Zinc earns a bullet point on half the natural deodorants on the shelf and an explanation on almost none of them. That's a shame, because how zinc stops body odor is the entire reason BioShield™ is built around it, and it's a lot more interesting than “now with zinc.”
Body odor is a chemical reaction. Zinc interferes with that reaction, grounding the smelly molecules and slowing the bacteria that make them, instead of masking the result or blocking your sweat.
The short version
Body odor is a chemical event: bacteria on your skin break down compounds in your sweat and produce smaller, smelly molecules. Zinc interferes with that event. Rather than covering the result (fragrance) or removing the moisture (aluminum), zinc acts on the process that creates odor in the first place. That's what “eliminates odor at the source” means in chemical terms.
A little deeper
Zinc works on more than one front, which is the point of using it.
Zinc ions bind to some of the malodorous molecules bacteria produce, particularly thiols and short-chain fatty acids, and convert them into larger, non-volatile compounds. A molecule that can't become airborne can't reach your nose.
Upstream, zinc influences the bacterial and enzymatic activity that generates those molecules to begin with. Less of the odor-producing process runs, so there's less to deal with downstream.
Why a system beats a single active
Zinc alone is good. Zinc as part of an engineered system is better, because odor isn't a single reaction, it's a chain of them. BioShield™ pairs zinc with supporting ingredients that address different points in that chain, so the formula has depth instead of one mechanism doing all the work. When conditions get harder, heat, a long day, heavy movement, depth is what keeps performance steady.
This is also why the BioShield formulas share the same zinc core but aren't identical. Core and Max pair the zinc with magnesium, which neutralizes acidic odor compounds as they form. Sensitive skips magnesium and instead works with your skin's own chemistry, which is why it suits reactive skin and is Dermatologist Tested. There's a fuller breakdown in neutralize vs. interrupt.
See it all together on the BioShield page, or find your formula in the buyer's guide.