I'm 41, but noticed a change in last 2-3 years.
I also noticed several times that deodorants / anti-perspirants that worked fine for me for 1-2 years, suddenly stopped working at all

The last two years I've been using Mitchum -- heavy duty, but OTC. Works great so far. Unscented, gel clear. Love it, but takes a while to dry prior to dressing.

KNOT: Great info on the baking soda. I may just try it and see if I notice any difference in our hot office. Maybe I'll tell my co-workers about it!