What Makes Soap Lather – The Science, History, Benefits, and Sustainability

Quite regularly we will get feedback, questions or even complaints from our customers regarding their soap, or soap flakes, not lathering. So what better place to explore and explain this than here! 

For many of us, lather is part of what makes soap feel “effective.” But what really causes soap to lather, and is more lather always better? To answer that, we are going to explore the chemistry, history, and sustainability behind those bubbles.

At its simplest, soap is made when oils or fats (like olive, coconut, or palm) are combined with an alkali (traditionally lye). This process, called saponification, creates soap and glycerin.

The molecules of soap have two parts:

• A hydrophilic head (water-loving)

• A hydrophobic tail (water-repelling, oil-loving)

When mixed with water, these molecules surround dirt and oils on the skin, allowing them to be rinsed away. As you rub the soap, air gets trapped with the soap and water mixture, forming bubbles — this is what we call lather.

Different oils affect the type and richness of lather:

• Coconut oil: produces big, fluffy bubbles.

• Palm kernel oil: adds stability to the foam.

• Olive oil: creates a creamier, lower-foam lather.

• Castor oil:  helps retain lather for longer.

So the basic formulation of a soap will determine how bubbly or creamy the lather feels.

Lather has always been associated with cleanliness and comfort. For centuries, people believed that the more foam a soap created, the better it must be at removing dirt. In reality, bubbles themselves don’t do the cleaning — it’s the chemical action of soap molecules.

Still, lather does have its benefits:

• Psychological reassurance: Foam makes us feel like the soap is “working.”

• Better coverage: Lather helps spread soap across skin and surfaces evenly.

• Pleasant sensory experience: Rich foam feels luxurious, soft, and indulgent.

• Practicality: In shaving soaps, for example, lather cushions the skin and razor.

It’s no surprise that soap makers, especially from the 19th century onwards, started designing formulas specifically for extra foaminess.

The downside is that modern consumers became conditioned to expect big bubbles — leading manufacturers to add artificial foaming agents particularly in products that are sold in countries with harder water like the UK.

Common examples include:

• Sodium Lauryl Sulfate (SLS)

• Sodium Laureth Sulfate (SLES)

• Cocamidopropyl betaine

These synthetic surfactants create dramatic foam but can strip natural oils from the skin, leaving dryness or irritation. In shampoos and body washes, sulfates are especially known for aggravating sensitive skin.

So while lather feels good, more bubbles don’t necessarily equal better cleansing — and in some cases, they may even cause harm.

You can read more on these ingredients here.

• Ancient soaps: The earliest soaps from Babylon (c. 2800 BCE) were simple mixtures of animal fats and ash. They produced little lather and were used mainly for textiles, not skin.

• Aleppo soap (Syria): Made with olive and laurel oils, Aleppo soap produces a creamy, low-lather wash. It inspired later Mediterranean soaps.

• Savon de Marseille (France): From the 17th century, Marseille became famous for cube soaps made with olive oil. These created a silky, modest lather prized for both laundry and skincare. Shop Traditional Marseille Soap Cubes here. 

• Industrial revolution: As soap became mass-produced, manufacturers used coconut and palm oils for their foaming qualities, catering to consumer expectations.

• 20th century & beyond: Synthetic detergents (syndets) took over, offering exaggerated lather at low cost — but at the expense of skin gentleness and environmental sustainability. Liquid soaps have the worst reputation but these ingredeints are present in most readily available bar soaps too. Browse gentle liquid soaps here

This history shows how our idea of “good soap” shifted from gentle creaminess to abundant foam.

Good, when:

• It’s created naturally by plant oils (like coconut, olive, shea).

• It helps spread soap evenly across the skin.

• It adds enjoyment to the washing experience.

Bad, when:

• It’s artificially boosted with harsh sulfates or petrochemical surfactants.

• It gives a false sense of “more lather = cleaner skin.”

• It causes dryness, irritation, or disrupts sensitive skin.

Ultimately, natural lather is harmless and beneficial — but artificial foaming additives should be approached with caution.

This brings us to an important modern question: how sustainable is lather?

1. Natural Oils vs. Synthetics

   • Traditional soaps made with olive, coconut, or shea butter are biodegradable and eco-friendly.

   • Synthetic surfactants (like SLS) can persist in waterways, harming aquatic ecosystems.

2. Consumer Habits

   • We often use more soap than necessary because of the belief that bigger lather = cleaner. This leads to waste.

3. Heritage Soaps

   • Marseille and Aleppo soaps show us that effective cleaning doesn’t require huge lather. Their low-foam, biodegradable recipes are models of sustainability.

When shopping for soap, ask yourself:

• Does this soap use natural oils for lather instead of synthetics?

• Do I really need lots of foam, or do I prefer a gentle, creamy wash?

• Is the soap biodegradable and eco-friendly?

• Does the brand have a tradition of sustainable soap-making (e.g., Provence or Aleppo)?

Soap lather is more than just bubbles —  While rich foam can feel luxurious, it’s not the measure of a soap’s quality or cleaning ability. In the UK our water is significantly 'harder' than in France so there will be quite a noticeable difference in the quantity of lather here to there, and also some variety from the same products when use from region to region within the UK.

• Natural lather, created by plant oils like olive and coconut, is gentle, effective, and sustainable.

• Artificial foaming agents deliver big bubbles but may harm both skin and the environment.

• Traditional soaps, like Marseille and Aleppo, remind us that sustainability and effectiveness don’t depend on excessive foam.

So next time you work up a lather, remember: the bubbles are part of the ritual, but it’s the ingredients behind them that truly matter.

Explore authentic, sustainable soaps from Provence and Marseille at frenchsoaps.co.uk