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The Science Behind Bath Bombs

Stephanie Tuba

Posted on February 25 2019

The Science Behind Bath Bombs

By: Sawyer Cecena

If you’re a bath enthusiast like me, then you know that the only thing better than a nice, hot soak in the tub is adding in a bath bomb. Whether you prefer the ones with cool colors or super sweet scents, there’s a bath bomb out there for everyone. In fact, since inventor and Lush co-founder Mo Constantine came up with the idea for bath bombs in the late 1980s, the product has become extremely popular across the world – with over 20 million sold in the year 2017 alone!  But, beyond being a super cool addition to your bath time routine, these fizzy treats have an awesome science behind them. If you’ve ever wondered just how your bath bombs work their magic, keep reading to find out!

A Love Affair

While every bath bomb is unique, most start out with the combination of citric acid and baking soda. When you drop the product into the tub, the baking soda and the citric acid begin to liquify. While the two components of baking soda, sodium and bicarbonate have a breakup, a hydrogen ion from the citric acid also gets away from the rest of the molecule. Then, that hydrogen ion from the citric acid and the bicarbonate from the baking soda get together and produce carbon dioxide. Since carbon dioxide is a gas, this is what creates that fizzy, bubbly reaction once the bath bomb hits the water.

Slow Your Roll

Another key ingredient to bath bombs is cornstarch, which actually plays the most important part in keeping those interactions between the citric acid and the cornstarch under control. The cornstarch sticks to the other ingredients and forces them to slow down the rate at which they dissolve. Otherwise, that fizzy reaction would only last a few seconds as opposed to the full few minutes we are used to. Thanks, cornstarch!

But What About the Fun Stuff?

Of course, the best part of a bath bomb is aesthetic. Some draw you in with cool colors and shapes, while others have some extra special additions like scents or little prizes hidden inside. Once that basic mixture is put together, that’s when the fun stuff begins. Shapes like roses or cupcakes are made by scooping the mixture into a mold and leaving it in overnight to form to the shape. The colors typically come from the same FDA approved colorants that are used in cosmetics. Essential oils like lavender or amber are what give your bombs their awesome scent.

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