Liquid vs. Bar Soap: The Chemistry Behind the Suds
It’s one of those surprisingly heated bathroom debates: is liquid soap better than bar soap, or is it the other way around? Some people swear by the convenience of a pump bottle, while others are fiercely loyal to a solid bar. At The Clean Chemist, we believe there’s only one way to settle the sudsy score: science.
In this post, we’ll break down the chemistry, sustainability, and skin science behind both types of soap so you can choose the best option for your skin and for the planet.
The Chemistry of Soap: A Quick Refresher
At its core, soap is chemistry in action. Whether it’s in a bar or a bottle, soap is made by combining fats or oils with an alkali — a reaction called saponification. The result? Soap molecules: tiny superheroes with a split personality.
One end loves water (hydrophilic).
The other loves oil (hydrophobic).
When you lather up, these molecules surround dirt and oil on your skin, forming micelles — microscopic bubbles that trap grime — and rinse it away.
Key takeaway: Both bar and liquid soaps clean the same way. The differences come down to formulation, packaging, and environmental impact.
Bar Soap: The Old-School Workhorse
Bar soaps are usually made from the sodium salts of fatty acids, such as sodium stearate, which give them their solid structure.
Because bar soaps contain very little water and have a naturally higher pH, they are generally preservative-free. This makes them simple, long-lasting, and naturally resistant to microbial growth.
However, if a bar sits in standing water, it can become soft or even start to melt. Pro tip: Store your soap in a well-drained dish to keep it firm, dry, and long-lasting.
Liquid Soap: The Pumpable Powerhouse
At The Clean Chemist, we craft true liquid soaps—like our Hibiscus Palm—using the potassium salts of fatty acids diluted in water. Chemically, they’re very similar to bar soaps, which are made from the sodium salts of fatty acids. Both are considered true soaps, and both are naturally alkaline, with a pH around 9 or 10.
Because true liquid soaps contain more water than bars, they need preservatives to prevent bacteria and mold growth. That added water also means heavier packaging, higher shipping costs, and greater energy use compared to bar soap production.
It’s also worth noting that many products marketed as “liquid soap” aren’t actually soap at all. They’re synthetic detergent cleansers, or syndets, made through a different chemical process. Syndets can be formulated with a lower pH that’s closer to your skin’s natural balance and can come in either bar or liquid form.
The important takeaway:
Our Hibiscus Palm and other liquid soaps are true soaps, naturally alkaline, and clean the same way bar soaps do.
Syndet cleansers are an entirely different category and are often labeled “pH balanced” or “gentle cleansers.”
Is One Cleaner Than the Other?
Here’s a common claim: “Bar soap is covered in bacteria . Liquid soap is cleaner.”
Sounds logical… but the science tells a different story. For bacteria and mold to grow, three things are usually needed:
Water — microbes need a moist environment.
Food — something organic to feed on, like oils, skin cells, or sugars.
Time + temperature — warm, damp conditions speed things up.
Now here’s the twist: liquid soap actually checks more of those boxes than bar soap. Because liquid formulas contain a lot of water, they create an environment where bacteria could thrive unless we add preservatives. That’s why every reputable liquid soap includes preservatives or antimicrobial agents to keep it safe.
Bar soaps, on the other hand, are solid and low in water, which makes them naturally resistant to microbial growth. While it’s true that bacteria can land on a bar’s surface, studies show that these microbes don’t typically transfer to your hands in meaningful amounts.
Pro tip: To keep your bar soap in top shape, let it dry between uses in a well-drained dish. Not only does this keep the bar firm and long-lasting, but it also minimizes surface moisture — giving microbes even fewer opportunities to hang out.
Bottom line: Neither bar nor liquid soap is inherently “cleaner.” Both work equally well to remove dirt, oil, and microbes when used properly. The difference lies in how they’re formulated and stored.
The Environmental Impact
When it comes to sustainability, bar soap generally has the advantage. The differences aren’t just in packaging but also in how each product is formulated and transported.
Packaging
Bar soaps are often sold with minimal or plastic-free packaging, making them a lower-waste option. Liquid soaps, on the other hand, almost always come in plastic bottles that eventually end up in recycling streams or landfills.
Transportation
Liquid soaps are mostly water, which makes them heavier and bulkier to ship. More weight and larger packaging mean higher transportation emissions. Bar soaps are lighter and more concentrated, so they have a smaller carbon footprint.
Production Energy
Producing liquid soap typically requires more energy, especially when you account for water purification and the manufacturing of plastic bottles.
Switching from liquid to bar soap can make a measurable difference. Some studies estimate that choosing bar soap over liquid can reduce household plastic waste by as much as 90 percent.
At The Clean Chemist, we pack our liquid soaps in glass containers as much as possible to reduce plastic waste. However, glass does increase the weight of the packages being shipped, and therefore increases the energy required to ship them.
Skin Science: What Works Best for You
From a skin health perspective, there isn’t a universal winner. The best choice depends on your skin type, your preferences, and the ingredients in the product itself.
For Dry or Sensitive Skin
Liquid soaps are often formulated to be closer to skin’s natural pH and may include added moisturizers, making them a good choice for some sensitive skin types. However, a well-made, superfatted bar soap—like our Oatmeal, Honey & Milk Bar—can be equally gentle and nourishing.
For Oily or Acne-Prone Skin
Bar soaps with additives like charcoal or clays, such as our Carbon Theory soap, can help absorb excess oils. Gentle liquid cleansers designed for oily skin can also be effective; the key is choosing products without overly harsh surfactants.
For Fragrance Sensitivities
Unscented bar soaps often have simpler formulations and fewer potential irritants. Our Fragrance-Free Bar is designed with this in mind. Some liquid soaps also come in unscented versions, but check the label for hidden fragrance compounds if you’re sensitive.
The takeaway is simple: formulation matters more than format. A thoughtfully crafted bar or liquid soap will work well as long as it’s matched to your skin’s needs.
The Clean Chemist’s Perspective
When comparing bar and liquid soaps, the science makes it clear:
For sustainability: Bar soaps are typically the more eco-friendly option.
For customization: Liquid soaps allow for more additives, making them highly adaptable.
For skin health: Both can be excellent choices when well-formulated.
At The Clean Chemist, we focus on creating products that balance skin health, environmental responsibility, and ingredient transparency. Whether you prefer a bar or a bottle, you can trust that our products are free of phthalates, parabens, and other unnecessary additives, and are made with sustainability in mind.
Final Thoughts
Choosing between bar and liquid soap isn’t about which one “works better.” Both clean effectively when formulated and stored properly. The decision often comes down to environmental impact, personal preference, and skin needs.
If you’re curious, try experimenting for yourself. Compare one of our handcrafted bar soaps, like Spectral Shift or Lab Partner for Life, with one of our liquid soaps like Hibiscus Palm. Notice how your skin feels, how long the products last, and how much waste they generate.
At The Clean Chemist, we believe clean chemistry leads to radiant skin and a healthier planet. Knowledge is power, and bubbles are just a bonus.
