Your St. Bernard's ancestors spent their days climbing the Swiss Alps saving travelers from avalanches, so they have a pretty stoic mindset. Even though your Saint may never come home beaten up from rocks tumbling down a mountain, or sporting a keg of whisky around his neck, he probably gets into his own type of mischief that results in scrapes, scratches, skin irritations, and the like.
Plus, grooming your Saint Bernard involves brushing and more brushing, which can lead to skin irritations, even at the hands of the most experienced groomer. Saints have the skin type that can be prone to hot spots. Watch for any dampness that needs to be dried and attended to, especially during the spring and summer.