Why do I always get sick on holiday?

Airports and train stations are cesspools of viruses.
Mass transit is the likeliest culprit behind vacation sniffles. "You're around more people than usual, in an enclosed space," says Angarone. In airplanes, for example, "the air gets filtered out, but you're sitting with a lot of other people in close proximity, so if the person next to you has a virus and they're sneezing or coughing, that increases your chances of becoming infected." Wondering if the cabin pressure is also messing with your sinuses? Angarone says it might make you temporarily congested, but that sensation generally wears off within a couple hours of landing and it doesn't increase your chances of actually getting sick.