I talk a lot about the exceeding versatility of Dr. Bronner’s Castile Soap and Dr. Bronner’s Sal Suds. There are so many overlapping uses. But is there any time in which they aren’t interchangeable? Yes, but just a few.
Castile soap is primarily designed for the body. The blend of oils (coconut, olive, palm, jojoba, and hemp) are designed to be the most nourishing to our skin. But wait, there’s more. Because it is such a beautifully simple soap, it also cleans many other things amazingly well, whether it’s your dog, your sinks, or your floors. You can find details of all these uses on this Castile Soap Dilutions Cheat Sheet.
Because Castile soap is a true soap, it reacts with the minerals contained in hard water. (Here’s my test to find out if you have hard water.) The more dissolved minerals there are, the “harder” the water. The reaction of soap with these minerals in the water leaves behind an insoluble film that’s commonly called “soap scum”. This term is a bit of a misnomer, because it’s not actually soap that remains, but a precipitate of minerals.
You’ll only notice this on shiny objects that are left to air dry. They will take on a whitish film. (Read my post on eliminating soap scum.) Also, absorbent fabrics like towels and cloth diapers will become stiff and lose their absorbency. (But laundry in hard water is still doable – Read more here.)
Enter Sal Suds. This is our biodegradable household cleaner developed by my dad. Sal Suds doesn’t react with hard water. It rinses cleanly and leave surfaces sparkling. No more film on the tub or towels! For it’s multitude of uses, see the Sal Suds Dilution Cheat Sheet.
That’s all well and good, but I haven’t answered that initial question of what to use when.
Situations where I exclusively use Castile:
- Myself – Head to toe.
- My animals – Any Castile soap scent on my dog. Baby Unscented on my cat.
- Pest Control – Only Castile soap has this ability to eliminate insects.
Situations where I exclusively use Sal Suds:
- Most Laundry – sometimes, as with bedding, I use Castile soap.
Other than these few cases, I reach for whichever is closer at hand.
Now you know what to use, but perhaps you want to know why?
Soap and detergent are both surfactants. The word “surfactant” is a portmanteau of “Surface Active Agent.” If you’ve ever done a belly flop into a pool, then you’ve felt the power of surface tension. Surfactants break through the surface tension of water and make water really soak in.
My brother Mike says that:
Surfactants make water wetter.
The second magical power of surfactants is that they make oil and water coexist. Which they don’t otherwise like to do. This is why you can’t just rinse oil off your hands. The water runs over the oil like it’s just not there. And it just doesn’t care.
Now brace yourselves – you’re about to learn some Greek!
Surfactants solve the oil/water repulsion because one end of each surfactant molecule is hydrophilic and the other end is hydrophobic.
Hydrophilic literally means “water (hydro) loving (philic).” This end of the surfactant molecule grabs hold of water. On the other side, hydrophobic means “water (hydro) fearing (phobic).” A little exaggerated perhaps, but this end grabs the oil.
But we’re not talking about just one. Surfactant molecules work in groups. In a solution, they float around looking for oil molecules and snag with those hydrophobic tails, totally surrounding each oil molecule so there’s no part of the oil molecule left exposed to water. This little nugget is called a micelle.
The outside of this micelle is now entirely hydrophilic, which means instant attraction to the passing rinse water which carries it all away.
It’s like they’re filling those oil molecules with a whole lotta love and reaching out and connecting them with their former enemy, those water molecules. And once they’re connected, they realize it’s not so bad. They can get along. They can hang out together. I think there’s a larger lesson here.
You still with me?
So they’re both surfactants. Now for some differences.
Soap is close to nature, made by a beautifully efficient one-step reaction of combining oil (coconut, palm, olive, jojoba, and hemp for our Castile) with a strong alkali such as sodium or potassium hydroxide (the first also known as lye). Out of this combo, you get soap, glycerin and water. Bam! No leftovers. No waste. Beautiful.
Detergents are more complex and must be synthesized. They were developed during the World Wars when the oils needed for soap were scarce. They can start with botanical substances (such as coconut oil for our Sal Suds) or with petroleum derivatives. And the uses of detergents is vast and wide.
Tidy as it would be, I can’t sum it all up by saying, “Soap good. Detergent bad.” That would be a gross oversimplification. There are bad soaps (not ours, of course) that are poorly made with bits of unreacted alkali floating around in them ready to saponify your very body. You become walking bar of soap. Ouch!
And there are excellent detergents, such as our Sal Suds, which is super duper tough on grease and completely clean rinsing, yet mild and biodegradable.
So that’s a little bit more about the magic of cleaning and the beauty of chemistry.