The most common types of illnesses are caused by contaminated food and water. If you have problems, mild cases of traveler's diarrhea may respond to Imodium (known generically as loperamide) or Pepto-Bismol. Be sure to drink plenty of fluids; if you can't keep fluids down, seek medical help immediately.
Infectious diseases can be airborne or passed via mosquitoes and ticks and through direct or indirect physical contact with animals or people. Some, including Norwalk-like viruses that affect your digestive tract, can be passed along through contaminated food. Speak with your physician and/or check the CDC or World Health Organization websites for health alerts, particularly if you're pregnant, traveling with children, or have a chronic illness.
Specific Issues in Bermuda
Sunburn and sunstroke are legitimate concerns if you're traveling to Bermuda in summer. On hot, sunny days, wear a hat, a beach cover-up, and lots of sunblock. These are essential for a day on a boat or at the beach. Be sure to take the same kind of precautions on overcast summer days—some of the worst cases of sunburn happen on cloudy afternoons when sunblock seems unnecessary. Drink plenty of water and, above all, limit the amount of time you spend in the sun until you become acclimated.
The Portuguese man-of-war occasionally visits Bermuda's waters, so be alert when swimming, especially in summer or whenever the water is particularly warm. This creature is recognizable by a purple, balloonlike float sack of perhaps 8 inches in diameter, below which dangle 20- to 60-inch tentacles armed with powerful stinging cells. Contact with the stinging cells causes immediate and severe pain. Seek medical attention immediately: a serious sting can send a person into shock. In the meantime—or if getting to a doctor will take a while—treat the affected area liberally with vinegar. Ammonia is also an effective antidote to the sting. Although usually encountered in the water, Portuguese men-of-war may also wash up onshore. If you spot one on the sand, steer clear, as the sting is just as dangerous out of the water.
More recently, divers have encountered the highly poisonous lionfish, which is not a native of the waters. Swimmers will be extremely unlikely to come into contact with one, while divers should just exercise caution around the creatures, which are not aggressive unless provoked.