Bath bombs fizz because of an acid-base reaction: baking soda + citric acid react in water and release CO₂ bubbles. The dry mix stays inert until it hits the bath. The whole skill is adding just enough moisture to bind them without setting off the fizz early.
Ingredients (classic 2:1 ratio)
- 1 cup baking soda
- ½ cup citric acid
- ½ cup cornstarch (slows the fizz, smooths texture)
- ½ cup Epsom salt (fine)
- 2½ tbsp carrier oil (coconut, almond)
- 15–20 drops essential oil
- Witch hazel or water in a spray bottle
- Optional: a little skin-safe mica or natural colorant; dried flower petals
Step-by-step
- Dry mix. Whisk baking soda, citric acid, cornstarch and Epsom salt until no lumps.
- Wet mix. Combine the carrier oil and essential oil (and colorant). Drizzle into the dry mix while whisking constantly so it doesn't clump or fizz.
- Spritz to bind. Spray witch hazel a few pumps at a time, mixing fast, until the mixture just holds together when squeezed — like damp sand. Too wet and it'll activate and puff up; go slow.
- Mold. Pack each half of the mold overfull, press the halves together hard, and unmold immediately by tapping gently.
- Dry. Set on a soft surface and leave 24 hours to harden before handling or storing.
🛁 The #1 fix
If they crumble, they're too dry — add another spritz. If they expand/crack, too wet or too much witch hazel. Humidity matters too; on damp days they take longer to set.
Variations & storage
Lavender calm, citrus wake-up, eucalyptus-mint. Press a few dried petals into the mold first for a pretty top. Store airtight away from moisture; use within a few months (they lose fizz over time).
FAQ
Witch hazel vs water? Witch hazel binds with far less risk of pre-fizzing — worth it. Why cornstarch? It tempers the reaction so the fizz lasts longer. No mold? A metal measuring cup or silicone muffin tin works (flat-bottomed "cupcake" bombs).