Health hazards range from mild headaches to run-ins with wild animals, but the latter happens less frequently than car accidents in the parks. To be safe, you might want to keep a first-aid kit in your car or luggage, and have it handy when hiking. It should include at least butterfly bandages, sterile gauze pads, adhesive tape, an antibiotic ointment, pain relievers for children and for adults, alcohol pads, a pocket knife with scissors, and tweezers. Healthcare is available at clinics in both parks; hospitals with 24-hour emergency rooms are located in Jackson and Cody, Wyoming, as well as in Bozeman, Montana.

Altitude Sickness -- Because most of us live at or near sea level, the most common health hazard in the parks is discomfort caused by altitude sickness. Adjusting to the parks' high elevations is a process that can take a day or more. Symptoms of alcohol sickness include headache, fatigue, nausea, loss of appetite, muscle pain, and lightheadedness. Doctors recommend that, until acclimated, travelers should avoid heavy exertion, consume light meals, and drink lots of liquids but little caffeine or alcohol.

Bugs, Bites & Other Wildlife Concerns -- Wildlife are to be treated with utmost respect in both parks. Keep your distance -- at least 300 feet if possible -- from any wild animal in either park. Mosquitoes, spiders, and ticks are the most bothersome biters, aside from the occasional rattlesnake you might see around Gardiner, Montana.

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The roads are the most dangerous places in Yellowstone, so be especially cautious while driving. Lightning and falls are also killers, but wildlife is the most unique peril in the parks. The most dangerous animal in either park might well be the grizzly bear, but all wildlife has the potential to injure a human. Keep a safe distance from buffalo, deer, moose, and other animals -- at least 300 feet. Most people have a healthy respect for bears and are content to view them from a distance. But because a close encounter can happen unexpectedly, you need to know what to do in this situation. First, be aware that what matters most to a bear are food and cubs. If you get between a sow and her cubs, you could be in trouble. If a bear thinks that the food in your backpack is his, you also have a problem.

Unless bears have already developed a taste for human food, though, they won't come looking for you. Make a lot of noise on the trail through bear habitat, and Ursus arctos horribilis will give you a wide berth. Don't camp anywhere near the carcass of a dead animal; grizzlies sometimes partially bury carrion and return to it. Hang your food bag high in a tree, keep your cooking area distant from your campsite, and don't keep any food or utensils in your tent -- or even clothes worn while cooking. Soaps and other perfumed items can also be attractants.

Avoid hiking at night or in the meadows of mountain areas if visibility is poor. Bears have an extremely good sense of smell but poor eyesight.

If you encounter a bear, here are some things you should and should not do:

  • Do not run. Anything that flees looks like prey to a bear, and it might attack. Bears can run at more than 30 mph. The bear might bluff charge, but you're best off holding your ground.
  • Avoid direct eye contact.
  • If the bear is unaware of you, stay downwind (so that it doesn't catch your scent) and detour away from it slowly.
  • If the bear is aware of you but has not acted aggressively, slowly back away.
  • Do not climb a tree. Although black bears have more suitable claws for climbing, grizzly bears can climb trees, too.
  • Make noise and act intimidating if the bear does not retreat.
  • If you're attacked, drop to the ground face down, clasp your hands over the back of your neck, tuck your knees to your chest, and play dead. Keep your backpack on -- it can help protect your body. Only as a last resort should you attempt to resist an attack and fight off a bear.
  • If you carry pepper spray, be sure that it's handy when you're in possible bear habitat, not buried in a backpack. If you use it, aim for the bear's face and eyes. After you use it, leave the area: Bears have been seen returning to sniff about an area where spray has been used.

Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.