Different environments can make your skin oilier or even mess up your makeup; things like air conditioning or forced air heating wreak havoc on skin and makeup. There are great little oil blotting powder papers that can take the shine off in a jiffy and lay down enough powder that you don't have to think about it. They come in little packages that fit easily into a purse. Of course, you can always freshen up with a powder compact, providing it has a decent mirror and the light you're repairing your makeup in matches the light where you spend your time. Never try to fix your makeup in a dingy restroom and hope it'll look all right in the fluorescent light of the office or classroom. Better to hide under your desk for a quick pat of powder.