Majacat's avatar profile says Copenhagen, so it is celsius.
I spend a good amount of time in Palm Springs, CA where it is currently 105 farenheit. It gets brutal in the summer. The heat will melt emolient products (i.e. lipsticks, CCBs, etc) if they are in direct sun or in extreme heat for a long period of time. Warm temperatures can cause your emollient products to sweat as well.
Chances are though, you are staying in a climate controlled environment, i.e. house or hotel with air conditioning, so it won't be a problem.
I would just try to keep them as cool as possible during the trip. If they do get soft, give them about an hour or so to set or firm up in a cooled environment before you use them again.
I always carry my makeup in my carry-on luggage. That way it is always in the relatively cool environment of the plane cabin.
If you don't have room in your carry-on, or safety restrictions won't allow you to carry it on, you could pack your makeup in a soft-sided lunch bag with a freezable ice packet (like the ones you put on an injury. The ones full of that mystery blue goo). Then put that in your luggage. That would keep everything cool for the trip. I would also put the freezable ice packet and makeup in ziploc bags, as everything has potential to expand and pop open. That gooey blue stuff in the freezble ice packets would be a mess if it got all over your makeup.
The heat won't ruin them. If they melt and refirm, sure...I guess it takes somewhat of a toll on their life span, but I wouldn't worry. Prolonged, direct exposure to extreme heat and humidity is more of a problem.
Just remember that there are plenty of gals from Southern CA to Qatar who buy and use MAC. It works for them.
Where are you going, BTW? Regardless, enjoy your trip!