Sweating cools your body from the evaopration of moisture on the surface of the skin. When the air is humid, sweat cannot evaporate from your skin as efficiently as it does in lower humidity because the air has no more room for additional moisture. Hot and humid conditions creat a vicous cycle in which the body is has extreme difficulty cooling. The hotter it gets the more you sweat, but the water cannot evaporate from your skin so you sweat more and more. This might explian longevity issues.
Bacteria on the skin interacting with the glandular secretions in sweat might explain the change you notice in the way a fragrance smells.