Jan 04,2023

A refreshingly cool bath in the summer is as enjoyable as a steamy soak in the winter. But maybe you’ve heard that bath bombs won’t work in cold water. It’s understandable that you don’t want to waste these delightful treats, so you need to know if this is true or not.

Technically, bath bombs do work in cold water because the reaction between baking soda (aka sodium bicarbonate) and citric acid still takes place. However, the fizzing reaction is so much slower in cold water that it may seem as if it’s not working. When making DIY bath bombs, you can adjust the ingredients to adapt them to react more rapidly in cold water.

How Do Bath Bombs Work?

Let’s discuss the chemistry behind bath bombs, how this is influenced by temperature, and how to make your bath bombs more reactive in cold water.

Primary Bath Bomb Ingredients

Bath bombs contain three primary ingredients. These are baking soda, citric acid, and cornstarch.

These ingredients are inert in their unused forms, which is why a bath bomb can be produced without immediately dissolving into a frothy fizz.

Chemistry Equals Fizziness

The fizzing of a bath bomb is attributable to an acid-base chemical reaction between the basic baking soda and the acidic citric acid. This reaction is triggered by the addition of water.

In water, the baking soda and the citric acid dissolve into reactive ionic components and interact with each other in a two-part reaction. When combined, the baking soda, citric acid and water release carbon dioxide and sodium citrate. It’s the carbon dioxide that is the star of this show.

Carbon dioxide is a gas at normal temperatures. So, when it is produced by this reaction in the bathwater, it rises to the surface and escapes into the air in rapidly forming bubbles—or bath bomb fizz. It’s essentially carbonating your bath water and turning it into a soda of sorts.

Bath Bombs Work in Cold Water…But Slowly

In a cold bath, the rate of reaction may be so slow with so little carbon dioxide gas being produced over time that it looks as if there is no reaction happening at all.

Sometimes, cool water will still yield a noticeable fizz reaction, but it will not be as satisfactory as a hot water reaction, and the bath bomb products can clump on the surface, which doesn’t look or feel so lovely.

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