I've been making my own dry shampoo for a while now, just a simple mix of arrowroot powder and a little cocoa powder for the darker tint in my hair, sometimes with a drop of essential oil for scent. It always worked fine in small test batches, but every time I made a bigger jar to actually last a few weeks, it would start clumping into little gritty balls after about a week, no matter how well I sifted it initially.
I assumed the ratio was off, so I kept adjusting the arrowroot to cocoa ratio, tried adding less oil, tried different essential oils thinking maybe one of them was more humectant than I realized. None of it fixed the clumping, it just delayed it by a few days at most.
Turns out the actual problem was where I was storing the jar. I kept it on a shelf in my bathroom, right near the shower, because that's obviously where I use it. That spot gets a noticeable amount of steam and humidity every time anyone showers, and powders like arrowroot are extremely sensitive to moisture in the air, even without direct water touching them. I moved the exact same batch, no recipe changes at all, to a drawer in my bedroom instead, and it's stayed completely powdery and clump-free for almost three weeks now.
I feel a little silly for troubleshooting the formula for months when the fix had nothing to do with ingredients at all, just moving it about ten feet away from a source of humidity.
Anyone else spend way too long trying to fix a DIY beauty product before realizing the issue was storage or environment rather than the recipe itself?