Mérida's streets are mild in winter. The day trips bring the bites.

Are there mosquitoes in Mérida? A few in the city in winter, and more on the day trips. Yucatán's 2026 dengue count is low, and the CDC recommends no malaria medicine or yellow fever vaccine for the state. Celestún's mangroves at dawn and dusk, the walk down to the cenotes and the wooded edges of the ruins are where to cover up.

A low dengue year in Yucatán

Mexico's health ministry counted 75 confirmed dengue cases in Yucatán state by October 19, 2026, with no confirmed deaths, against 151 cases and 2 deaths at the same point of 2025. That is 2.95 confirmed cases per 100,000 people, about half the national rate of 5.99, while neighboring Quintana Roo had already passed its 2025 total. The highest 2026 rates are in small towns, led by Ticul, near Uxmal, with 13 cases. The ministry's weekly bulletin recorded no chikungunya, Zika, West Nile or malaria in the state this year through mid-October.

The CDC's malaria areas for Mexico don't include Yucatán, so Mérida, Chichén Itzá, the cenotes, Celestún and Uxmal are all outside them, and the CDC doesn't recommend the yellow fever vaccine for Mexico. Campeche, next door, is a different case. The CDC names the whole state for malaria prevention medicine, and Edzná, Campeche city and Calakmul are all inside it. Celestún's reserve reaches toward Campeche too, so ask a travel clinic if a tour goes deeper than the usual flamingo run. Our Mexico briefing covers the malaria areas and the rest of the country.

Sand flies spread cutaneous leishmaniasis, a skin infection the CDC says is rising in Mexico, and Yucatán counted 33 cases in 2026 through mid-October, against 15 at the same point of 2025. Sand flies bite from dusk to dawn, so a daytime visit to the ruins carries less exposure than a walk on the forest trails at dusk.

Celestún, the cenotes and the ruins

Winter bites in Mérida itself tend to be light. The dengue mosquito breeds in courtyard plants and water containers and bites by day, so a morning coat of repellent over sunscreen still makes sense for the streets.

Celestún, on the Gulf coast about 55 miles (90 km) west of Mérida, draws the strongest warning. Fodor's says mosquitoes gather in great numbers on the beach at dawn and dusk, particularly in winter, the same months the flamingos tend to be most numerous. Book a morning boat tour if you can, wear long sleeves and light trousers, and reapply before the boat enters the mangrove estuary.

The cenotes come with a rule of their own. Yucatán's rules bar tanning lotions, soaps and other products that could harm the water for at least three hours before you go in, and they require a shower first at cenote swimming parks. Bites in the cenotes themselves tend to be few, while the jungle paths and stairs down tend to be buggier. Wear permethrin-treated clothes for the walk in, swim clean and put repellent on after you dry off.

Uxmal and Chichén Itzá are open sites ringed by dry forest. The sunny plazas see few bites, while the shaded edges and trails see more. Keep a long-sleeved layer for late afternoon, when the sand flies begin to bite. The Cancún & Riviera Maya briefing covers the Caribbean side of the peninsula.

Where you're going

Scores are for a December–April trip. December to February is the coolest, driest part of Mérida's year, and the midday heat at the ruins builds from March.

What travelers report

Paraphrased from TripAdvisor forum threads and linked so you can read them in full. Neither is dated, and a wet spell can change the winter picture for a few days.

• Mérida, Uxmal and Progreso · December

  Asking about a December trip to Mérida, Uxmal and Progreso, a visitor was told mosquitoes should be manageable in town, with more at the pyramid sites, and was advised to use repellent on exposed skin along with a hat and sunscreen. TripAdvisor ↗

• Cenotes near Mérida

  In a thread about cenotes and Zika, a poster who dove several cenotes said there were mosquitoes and the three of them got a couple of bites without bug spray, and another noted that cenote operators generally ban sunscreen and sprays to protect the water. TripAdvisor ↗

One rule outlasts the trip. Any fever during the trip or within two weeks of returning means a doctor visit, and so does a bite sore that won't heal. Tell the doctor you were in Yucatán, and in Campeche if you went.

Traveler questions