How to make bath bombs with citric acid

The fizz in a bath bomb comes from two simple powders: citric acid and baking soda. Here is an easy beginner recipe you can make in your kitchen.

How the fizz works

Citric acid and baking soda don’t react while they are dry. When they hit the bath water, they react and release carbon dioxide bubbles. That is the fizz.

What you need

• 1 cup baking soda
• ½ cup citric acid
• ½ cup cornstarch
• 2½ tablespoons oil (coconut, almond or olive)
• 1 to 2 teaspoons water, in a small spray bottle
• Optional: a few drops of skin-safe fragrance or essential oil, and skin-safe colorant
• A bath bomb mold, silicone mold or muffin tin
• Gloves

Step by step

1. Whisk the baking soda, citric acid and cornstarch together in a large bowl until there are no lumps.
2. In a small cup, mix the oil with any fragrance or color you are using.
3. Slowly drizzle the oil into the dry mix while whisking.
4. Spritz with water one or two sprays at a time, mixing as you go. Stop when the mix holds together like damp sand when you squeeze it. Too much water will start the fizz early.
5. Pack the mix firmly into your mold and press it tight.
6. Let it dry for at least 24 hours in a dry spot, then gently pop it out.

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Tips for better bath bombs

• Crumbling? The mix was too dry. Add another spritz or two of water next time and pack the mold harder.
• Puffing up or cracking? Too much moisture. Make them on a dry day and add water more slowly.
• Storage: keep finished bath bombs in an airtight container so humidity doesn’t set them off.