Seems like the edges and crevices are more susceptible to tarnish since they may trap moisture...I guess sweat can accelerate it...
Other things that can speed up tarnish (thanks, Google):
"Sterling silver is an alloy composed of 92.5 percent silver and 7.5 percent of another metal, most likely copper. It is the copper in the sterling silver, or silverplate, that causes it to become tarnished"...."The copper reacts to moisture and sulfur in the air, causing the sterling silver tarnish. Silver tarnishes faster in areas with high humidity and air pollution. Chemicals like hairspray, perfume, deodorant, body lotion, bleach, etc., can speed up the tarnishing process."