The Science Behind Soap: How Does Soap Work on Your Skin?

Do you recall feeling like your hands were greasy or that your skin was oily as the day progressed? You’d quickly wash your hands with soap, and they’d feel clean instantly. However, do you understand how a bar of soap works?

Although you may think washing your face with soap is a straightforward task, it’s actually based on chemistry and the anatomy of your skin. Soap does not just wash away dirt off your skin; it also interacts with oil, water, and other microbes that cause pollution (dirt) and creates a physical connection that allows a good clean.

Understanding how a bar of soap works is not only essential to your understanding of the chemistry and anatomy involved, but it can help concentrate on maintaining healthy skin, as well. The soap you choose, the pH of your soap, and the water you are using in your home all play a role in the way it affects your skin barrier, hydration and overall comfort level of your skin.

Let’s explain the chemistry behind soap in a manner that will be easy to understand.

What Is the Purpose of Soap? What Does It Clean?

To understand the function of soap, let's examine what it cleans from skin daily.

Various substances accumulate on skin daily:

• Sebum (the natural oil produced by sebaceous glands),

• Sweat (comprised of water, salt and metabolic waste)

• Dirt and dust from the environment,

• Bacteria and other microorganisms,

• Pollutants and cosmetic residue.

The fact is: Water alone cannot wash away oil-based (lipophilic) substances.

Oil and water have different chemical structures, making them incompatible- so they do not mix. So while washing or rinsing with water will wash away some surface particles it does not completely wash away greasy, oily impurities.

By providing a connection between oil and water, soap allows to remove the oil from the skin while providing a means of rinsing off both the oil and all of the associated pollutants from our skin.

How Soap Actually Cleans Your Skin: The Science

Now to the main question: how does soap work at the molecular level?

Soap has an amphiphilic structure

The molecules in soap are amphiphilic, which means it has 2 distinct parts:

• Hydrophilic: This is the head which attracts water

• Hydrophobic: This the tail which attracts oil & grease

This duality makes soap effective.

Step-By-Step Process

• Binding to dirt or oil 

The hydrophobic tails of the soap attach themselves to the sebum, oil and other oil-like materials on our bodies.

• Formation of Micelles

The soap molecules surround these oil molecules and form tiny spherical structures called. The oil is trapped in these structures.

• Emulsification

This step causes the oil to break down into small droplets that can mix with water, or emulsify.

• Wash Away

By rinsing with water, the micelles containing the dirt, oil, and microbes are washed away.

• Analogy

Soap acts as a "mediator" between oil and water by using the hydrophobic tails to grab onto oil and the hydrophilic heads to grab onto water. So you can wash everything off of your skin.

The mechanism by which soap works is explained scientifically through amphiphilic action combined with micelle formation.

Balance Problems: Cleansing vs Stripping

An understanding of soap's role in skin cleansing highlights an important concern - not all cleansing supports skin health.

Skin Barrier Function

The skin barrier, also known as the stratum corneum, includes:

• Lipids (fats) to help retain moisture

• Natural moisturizing factors (NMFs)

• A  balanced microbiome

What Happens with Harsh Soaps?

Harsh soaps:

• Remove essential lipids

• Disrupt the skin barrier

• Increase transepidermal water loss (TEWL)

Common Effects

• Dryness and tightness

• Irritation or sensitivity

• Flaky or rough texture

• Increased oil production by the skin in reaction to being stripped of its protective oils

Thus, while it is necessary that we use soap to cleanse our skin, excessive and harsh usage can lead to over-stripping and compromise overall skin health.

pH Levels of Soap: Why It Matters for Skin Barrier

The pH of soap is another crucial component to understand how soap functions. 

Natural pH Levels of Skin

Your skin has a natural acidic pH level hovering between 4.5 and 5.5. This acidic layer can be referred to as an acid mantle. This layer:

• Protect against harmful microbes

• Support the action of enzymes that repair the skin's barrier

• Help maintain moisture in the skin.

Traditional Soap vs. the pH of Your Skin

Commonly, traditional soaps have an alkaline pH level of around 9-10, which creates the following potential issues:

• Disrupts the acid mantle in your skin

• Alter the skin microbiome

• Leads to dry or irritated skin.
  

  

pH-Balanced Cleansers

The pH-balanced cleansers available today, or syndets, work much closer to the natural pH of the skin and:

• Preserve the function of the skin's barrier

• Cause less irritation of the skin

• Keep the skin hydrated.

Thus, when looking at how soap functions, it is not just about cleanliness; it is about the maintenance of your body's physiological balance.

Hard Water + Soap = Skin Problems?

It is interesting to know that the quality of your water can affect your skin even if your understand how soap works.

What is hard water?

Hard water contains excess levels of minerals such as:

• Calcium (Ca2+)

• Magnesium (Mg2+)

What happens when soap comes in contact with hard water?

• Insoluble salts (soap scum) is formed when soap reacts with these minerals

• Decrease in lather formation

• Remains of residue on the skin

Effects on skin

• Roughness and dryness

• Irritation

• Cleansing efficiency is reduced

• Dull appearance

This exactly explains why your skin might feel less clean or slightly sticky when it is washed in hard areas.

High pH vs Low pH Soap

FAQs

1. How Does Soap Remove Bacteria? 

When soap removes bacteria it traps bacteria inside micelles and washes them away using water, rather than actually killing the bacteria. 

2. Is Soap Better Than Body Wash? 

Some body washes are pH balanced; therefore they are gentle on your skin than traditional soap since it is more alkaline. 

3. Can Soap Damage the Skin Barrier? 

Soap has the potential to damage skin due to overuse or being too harsh with a product. Soap will strip essential lipids and disrupt the acid mantle. 

4. What Is The Ideal pH For Soap? 

The best pH for a cleanser is close to that of the skin, approximately pH of 5.5. 

5. Why Is My Skin Dry After Washing? 

Dryness is caused by the loss of natural oils and increased amounts of transepidermal water loss. 

6. Will Soap Work In Cold Water? 

Soap will work in cold water, but not as well, oils will dissolve more readily in warm/hot water.

Conclusion

Learning how soap works shows us that cleaning isn't only about removing dirt and visible oil; there's a chemical action that removes oils, germs and dirt from skin. Figure out if soap and other factors (like water pH, formulation and water quality) will help or hurt your skin barrier.

The right product can help keep your skin healthy and strong as well as clean! For example, a gentle, pH-balanced cleanser will effectively clean your skin but won't strip your skin of important moisture.

Recommended Products by Blue Nectar:

Mridu Snan with Ghee Soap | pH Balance Soap with Kojic Acid, Glutathione & Glycerine | Gentle Cleansing Bar

Mridu Snan Baby Soap with Ghee & Coconut Oil for pH Balance| Tear Free Formula (150 g)

Related Articles:

The Evolution of Soap from Ash to Ayurveda: A Complete History of Soap

References:

https://www.britannica.com/story/how-does-soap-work

https://www.science-sparks.com/why-dont-oil-and-water-mix/

https://www.sciencedirect.com/topics/engineering/amphiphilic-molecule

https://hzo.com/blog/hydrophilic-hydrophobic-waterblock-technology-whats-difference

https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/emulsification

https://pmc.ncbi.nlm.nih.gov/articles/PMC10861303/

 https://www.researchgate.net/publication/266623508_Evaluation_of_pH_of_Bathing_Soaps_and_Shampoos_for_Skin_and_Hair_Care