Coconut oil possesses extremely potent anti-toxin properties such that it'll draw toxins from beneath your skin up to the surface when you apply it topically. This purging of toxins causes acne breakout.
Why do you have toxins beneath your skin in the first place? Thanks to the bad diet and unhealthy lifestyle you're accustomed to. Of course, polluted environment does play a part too. But a poor diet and crappy lifestyle are what trigger acne for city dwellers for the most part.