What actually causes most of the trouble
Most of the stomach trouble people pick up in Mexico does not come from the taco stand on the corner but from a duller chain of small lapses: hands not washed before eating, a salsa that has sat four hours in the sun, a plate of fruit cut in the morning and sold in the afternoon. Heat, shifted mealtimes, alcohol and a gut that has never met these particular bacteria do the rest. The stall with a queue and a hot griddle is, statistically speaking, one of the safer places to eat anywhere in the country.
It is worth saying plainly: nobody can promise nothing will happen. Some people eat on the street for three weeks without a twinge and others go down on day two after a hotel breakfast. What you can do is cut the risk with four or five simple criteria, learn to read a stall in ten seconds, and accept that one rough day is part of the trip. Eating well in Mexico happens almost entirely in the street, in a market or in a fonda, and giving that up out of fear means giving up the country itself.
How to read a stall in ten seconds
The first criterion is turnover, and there is nothing mysterious about it: a stall with twenty people around it sells its product in hours rather than days, and the meat cooking right now arrived this morning. An empty stall at the same hour, on the same street, has been holding the same load since yesterday. The second criterion is temperature: anything coming off the griddle, the plancha or the hot oil in front of you passes through a heat point that kills almost everything. What was sitting lukewarm in a tray has been there for an unknown while.
The third is subtler and you learn it by watching: who handles the money and who handles the food. Well-run stalls have two people, or one person who wipes their hands and serves with tongs or a bag. The fourth is the immediate surroundings, meaning whether there is a bucket of cloudy water for rinsing plates or whether the stall works with disposables instead. And the fifth, the most reliable of all, is the hour: eating where the neighbourhood eats, at the time they actually eat, quietly settles almost everything else for you without any further thought.
Fruit, salsas and everything that never sees the fire
Fire solves half the problem, but the other half of the plate arrives raw: the chopped onion, the coriander, the shredded cabbage, the lime wedges, the salsas in their tubs and the cut fruit. None of that goes near the griddle. That does not mean avoiding it, since a taco without any of it is barely a taco, but watching two things: whether the containers are covered or at least in the shade, and whether the stall refills them through the day. A salsa ground fresh in a molcajete and a salsa sitting in the sun since noon are not the same food.
With fruit the rule is simpler still: the less time since it was cut, the better. Carts that peel mango, jícama or watermelon in front of you are an excellent plan and cost roughly $1 – $3 USD (2025); cups assembled at dawn and sitting in a display case, with melted ice pooling underneath, are another matter. Chilli powder, salt and lime disinfect nothing, though the acid helps a little. The same applies to ceviches and seafood cocktails: eat them around midday, somewhere with steady custom, and never at the end of a slow afternoon.
Water, ice and drinks
Tap water is not drunk in Mexico, and Mexicans do not drink it either: virtually every household in the country runs on twenty-litre jugs, and every hotel provides bottles or a dispenser. So far there is no argument. The confusion begins with ice, which attracts a fear that is fairly out of date. The commercial ice used by bars, restaurants and street stalls is made industrially from purified water and arrives in sealed bags; you can usually recognise it because it is cylindrical with a hole through the middle, or in even cubes. That ice is, in practice, as safe as the drink it chills.
Aguas frescas from a busy stall are made with jug water for a practical reason: boiling or filtering on the street is not worth the trouble and a jug costs very little. Even so, anyone who wants to be strict can stick to bottled drinks, beer, soft drinks and anything that arrives hot and sealed. One detail people forget: brushing your teeth with tap water is a minimal risk, while swallowing shower water or water from a badly treated pool is rather less so. A litre-and-a-half bottle costs $1 – $2 USD (2025).
The adjustment days, and when to worry
Almost everyone has two or three odd days early in a long trip through Mexico, and often it is not an infection at all: it is an abrupt change of diet, more chilli than usual, more fat, meals at different hours, altitude in the centre of the country and water with a different mineral makeup. The body complains and then settles. Telling that apart from a real infection is straightforward: mild discomfort without fever clears up on its own within a day or two, while fever, blood, or vomiting that persists beyond twenty-four hours calls for a doctor rather than patience.
One strategy works better than any list of prohibitions: start slowly. For the first two days, eat smaller portions and cooked dishes, drink plenty of water, and do not chain mezcal to raw seafood at eleven at night. From the third day onwards the body is usually ahead of you. Carrying an antidiarrhoeal and rehydration salts from any pharmacy, sold here without prescription for something like $3 – $8 USD (2025), saves hunting for them at three in the morning. Antibiotics are different: do not self-prescribe. Pharmacy consultation rooms are cheap and quick for exactly that.
The mistakes people keep making
The commonest mistake is about timing: turning up at four in the afternoon at a market that has been serving since eight in the morning and ordering whatever is left in the tray. Markets are eaten early and taco stands late; everything has its hour and the neighbourhood knows it. The second mistake is the opposite of the expected one: plenty of people avoid the street entirely and eat three hotel buffet meals a day, which combine lukewarm food, a great deal of handling and hours of exposure. That is a considerably worse model than a hot griddle.
The third is forgetting your own hands. You eat with your fingers, handle cash, grab a metro handrail and then hold a tortilla; a small bottle of hand gel in your pocket solves more problems than any judgement about the stall. The fourth is drinking too much alcohol at altitude and in heat, which produces exactly the symptoms of food poisoning and gets confused with it constantly. And the fifth, sadder than it is serious, is spending the whole trip on international chains out of fear and going home without having tasted anything at all.
What people always ask
Six questions that always come up, answered without the excessive caution of the leaflets or the breeziness of people who have never had a bad night. They run from the everyday to the uncomfortable, and the last is the one almost nobody asks aloud: what exactly to do once it has happened, in a hotel room, at three in the morning, without much Spanish. The short answer is that the pharmacy on the corner, which usually has a small doctor's consulting room attached, handles most cases without any drama at all.
One thing that will not fit in a short answer is worth adding. Mexican street food is, in many cities, the best food in the country and the cheapest: a full dinner of tacos with a drink usually lands between $4 and $9 USD (2025). Stalls that have held the same corner for thirty years did not survive by making their customers ill, because those customers live nearby and come back tomorrow. That, in the end, is the strongest quality control there is, and it explains why the queue test works better than any certificate hung on a wall.