Bath bombs fizz because of a simple chemical reaction: when baking soda (a base) and citric acid meet water, they react and release carbon dioxide gas — the bubbles you see fizzing to the surface. Here's the kid-friendly science.
The two star ingredients
Every bath bomb is built around two powders: baking soda (sodium bicarbonate) and citric acid. While they're dry, nothing happens — they sit together quietly. They need one thing to react: water.
What happens when it hits the water
Drop the bomb in the bath and the water dissolves both powders. The citric acid and baking soda then react, producing carbon dioxide gas. Those rising bubbles are the fizz — the same gas that makes fizzy drinks bubbly.
Where the colour and scent come from
As the bomb dissolves, it releases its colour (swirling through the water) and any fragrance. Skin-softening oils are released too, which is why the water can feel silky afterwards. In our surprise bath bombs, a hidden toy is revealed as the bomb fizzes away.
A fun fact for kids
The fizzing reaction is the same kind you get from mixing baking soda and vinegar in a science experiment — bath bombs just use citric acid instead of vinegar so they smell lovely instead of sour!
Why warm water makes a difference
Reactions generally happen faster in warm water, so a bath bomb often fizzes more energetically in a warm tub than in cold water. Either way, it's completely dissolved within a minute or two.
Frequently asked questions
Why do bath bombs fizz?
Bath bombs fizz because citric acid and baking soda react when they dissolve in water, releasing carbon dioxide gas as bubbles. The reaction stops once the bomb has fully dissolved.
What makes a bath bomb fizz faster?
Warm water speeds up the reaction, so a bath bomb usually fizzes more quickly and energetically in a warm bath than in cold water.
Are bath bombs a safe science experiment for kids?
Yes — the fizzing reaction is gentle and non-toxic, which is why bath bombs are often used as a fun, safe demonstration of an acid-base reaction. Adult supervision is still recommended.