By some metrics, gastrointestinal infections related to food or water affect 30 to 70 percent of all travelers during or immediately after their trips, according to a 2015 study in BMJ Clinical Evidence. Each year, one in six Americans and nearly one in 10 people worldwide suffer from such illnesses caused by bacteria (E. coli, salmonella, listeria), viruses (norovirus, hepatitis A), or parasites (giardiasis, roundworms, tapeworms).

Lower-income countries have a reputation for putting travelers at a higher risk for food poisoning, but people are just as likely to be sickened from an improperly handled meal in Italy or Australia—or from some sushi at their local supermarket.

Here’s why people get food poisoning, what to do if it strikes, and how to (maybe) prevent it.

What causes food poisoning?

There are 31 major known pathogens that cause foodborne illnesses, including norovirus, salmonella, E. coli, clostridium perfringens, and campylobacter. Depending on the bacteria, parasite, or virus, symptoms could include a few hours to a week of diarrhea and vomiting, plus stomach cramps, fever, or body aches. The most likely culprits? Raw or undercooked chicken, turkey, or meat; raw milk; raw fruits and vegetables; shellfish; and food stored in unsafe temperatures (e.g. an open-air buffet) or prepared in an unsanitary way.

Or the water might be making you sick. According to the U.S. Centers for Disease Control (CDC), more than 180 countries (including popular destinations the Maldives, Mexico, and the Bahamas), have tap water that is unsafe to drink. This means that brushing your teeth with local tap water or even washing your hands before preparing lunch could lead to illness.

“Giardia parasite is pretty common with contaminated water,” says Cindy Chung, a doctor at Kaiser San Rafael Pediatrics in California. “When a kid comes into my office with sudden diarrhea, I ask, ‘Have you been camping? Did you go to the beach? Have you traveled?’”

What can I do if I get sick?

There’s no quick fix for foodborne illnesses. Most will resolve once the bacteria or toxins have been flushed out through watery diarrhea or vomiting. To combat the discomfort during this unpleasant period, doctors recommend ample fluids to prevent dehydration and over-the-counter painkillers (ibuprofen, naproxen) for stomach cramps.

Since diarrhea and vomiting are your body’s natural immune response to expel toxins, only take anti-diarrhea and anti-nausea medications such as loperamide (Imodium A-D) and bismuth subsalicylate (Pepto-Bismol) if you’re boarding a bus or airplane and won’t have easy bathroom access.

To stay hydrated, Chung recommends Pedialyte or low-sugar Gatorade. “Too much sugar makes you feel worse when you have vomiting and diarrhea,” she says. For severe cases, especially for children or the elderly, consider having a doctor prescribe ondansetron (Zofran), a medicine that slows down vomiting so you can drink more fluids.

You may be able to cancel or reschedule travel if you’re too ill to move. Travel insurance sometimes considers food poisoning a valid reason to make flight changes. “But you can’t go to the doctor the day after your missed flight and get a retroactive diagnosis,” says Michelle Couch-Friedman, an ombudsman columnist for The Points Guy and founder of Consumer Rescue, a consumer advocacy organization.

What to do before a trip

Worried about getting sick on a trip? Consult your general practitioner or a travel clinic for recommendations on medications or vaccinations based on your destination. “We might give you a three-day course of azithromycin (Zithromax) because, with traveling, one of the most common bacteria is E. coli,” says Chung. “But we tell patients not to use it unless their stools have blood.” A doctor may give you a hepatitis A vaccine to prevent illness from contaminated food or water.

To help ward off diarrhea, experts at Mount Sinai recommend taking two Pepto-Bismol tablets, four times a day, before and during your trip. This advice is based on a landmark 1987 study of students traveling to Mexico, which showed that Pepto’s active ingredient, bismuth subsalicylate, reduced the incidence of traveler’s diarrhea by approximately 60 percent.

“Generally, E. coli is the most common cause for traveler’s diarrhea, and the medication may help prevent the bacteria from taking hold and [you] developing any symptoms,” says Michael Bolaris, chair of pediatrics and chief of infectious disease at Rancho Los Amigos National Rehabilitation Center in Downey, California. Bolaris cautions that taking bismuth subsalicylate might temporarily give travelers harmless black stools or tongues.

Pack electrolyte powders, water purification tablets, filtered water bottles, and hand sanitizer as well as anti-diarrhea, anti-nausea, and anti-inflammatory medications. Keep supplies in your carry-on, in case of mid-flight sickness or lost luggage.

Remember that the water in airplane bathrooms isn’t potable. “You may actually be introducing yucky microbes by washing your hands prior to a meal or brushing your teeth,” says Couch-Friedman. “Bring a bottle of spring water into the bathroom to brush your teeth, and use hand sanitizer. Otherwise, you could fast-track yourself to gastrointestinal problems.”

What to do during a trip

Find out if the tap water is safe to drink in your destination with the CDC’s Traveler’s Health tool. Many hotels in places with unsafe water have their own filtration systems or provide bottled water. But nasties may come from that iced water at a street market or berries at a roadside food stand. When in doubt, avoid ice, and drink bottled water.

Concerned about single-use plastics? Bring a heavy-duty filtered water bottle (such as Grayl) and fill it with boiled water (if the hotel has a kettle) or water treated with purification tablets (Globaline, Potable-Aqua).

Sometimes, food poisoning happens because travelers have never encountered common bacteria and viruses at their destination. “Locals build up some level of tolerance because their immune systems have been exposed multiple times,” says Bolaris.

That doesn’t mean you have to forgo street food in Southeast Asia or taco stands in Mexico City. Bolaris’ rule? If you can’t clean it or peel it, don’t eat it. Chung advises travelers to watch how vendors prep food. “Are they using utensils, gloves, or bare hands?” When in doubt, stick to piping hot dishes—grilled meats or fried fritters—and shun raw seafood and lukewarm stews.

Help might be coming

A few companies are developing a vaccine against norovirus, which infects 700 million people a year worldwide. The U.S. Food and Drug Administration is launching new Food Traceability Rules in 2026, designed to reduce foodborne illness and deaths by making it easier to trace contaminated foods—cheeses, fruits, vegetables, and seafood—throughout the supply chain.