If you happen to sweat a lot during the summer especially on your face and neck. The best thing to do to prevent or stop acne is by washing your face. Clean your face twice a day with acne face wash and wipe off in between with witch hazel. If your face is itchy from sweating don't scratch, it will make the bumps or heat rash surface. Lightly moisturize your face and try to stay cool to prevent heat rashes and acne breakouts.
If you perspire a lot apply facial moisturizer to skin, only a little since you might sweat it off. At night rub the normal amount of cream on your face since it should've cooled off by then, that way you don't have to worry about your face being dry and tight.
Important thing to do is to try to stay cool to avoid irritation.