It's hardly even worth it to wear makeup in this weather...everything seems to get sweated right off immediately, and even the driest skin gets a little oily when temps climb. If you must put some face on, though. here are some tips to avoid that oil-slick shiny look.
1) Skip cream and liquid formulas...use powder instead.
2) Avoid moisturizer if possible; use an oil-free one with SPF if not.
3) A silicone-based foundation primer will keep makeup in place.
4) Carry extra with you--even with these tricks, you will need to reapply.
5) Oil-blotting sheets are wonder products; you just press them against your skin and they soak up all the oil and sweat without wiping off your makeup like tissue would.
How do you keep makeup on and not shiny in the heat?
I'm really picky about what moisturizer I use on my face & it helps with the oil problem. I can't go without any because I have combination skin & will get flaky, but I use one with SPF 15 in it every day.