Why does my armpit itch so badly?

I was going say it could be a yeast infection , you can get under your armpit .

Why do you buy baking soda and cornstarch from the whole foods store? Do you believe that they are different from the garden variety supermarket kinds?

Let us hope that now, after five years, the OP’s armpit isn’t itching any more.

7 years, you mean! I remember that short time when I was hearing from all sorts of people “in the know” about the evils of aluminum compounds in various products- I see it referenced in this thread a few times. I haven’t heard much about it for half a decade or so, it has been supplanted by general “toxins” these days.