why did recently over the past month my left armpit started smelling bitter and foul?

More information: 
my right armpit smells completely normal, but my left almost smells like mold. it smells very bitter and moldy. I have tried switching from my natural deoderant back to old spice which I used to use and have zero problems and it went away from a little bit. Recently came back stronger then ever.


Hi Robert, over time the underarm microbiome can change. Such a change can cause a different underarm odor. Deodorants are not really changing the microbiome, so that's why the odour is persistent. We're working on it though. Best, Chris