Mosquitoes suck

Mosquitoes rule the land here, especially at dusk and when the wind isn't blowing. Bring mosquito repellent with DEET from home, since it is hard to come by. Be advised that although DEET is the best stuff when it comes to keeping the bugs away, it is a potent chemical and care should be used when putting any repellent containing DEET on children.

If you are traveling with children, make sure the repellent you purchase contains no more than 10% DEET and that you read all directions and warnings before use. Sleep in screened rooms or under mosquito netting and before you fall asleep kill any mosquitoes that snuck inside. Mosquito coils are for sale everywhere and work like incense to keep the bugs away for 6 hours.

Although uncommon, there are mosquito borne illnesses around, like dengue fever and malaria. They aren't common, and visitors usually don't need to take antimalarial medicines. Most symptoms take several days to present themselves, and you will most likely be home by then. If you get symptoms - fever, severe headache, muscle and joint pain, nausea and vomiting, jaundice or abdominal pains - go to the doctor and tell him/her that you were in Mexico and got bitten by mosquitoes.

Don't touch that stray dog

There are stray dogs and cats all over. You can trust that none of them have had their rabies shots. Any bite, scratch or even lick from a warm-blooded, furry animal should be immediately scrubbed with soap and water and cleaned with alcohol. If there is a possibility that the animal is sick, seek medical treatment.

Jellyfish sting

There aren't a lot of jellyfish around. Most of the stings that do occur come from Agua Mala ("bad water"), also called sea lice, which are baby jellyfish - or maybe something else, nobody is sure. You can't see Agua Mala, but if you feel sharp stinging while you are swimming, go into shore. Immediately wash the affected area with vinegar. Let the vinegar dry, then shower and reapply the vinegar. Treatment is the same for jellyfish stings. If the sting starts itching, cover it with Calamine lotion. Agua Mala itches like crazy.

Don't poke the fish

Most of the area's fish, even the nurse sharks, are not dangerous, unless you bother them by chasing, cornering or poking them. There is a guy here who had his finger bit down to the first knuckle. He was trying to get a little puffer fish to inflate by messing with it. That fish had a tasty finger snack.

When on the reef, absolutely don't touch or stand on the coral. It looks like rock, but is a living creature which is killed by touch. Coral grows so slowly, that breaking off a tiny piece could undo 10 years of growth. Instead, look for pieces of dead coral on the beach. Also, some of it is fire coral which will give you a nasty itch rash - but don't look for sympathy, you shouldn't have been touching the coral anyway.

Frommer's Cancun, Cozumel and theYucatan Completely updated every year by the experts.