undergo hydrolysis, so the formula remains stable over time, and works at a pH close to that of the skin. On healthy skin, the difference is barely noticeable; on dry or reactive skin, you feel it every day.
How can you identify a soap-free cleanser on the label?
Just read the INCI. Ingredients such as Sodium Palmate, Sodium Cocoate, Sodium Olivate, or Sodium Tallowate indicate soap, as they are salts of fatty acids. Disodium Lauryl Sulfosuccinate, Sodium Cocoyl Isethionate, or Cocamidopropyl Betaine, on the other hand, indicate a soap-free cleanser. Front-of-pack claims such as "gentle soap" say nothing about the pH the product reaches in solution.
Is traditional soap bad for the skin?
No, there's no reason to demonize it. On healthy skin without any particular sensitivities, a good soap used on the hands and genuinely dirty areas causes no problems, and its degreasing power is a real advantage. Soap-free cleanser is the more sensible choice for dry, atopic, or reactive skin, and for daily use over the entire body.
When does reactive skin require a dermatologist?
Changing cleansers addresses a tolerability issue, not a medical condition. If persistent redness, itching, lesions, marked scaling, or maceration in skin folds develops, consult a doctor or dermatologist. Only a diagnosis can determine whether cleansing contributes to the problem or merely makes something else more visible.
Sources for this article
- Ananthapadmanabhan K.P. et al. (2004). "Cleansing without compromise: the impact of cleansers on the skin barrier and the technology of mild cleansing". Dermatologic Therapy, vol. 17, suppl. 1, pp. 16-25.
- Mukhopadhyay P. (2011). "Cleansers and their role in various dermatological disorders". Indian Journal of Dermatology, vol. 56, no. 1, pp. 2-6.
- Ali S.M., Yosipovitch G. (2013). "Skin pH: from basic science to basic skin care". Acta Dermato-Venereologica, vol. 93, no. 3, pp. 261-267.
- Trueb R.M. (2007). "Shampoos: ingredients, efficacy and adverse effects". Journal der Deutschen Dermatologischen Gesellschaft, vol. 5, no. 5, pp. 356-365.
- Regulation (EC) No 1223/2009 of the European Parliament and of the Council on cosmetic products.
Elisa Avalle is the founder of LeLang Skin Care and specializes in dermocosmetics at the University of Barcelona.
