Short answer

Soft soap and bar soap are based on the same fundamental chemistry. Both contain fatty acid salts that function as surfactants – substances that bind to both water and grease. When hands or surfaces are washed, grease, dirt, and many microorganisms are released from the underlying surface and rinsed away with running water.

That is why international public health authorities such as the CDC recommend washing hands with soap and water as the first choice in most everyday situations. When soap and water are not available, alcohol-based hand sanitizer is recommended as an alternative.

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Soft soap and bar soap – the same chemistry

Although the words are often used as if they referred to different types of products, they are based on the same chemical principle. (Sweden is one of the few countries that has its own word for soft soap; many languages use the same word for all soap.)

Both bar soap and soft soap are formed through saponification, in which natural fats or oils react with a strong base to form fatty acid salts. These fatty acid salts are surfactants – the substances that make cleaning possible.

The main difference is the base used during manufacturing:

Despite these differences, both work according to the same fundamental cleaning mechanism.

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Why soft soap and bar soap clean

A surfactant molecule has two different ends.

• One part is attracted to water (hydrophilic).
• One part is attracted to grease (hydrophobic).

When bar soap or soft soap is worked into water, small structures called micelles form. The hydrophobic parts surround grease, oils, and other dirt, while the hydrophilic parts face outward toward the water.

The CDC explains that these micelles capture dirt, chemicals, and microorganisms. When the hands are then rinsed under running water, the contents are carried away. It is therefore the combination of surfactants, mechanical action, and rinsing that produces the cleaning effect.

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Why soap and water are recommended

During the COVID-19 pandemic, many public health authorities emphasized the importance of handwashing.

The CDC currently states:

"Washing hands with soap and water is the best way to get rid of germs in most situations."

The CDC also explains why:

• soap and water remove dirt and microorganisms from the skin,
• hand sanitizer is a good alternative when soap and water are not available,
• but handwashing works better when hands are visibly dirty or greasy.

It is important to distinguish between removing microorganisms and killing them. The primary function of soap is to help loosen and carry dirt and microorganisms away from the skin with the water.

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How does this relate to Västerbottenssåpa's bar soft soap?

International research explains how bar soap and soft soap clean.

RISE, on the other hand, investigated a different question:

Can bacteria grow in the bar soft soap between uses?

To answer this question, a microbiological laboratory test was conducted in which the bacterium Escherichia coli was added to diluted bar soft soap.

After seven days, the bacterial concentration had decreased from approximately 1,700 bacteria per milliliter to less than 1 bacterium per milliliter. RISE concluded that the tested bar soft soap did not support bacterial growth under the conditions examined and assessed that the product's high pH and water activity likely contributed to the result.

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Two different scientific questions

It is important to distinguish between two different types of research.

Question 1 – How do soft soap and bar soap clean?

There is extensive international research and guidance from organizations including the CDC describing how surfactants, mechanical action, and rinsing together remove dirt and microorganisms from the skin.

Question 2 – Can bacteria grow in the product itself?

That question is addressed by RISE's laboratory test of Västerbottenssåpa's bar soft soap, in which the bacterium tested, E. coli, did not grow under the conditions examined.

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Conclusion

Soft soap and bar soap are based on the same fundamental chemistry. Both contain surfactants that bind to both water and grease, allowing dirt and many microorganisms to be loosened and rinsed away with water. That is why international public health authorities recommend washing hands with soap and water as the first choice in most everyday situations. Västerbottenssåpa's own RISE report complements this knowledge by showing that the tested bar soft soap, under the laboratory conditions examined, did not support the growth of the bacterium tested, E. coli.

Sources:

• CDC – About Handwashing
• CDC – Hand Hygiene Frequently Asked Questions
• CDC – Handwashing Facts and Research
• RISE report on Västerbottenssåpa