Oil can come from surprising places.  While your skin produces extra oil to make up for oil deficiencies if you don’t eat enough good fats, it obviously produces a lot of oil if you eat too many bad fats. 

But in addition to that, you can actually find oils that may clog your pores not only in your make up, but also in your sunscreen.  So while it’s good to protect your face from the sun in the summer, you have to be very sure to get sunscreen that doesn’t have those extra oils, which can be harder than many would expect, or it will clog your pores. 

Third, you could actually get oil from your hair.  Your hair naturally has its own oils.  But when you have bangs or other hair that hangs over your face, you actually don’t produce more oil so much as the oil get stuck on those bangs and then goes back onto the face, back and forth keeping oils in that area. 

Finally, you want to watch out for your phone.  Your phone can cause acne yes.  As you use it, especially in hotter conditions, you naturally may sweat, in part because your phone gets hotter with use in general terms.  This will cause your face and oils to sweat and produce oils visibly getting on your phone, but also getting back on your face and causing greater acne breakouts.