It's very hard to avoid make-up meltage when it's 100 degrees outside.. but there are some things that you can do if you want to stay fresh.
Switch your foundation to a powder, or a mattifying liquid. ColorScience makes some really great powder foundations, that actually give coverage! If you know my make-up taste, you will understand that it means a lot for me to like powders as foundations, and this is the second I'm reviewing!! I was/am just very turned off by the mineral make-up boom. There was a lot of misuse, a lot of dry looking faces, and just too much hype for me. Now that things have settled, I've gotten over my disbelief, and companies have been constantly improving their formulas, I can come out with my little love for powder : )
Next up is the liquid wonder I've promised. I've seen this product as well, stand up to hours of wear, and heat. Make-up Forever's Mat Velvet+ is the one you've got to get to know. It goes on beautifully, covers wonderfully, and is buildable. I use this on almost all of my brides for looks that last. I use it on myself as well in the summer, and for events when I don't want any breakdown in my make-up. Live it, learn it, love it!! You can check it out at Sephora.
A few other little tips for keeping your make-up, use eyelid primer. Even if you aren't going to wear shadow, it will block the oils from building up on your lids, which can also mess with your liner or mascara. Urban Decay and Too Faced Shadow primers are hands down the best.
Don't be scared to carry a touch up compact with you as well if you aren't into switching foundations.
Happy Summer Lovin!!