It's funny how researchers can do specialized studies to "prove" something - when really in real world terms they have not proved anything at all. Some researches feel they have proven that greasy food never causes acne. Here's the issue.

I have an acne problem, and I'm in my 30s, so I'm not a teenager. I've had many years to experiment with various situations and to see how my skin reacts. We also tend to eat a fair number of McDonalds meals in our car :) Now, let's say we drive up to a McDonalds and place our order. My skin feels fine, normal. We get our order and drive away.

As that bag of french fries, hot and oily, sits in the car, the oil starts to float around in the atmosphere. That's how you smell it of course - your nose is interacting with little particles of oil that are floating in the air. I don't eat the french fries, but even without eating them, my face starts to get oily. After about 5-10 minutes, I can run my finger across my forehead and feel the oil there. It's not because I ate anything, because this happens without me eating a bite. It's from the oil from the food, filling up the car.

Of course, you could say this oil didn't cause any acne. It's just oil. But if just some of that oil gets dried out over a pore, then it is now blocking the pore, and causing an oil bubble to form, which will get infected and be acne. If you are already fighting an acne problem, it can really make a huge difference to keep your environment as oil-free as you can.