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What causes bath bombs to fizz? © Shutterstock

What causes bath bombs to fizz?

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It's chemistry, but in this case let's call it fizz-ics.

Asked by: Lauren Kathleen Mahaney, Tennessee


Bath bombs fizz when water triggers a reaction between an acid and a neutralising substance known as a ‘base’. Many bath bombs contain citric acid, as found in citrus fruits, and sodium bicarbonate, which is a weak base. The dry chemicals are stable, but in water they react together to produce carbon dioxide bubbles (fizz) and, as a by-product, sodium citrate salt. The reaction helps to break up the bath bomb, releasing fragrances, detergents and oils.

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Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.


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