French fries can cause acne breakouts if they are salty. There is no direct proof that eating french fries or other “greasy” foods increases the severity of acne. Nevertheless, there is proof that both salt and hyperglycemic food (carbohydrates) may increase number of acne breakouts.
Another thing: eating french fries of other “greasy” foods may leave oil debris around your mouth. If these debris are not washed they may by themselves cause acne breakouts in this area.
Your MDacne app has some nice video tutorials on the types of foods to avoid when you have acne.