Cancún receives millions of visitors per year. That scale means individual choices — where you eat, what products you bring to the beach, who you book tours with — aggregate into something that matters.
Reef safety
The Mesoamerican Reef running along this coast is under real pressure from warming, bleaching events, and chemical runoff. Reef-safe sunscreen (mineral-based, without oxybenzone and octinoxate) makes a genuine difference at the volumes this coastline sees — it's now required at most cenotes and strongly encouraged everywhere near the water. It's also easier to buy before you travel than to find locally.
Where your money goes
Eating at locally-owned restaurants, buying from market vendors rather than resort gift shops, and booking with local tour operators keeps more of your spending inside the local economy rather than routing it to international chains. This isn't a guilt trip — it's just a fact about how resort economies work, and most locally-owned spots are genuinely better anyway.
The environmental picture
Cancún's Hotel Zone was built on barrier-island dune habitat; its coastline is actively managed against erosion in a way that requires constant intervention. Sargassum is partly driven by agricultural runoff nutrients from thousands of kilometers away. These aren't problems individual tourists caused, and individual tourists can't fix them — but knowing the context makes a more honest traveler.
Small things that help
Refuse the plastic bag, carry a reusable water bottle (garrafón water is clean and cheap everywhere), and tip at the local end of the scale — service workers in the tourist economy depend on it more than the menu prices suggest.