I am convinced that the reason we all seem to break out the most in the winter months is because during the summer months, we sweat a lot, releasing lots of bad toxins from our body. In fact, that's what sweat is--the body's release of bad toxins. (okay that sounded kinda repetitious, but you get it...)
During the winter, we stay inside a lot and it's colder, so we rarely sweat. And since our toxins aren't able to be released through the normal means of sweating, they build up inside. And after a while, they have to leave the body somehow, so they come out in the form of acne.
I think the lack of sunlight also has an affect on the acne as well.
As a solution, we should probably find ways to get the bad toxins out through sweating. For example, maybe we should go jogging and drinking more water.
I live in Minnesota and just about anyone that can afford it has their own personal sauna. Obviously, its cold as hell here, and Minnesotans understand the importance of toxin release, so they use the saunas daily to force their bodies to sweat out the toxins that otherwise would never be released in this cold-as-hell place.
So hopefully this helps.