No one wants the treadmill next to you.
The chemicals in your perspiration can affect the balance and scent of the fragrance, according to scent expert Michael Edwards, author of Fragrances of the World. This is particularly true if you wear natural colognes, since they lack the stabilizing ingredients of many synthetics. Moreover, your diet can alter the smell of your sweat, which mingles with your cologne to create an entirely new, not always pleasing, aroma. Either skip the onions and beer with dinner, or rinse off your cologne before you work out.