05/31/2026
Don't combine Epsom salt with Dr. Bronner's.
Use these two separately, not together.
For example, you could soak in a bath with Epsom salts, drain the tub, then wash with soap. Or the other way around: a quick wash, and then the soak. 😉
Our green cleaning expert, Going Green with Lisa Bronner, did a little chemistry dive into why:
1. Chemically, Epsom salts are magnesium sulfate. It's called an acidic salt because when it dissolves in water, it creates a slightly acidic solution with a pH around 6. Since soap is alkaline, when they're combined, the two create a small acid/base reaction.
2. Furthermore, and more problematically, magnesium itself is highly reactive with soap, bumping the sodium or potassium ion off the head of a soap molecule and taking its place.
This resulting magnesium soap is called lime soap, or more commonly "soap scum." Which means, in essence, combining Epsom salt with Castile Soap is a recipe for soap scum.
That's a problem. You don't want this on your bathroom fixtures and you don't want this coating your pipes.
Want a deeper dive into the chemistry behind the reaction? Click here to read Going Green with Lisa Bronner's thorough blog post: drbronner.net/epsomsalt
