Natural Bar Soap vs. Commercial Soap: What the Evidence Shows

Here is something most people do not know: many bars sold as "soap" are not soap in the legal sense. The FDA defines soap very narrowly, and the difference is real chemistry. But does it change how a bar behaves on your skin? The honest answer is not what most natural-soap marketing says.

The Chemistry Difference

What the FDA calls soap

The FDA says a product counts as soap only if it is "composed mainly of the 'alkali salts of fatty acids'," and those salts must be the only thing that does the cleaning. Many body cleansers, it says, "are marketed as 'soap' but are not true soap according to the regulatory definition." These are made with synthetic cleansing agents and are called syndets (short for synthetic detergents). The FDA adds that a product that is not true soap can still use the word "soap" on its label.

True soap is regulated by the Consumer Product Safety Commission, not the FDA. Everything else is regulated as a cosmetic.

How soap is made

Soap is made by mixing fats or oils (olive, palm, coconut) with a strong alkali such as lye. A published review describes it as saponification, and says the reaction creates soap and glycerol. Syndets are made by other chemical processes. That is the whole "natural vs. commercial" split, and it is about the method and the cleansing agent, not about whether the oils are plants.

What the Research Says About Skin

This is the part that natural-soap marketing tends to skip.

• pH: one review puts soap at a typical pH of 8.5 to 11, while skin is around 4 to 6 and syndets are 5.5 to 7. A 1995 review says syndets with a pH near 5.5 "do not interfere with the cutaneous microflora" (the normal bacteria on skin), unlike alkaline soap.
• Barrier and dryness: a 2022 review says soap "tends to negatively affect the skin by causing barrier disruption, lipid dissolution and pH alteration," while syndets can maintain the skin's structure. A 2018 review says syndets have "lower skin irritation and dryness." A 1987 review says soaps are "generally quite irritating while syndets can range from mild to harsh."
• Marketing: the 2022 review even says soap is often preferred "possibly due to the negative connotations around anything that is not perceived as natural."
• Commercial soaps are not all the same: a lab study of 22 commercial products sold as soap (bar soaps and liquid hand washes) measured pH from 7.01 to 10.17.

How much weight to give this

Be fair to both sides. The 2022 review comes from researchers at a company that makes syndet cleansers. The 1987 review is old. And these are reviews of cleanser science in general, not a head-to-head test of a handmade bar against a store-bought bar on men's skin. We did not find one. What we can say is that none of the sources we read supports the idea that natural soap is gentler than a mild syndet. Several lean the other way.

Also remember that both groups include harsh and mild products. "Syndet" does not guarantee gentle, and neither does "natural."

Glycerin

Glycerol forms when oils turn into soap, according to the soap-making review. Many natural-soap brands say they leave it in, and that commercial makers take it out and sell it. We could not find a reliable source that confirms that claim, so we cannot tell you whether a specific commercial bar has less glycerin. What we do know is from the 1987 review: glycerin added to a bar has "little effect" on how irritating it is, because very little is left on your skin after you rinse. So glycerin alone is not a reason to switch.

Fragrance

Both kinds of bars can contain fragrance. The FDA says fragrance can be listed as just "Fragrance" and that its formulas can be kept as trade secrets, so a single word may hide many ingredients. Natural bars often use essential oils instead, which are easier to look up. But a 2025 review says fragrances and essential oils are the main allergens in cosmetics, and that "natural" ingredients "may also be allergenic." If your skin reacts easily, "fragrance-free" is the safer label, whichever kind of bar it is.

Side-by-Side Comparison

When Either Is Fine

If you have no dryness, no reactions and no strong feelings about ingredients, you do not need to change anything. Choose the bar you like to use. Always keep showers short and rinse well.

If a bar leaves your skin tight or bothered, the research above is a reason to try a milder, near-skin-pH, fragrance-free bar, whether it calls itself natural or not. If dryness or irritation keeps coming back, see a doctor.

The Bottom Line

Natural soap and detergent bars really are different products. But the evidence we found does not say natural soap is better for your skin, and several sources say a milder detergent bar is easier on the skin barrier. Buy natural soap if you like the scent, the ingredient list or how it feels. Just do not pay extra on the assumption that "natural" means gentler.

Sources

1. FDA: Frequently Asked Questions on Soap
2. Skin Cleansing without or with Compromise: Soaps and Syndets (Molecules, 2022)
3. The science behind skin care: Cleansers (2018 review by Draelos)
4. The irritancy of soaps and syndets (Cutis, 1987)
5. The concept of the acid mantle of the skin: its relevance for the choice of skin cleansers (1995)
6. Heliyon 2025: lab study of 22 commercial soaps (bar soaps and liquid hand washes)
7. Environmental impact of increased soap consumption during COVID-19 pandemic: Biodegradable soap production and sustainable packaging (2021)
8. What is New in Contact Allergy To Cosmetics for Physicians, Cosmetologists, and Cosmetic Users? (2025)
9. FDA: Fragrances in Cosmetics