[user104658]

Given that other factors haven't changed much in recent years (smoking actually on the decline in younger generations)... I can only imagine that the major causes are pollutants and processed foods? Maybe even microwaving, given how many people just ignore the fact that you're supposed to leave food to stand for a minute after cooking in a microwave.

I can't see it being down to oral sex or alcohol, people have been doing those for thousands of years .