Common sense is the most important factor in avoiding sunburn. Use waterproof and sweatproof sunscreen with a high SPF. Reapply regularly—even the most heavy-duty waterproof sunscreen washes off faster than it claims to on the bottle (or gets rubbed off when you use your towel to dry off). Be extra careful to protect parts of your body that aren’t normally exposed to the sun—a good way to cover every inch is to apply sunscreen before you get dressed—and give your skin a break from direct sun every few hours. Remember that redness from a sunburn takes several hours to appear—that is, you can be sunburned long before you look sunburned.
If you get sunburned, treat it like any other burn by running cool water over it as long and as often as you can. Do not expose your skin to more sun. Reburning the skin can result in painful blisters that can easily become infected. There are a number of products designed to relieve sunburns, most with aloe extracts. Finally, be sure to drink plenty of water to keep your skin hydrated.
The symptoms of heat exhaustion are cool moist skin, profuse sweating, headache, fatigue, and drowsiness. It is associated with dehydration and commonly happens during or after a strenuous day in the sun, such as while visiting ruins. You should get out of the sun, remove any tight or restrictive clothing, and sip a sports drink such as Gatorade. Cool compresses and elevating your legs help, too.
Heat exhaustion is not the same as heat stroke, which is distinguished by a high body temperature, a rapid pulse, and sometimes delirium or even unconsciousness. It is an extremely serious, potentially fatal condition, and victims should be taken to the hospital immediately. In the meantime, wrap the victim in wet sheets, massage the arms and legs to increase circulation, and do not administer large amounts of liquids. Never give liquids if the victim is unconscious.
Diarrhea is not an illness initself, but your body’s attempt to get rid of something bad in a hurry; that something can be any one of a number of strains of bacteria, parasites, or amoebae that are often passed from contaminated water. No fun, it is usually accompanied by cramping, dehydration, fever, and of course, frequent trips to the bathroom.
If you get diarrhea, it should pass in a day or two. Antidiarrheals such as Lomotil and Imodium A-D will plug you up but don’t cure you—use them only if you can’t be near a bathroom. The malaise you feel from diarrhea typically is from dehydration, not the actual infection, so be sure to drink plenty of fluids—a sports drink such as Gatorade is best. You also can take a probiotic like Culturelle, which has Lactobacillus GG, a good bacteria that helps maintain and/or restore the natural balance of your digestive tract. (Pharmacies occasionally carry them, but you’re sure to find probiotics in homeopathic stores.) If it’s especially bad, ask at your hotel for the nearest laboratorio (laboratory or clinic), where the staff can analyze a stool sample for around US$5 and tell you if you have a parasitic infection or a virus. If it’s a common infection, the lab technician will tell you what medicine to take. Be aware that medicines for stomach infection are seriously potent, killing not only the bad stuff but the good stuff as well; they cure you but leave you vulnerable to another infection. Avoid alcohol and spicy foods for several days afterward.
A few tips for avoiding stomach problems include:
Only drink bottled water. Avoid using tap water even for brushing your teeth.
Avoid raw fruits or vegetables that you haven’t disinfected and cut yourself. Lettuce is particularly dangerous since water is easily trapped in the leaves. Also, as tasty as they look, avoid the bags of sliced fruit sold from street carts.
Order your meat dishes well done, even if it’s an upscale restaurant. If you’ve been to a market, you’ll see that meat is handled very differently here.
Insects are not of particular concern in the Yucatán, certainly not as they are in other parts of the tropics. Mosquitoes are common but are not known to carry malaria. Dengue fever, also transmitted by mosquitoes, is somewhat more common but still rare. Some remote beaches, like Isla Holbox and the Costa Maya, may have sand flies or horseflies, but they have been all but eliminated in the more touristed areas. Certain destinations are more likely to be buggy, like forested archaeological zones and coastal bird-watching areas, and travelers definitely should bring and use insect repellent there, if only for extra comfort.
The Yucatán Peninsula  is generally quite safe, and few travelers report problems with crime of any kind. Cancún is the one area where particular care should be taken, however. You may find illicit drugs relatively easy to obtain, but bear in mind that drug crimes are prosecuted vigorously in Mexico (especially ones involving foreigners), and your country’s embassy can do very little to help. Sexual assault and rape have been reported by women at nightclubs, sometimes after having been slipped a “date rape” drug. While the clubs are raucous and sexually charged by definition, women should be especially alert to the people around them and wary of accepting drinks from strangers. In all areas, common-sense precautions are always recommended, such as taking a taxi at night instead of walking (especially if you’ve been drinking) and avoiding flashing your money and valuables, or leaving them unattended on the beach or elsewhere. Utilize the safety deposit box in your hotel room, if one is available; if you rent a car, get one with a trunk so your bags will not be visible through the window.