If you've ever flipped over a bath bomb and read the ingredient list, there's a good chance you've seen cornstarch near the top. It's one of the most common ingredients in commercial and handmade bath bombs alike. So why don't we use it at Aquinas Soap Company?
It's a question we get asked sometimes, and we think it deserves a real, honest answer.
Why Most Bath Bombs Contain Cornstarch
Cornstarch is popular in bath bomb recipes for a few reasons:
- It slows the fizz. Cornstarch acts as a buffer between the baking soda and citric acid, slowing down the reaction so the bath bomb doesn't fizz too fast when it hits the water.
- It adds bulk. It's an inexpensive way to increase the size and weight of a bath bomb without adding significant cost.
- It creates a silky feeling. Cornstarch can give bathwater a slightly silky texture.
On the surface, these seem like reasonable benefits. So what's the problem?
The Issue with Cornstarch in the Bath
The concern with cornstarch isn't that it's toxic — it's not. The issue is what it can do in a warm, wet environment.
Cornstarch feeds yeast. Yeast, including Candida (the organism responsible for yeast infections), thrives on starch. A warm bath is already an environment where yeast can flourish — adding a starch-based ingredient to that environment is something many women's health practitioners advise against, particularly for anyone who is prone to yeast infections or vaginal irritation.
While the research on bath products and yeast infections is nuanced, and not everyone will be affected, we believe in a simple principle: if there's a reason to leave something out, and there's no meaningful sacrifice in quality, we leave it out.
What We Use Instead
Removing cornstarch from a bath bomb formula means rethinking how to control the fizz and create a luxurious experience without it. Here's what we rely on instead:
- Careful ratios of baking soda and citric acid — getting the balance right means the fizz is controlled naturally, without needing a buffer.
- Nourishing oils and butters — ingredients like coconut oil, shea butter, and cocoa butter deliver the silky, moisturizing bath experience that cornstarch only mimics.
- Kaolin clay — in some of our formulas, we use a small amount of kaolin clay, which is gentle, skin-loving, and adds a luxurious softness to the water without the yeast concerns.
Our Philosophy: Every Ingredient Earns Its Place
At Aquinas Soap Company, we don't add ingredients just because they're conventional or because they make production easier. Every ingredient in our bath bombs is there because it genuinely benefits your skin or your experience — full stop.
Cornstarch doesn't meet that bar for us. It's a filler, and we'd rather fill our bath bombs with things that actually do something good for you.
That's the Aquinas Soap Company difference: small-batch, intentional formulation, with nothing added that doesn't belong.
Ready to try a bath bomb made without compromise? Shop our full bath bomb collection — each one handcrafted with your skin in mind.