It has been estimated that a whitetail has a nose 3,000 times more sensitive than yours or mine. That's a powerful survival sense! And most other big game have noses just as sharp. Unless you take precautions, deer, elk, bears, and other game animals will smell you from hundreds of yards downwind.
You should always stay downwind from game, but when breezes do not cooperate, you can help your own cause with commercial scent products. Before every hunt, de-scent your lower body with scent-eliminating spray to prevent leaving odor trails to and from your stand, and wear scent-eliminating clothing on stand. During the rut, use quality lures like natural urine to cover your scent and bring animals close.
Some bowhunters do not realize that wind also affects critters' ears. Animals cannot hear well when air currents whistle past their heads and rustle trees and undergrowth. Growing irritated and skittish in the wind, they tuck themselves deep into cover, which makes them difficult to find.
Here's the good news -- you can take advantage of animals by sneaking through heavy cover when breezes blow. If you can find them, you can sneak within bow range of big bucks in cornfields, brush patches, and woodlots, because driving winds reduce animals' ability to hear you coming.