Frequently asked questions about how soap works
Sara IdenforsHere you will find answers to common questions about how soft soap and bar soap clean, why handwashing is recommended by public health authorities, and what laboratory tests show about VästerbottensSåpa's bar soap.
Are soft soap and bar soap the same thing?
No, but they are based on the same fundamental chemistry.
Both soft soap and bar soap are produced through a chemical process called saponification, in which fats or oils react with a base to form fatty acid salts. These fatty acid salts act as surfactants and make cleaning possible.
The biggest difference is that bar soap is usually made with sodium hydroxide (NaOH), while soft soap is made with potassium hydroxide (KOH). Despite this, they clean according to the same chemical principle.
How does soft soap actually clean?
Soft soap cleans with the help of surfactants.
Surfactants have a water-loving (hydrophilic) part and a fat-loving (hydrophobic) part. When soft soap is mixed with water, small structures called micelles form. These surround grease, dirt, and many microorganisms so they can be rinsed away with running water.
The CDC explains that soap, together with water, lather, and mechanical action, traps and removes dirt, chemicals, and microorganisms from the skin.
Does soft soap kill bacteria?
The most important function of soft soap is to remove bacteria, dirt, and other microorganisms from the skin by loosening them and rinsing them away.
This differs from alcohol-based hand sanitizer, which primarily works by inactivating many microorganisms directly on the skin.
Is soft soap better than hand sanitizer?
It depends on the situation.
For the general public, the CDC recommends washing hands with soap and water in most everyday situations. If soap and water are not available, alcohol-based hand sanitizer containing at least 60% alcohol is recommended as an alternative.
Why are soap and water recommended?
Soap and water remove dirt, grease, and many types of microorganisms from the skin.
The CDC describes handwashing as the best way to remove germs and other contaminants in most everyday situations.
Is antibacterial soap better than regular soap?
Not for most users.
The CDC states that studies have not shown any additional health benefit from antibacterial soap compared with regular soap for the general public. Therefore, regular soap or soft soap is sufficient in most situations.
How long should you wash your hands?
The CDC recommends washing your hands with soap and water for at least 20 seconds.
This gives the surfactants and mechanical action time to loosen dirt and microorganisms before they are rinsed away.
Why is running water important?
Once dirt and microorganisms have bonded to the surfactants, they need to be rinsed away.
That is why handwashing consists of three parts:
- Soap or soft soap.
- Mechanical action (scrubbing).
- Rinsing with running water.
All three steps contribute to cleaning.
Can bacteria grow in solid soap?
RISE Research Institutes of Sweden investigated precisely this question.
In the laboratory, the bacterium Escherichia coli (E. coli) was added to diluted solid soap. After seven days, the bacterial count had decreased from approximately 1,700 bacteria/ml to less than 1 bacterium/ml.
RISE concluded that the tested solid soap did not promote bacterial growth under the conditions investigated.
Does that mean the soft soap is a disinfectant?
No. RISE's report shows how the tested product affected the bacterium studied (E. coli) under specific laboratory conditions.
The report does not show that the product:
- kills all bacteria,
- kills viruses,
- acts as a disinfectant,
- or has been tested according to standards for disinfectant products.
What is water activity (aw)?
Water activity is a measure of how much free water is available to microorganisms.
RISE measured the water activity in Soapa's solid soap as part of the laboratory investigation before conducting the microbiological test.
Why did RISE measure water activity?
Water activity can affect microorganisms' ability to grow.
However, RISE concluded that water activity alone could not explain the result. A microbiological test with E. coli was therefore also conducted.
What does surfactant mean?
A surfactant is a substance that can bind to both water and grease.
That is why surfactants are used in products such as soap and soft soap. They help loosen grease, dirt, and many microorganisms so they can be rinsed away with water.
Do bar soap and liquid soft soap work in the same way?
Yes, essentially. Both bar soap and soft soap contain fatty acid salts that act as surfactants. The main differences lie in their composition and manufacture, but the basic cleaning mechanism is the same.
Where can I read the laboratory report?
RISE's report on the solid soap is available as a PDF and describes the test method, water activity, microbiological test, and the laboratory's conclusions. Publishing the report alongside the articles allows readers to review the results and method themselves.
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