Will a Bath Bomb Work in Cold Water?

colorful bath bombs

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?

bath bomb and cold water bath

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.

The Purpose Of Cornstarch In The Bath Bomb

The explosive fizziness of the bath bomb is part of the experience, but you don’t want it to be over too soon. This is where the cornstarch comes in. Cornstarch slows the reaction down to make it last longer.  

Bath Bomb Embeds

Make Your Bath Bombs Spin and Fizz Like Crazy

Many bath bombs contain an “embed” in the center. These are mini-bath bombs that are made only with citric acid and baking soda, but without the cornstarch. The embeds react more quickly than the bath bomb which contains it. The result is an extra fizzy, spinny bath bomb.

You can use embeds to make your bath bombs fizz and spin like crazy. But there’s a secret to how you place the embeds to create the most dramatic effect. Watch the video just above for details.

Heat Speeds Up the Bath Bomb Reaction

Summer Swim turns your bathwater into an ocean

Heat is one of the most common catalysts in chemistry. Catalysts are things that speed up the rate of a reaction. The reaction can take place without the catalyst but will do so at a much slower rate. 

So, heat catalyzes the reaction between baking soda and citric acid in the presence of water. But why?

Heat is energy. When you heat up the water molecules, you are giving them more energy. This energy makes them move faster and faster, increasing how often they bump into each other and any other substances are in the water. 

In this case, these other substances are baking soda and citric acid, and the impacts trigger the dissolution of these two ingredients into their reactive forms. 

As the reaction between these two bath bomb ingredients occurs more rapidly, carbon dioxide gas is produced more quickly, breaking down the bath bomb and causing the fizz. 

Even Air Can Make a Bath Bomb Work

As mentioned, heat is only a catalyst for the reaction between baking soda and citric acid in the presence of water. Without heat, the reaction will still take place, but at such a slow rate.

Even the water in the air will trigger a reaction. This why bath bombs sitting in the bathroom cabinet will lose their fizziness over time if they are not kept tightly sealed. Find out more about when unused bath bombs expire.

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. 

Secondary Bath Bomb Ingredients in a Cold Bath

Bath bomb ingredients - Carrier oils dilute essential oils and deliver them to the skin

Most bath bombs are not only made with baking soda, citric acid, and cornstarch. They usually have added, or secondary, ingredients such as essential oils, salts, butters, creams, etc. 

Bath bombs are typically designed to work in warm to hot water, so you need to consider how cold water will affect the secondary ingredients as well. While these secondary ingredients are wonderful to use in bath bombs dropped into a warm or hot tub, in a cold water bath you want to avoid them:

Avoid Bath Bombs With Lots Of Essential Oils

Essential oils are expensive, so they can increase the cost of a bath bomb. In a cold bath, the essential oils are not going to be released as well as they would be in hot water. Furthermore, there is no steam in which they can disperse. This means that you will largely lose the aromatherapeutic effects of bath bombs containing essential oils.

Don’t Use Bath Bombs That Contain Lots Of Salts

Many bath bombs contain salts. Epsom salts are very healing, but other bath salts with larger crystals like Himalayan and sea salt are also often used in bath bombs.

When you put a salt-heavy bath bomb into a tub of cold water, the salt crystals will not dissolve as well as they would in hot water. This means that you are going to be sitting on prickly salt crystals, receiving a very unwelcome exfoliation!

Avoid Bath Bombs With Lots of Butters

Butter-heavy bath bombs will not work very well in cold water because heat is required to melt the butters down. The solid fats will clump on the surface of the bath, which is not great to look at or feel, and it also prevents them from being absorbed by your skin. 

How To Adapt Your Bath Bomb For Cold Water

If you love bath bombs, the chances are you have tried your own DIY ones. Perhaps you now only use bath bombs you make at home. However, if you don’t have the faintest idea how to make your own bath bombs, I’ve got you covered with this guide for beginners. You’ll learn how to make a basic bath bomb and also get more advanced recipes to try as you ramp up your skills.

In either case, you can give your normal recipe a bit of an adjustment to make it more cold-friendly. 


Add More Citric Acid To Increase The Fizz

Increase the ratio of citric acid to baking soda to try and increase the fizz. You can play around a bit with this (put on your mad scientist hat!) until you find the perfect cold bath bomb recipe


Reduce The Amount Of Cornstarch To Increase The Fizz

Remember, we said that the purpose of cornstarch in a bath bomb is to slow down the reaction? This is not necessary for a cold-water bath bomb, so you can either reduce the amount of cornstarch you use or remove it from your recipe altogether. 

BONUS: Try This Summer Swim Bath Bomb

Summer swim bath bomb with goggles and sunscreen

If your bath bombs are as precious to you as they are to us, then maybe you don’t want to risk using them in cool or cold water. In that case, why don’t you give this fantastic summer swim bath bomb a try in a warm bath? 

You might not be lying in cold water, but the sight, sound, smell, and overall experience of this bath bomb will feel like you are having a swim down at the beach—is there anything more refreshing than that?

So Will a Bath Bomb Work in Cold Water?

bath tuber

You probably shouldn’t save your favorite bath bombs for a cool summer bath, but instead, play around with your own favorite DIY recipe and see if you can come up with a refreshing version of it for cold water. Just think of all the cool baths you will ‘have’ to take to try out your experimental bombs!

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