Apply 2-3 sprays of unscented magnesium oil directly to clean underarms. Allow it to dry for a moment before getting dressed.
If you find the magnesium oil itchy or drying, consider applying a natural moisturizer or oil, like jojoba oil, afterward.
Notes
As with any new skincare product, do a patch test to make sure you don't react to the product. Some tingling is normal at first, but if irritation persists , discontinue use.
It's best to use an unscented and pure magnesium oil that doesn't contain any added ingredients or fragrances (like this one).
If you'd like to make your own magnesium oil instead of buying a premade one, you can dissolve equal parts of magnesium chloride flakes into water and add to a clean spray bottle.