Why is food poisoning so common in Mexico?

All the countries that I’ve travelled to came with health warnings. For Thailand, for example, I was warned not to drink anything that had ice cubes in it, as, while the drink itself would probably be fine, the ice cubes would likely be from unsafe tap water. Ultimately, I found iced drinks too hard to avoid, but there were no consequences. Mexico, however, was the only country where I was assured that I would almost definitely get food poisoning. Mexican food poisoning is notorious to the point that it has its own nickname: Montezuma’s Revenge. The name “Montezuma” is the English version of “Moctezuma”, which itself is the Spanish corruption of Motecuzomah, the Aztec huey tlatoani (literally “great speaker” – the title for their king or emperor) who was usurped by the conquistadors. I am not a conquistador, but his revenge was still swift and brutal, which seems unfair.

I’ve been to a number of countries that are on a similar level of development to Mexico, and none of them had food that did this to me. It wasn’t the spice level – contrary to what you might think, Mexican cuisine isn’t usually spicy, it’s just that there are generally little pots of salsa on the table with each meal. Thai cuisine is far spicier, and that didn’t give me days of stomach cramps.

So, it’s not Mexican chillies that wreak such havoc on the soft, vulnerable bowels of foreigners. Mexican cuisine does feature some unfamiliar ingredients (the caldo tlatlpeño soup I had in Mexico City contained something that was translated into English as “wormwood”), but they all seem benign enough. There’s no reason to suppose that Mexican food hygiene is any worse than those of other countries on a similar income level. But, when compared to other countries that are also classified as being “middle-income”, without such a reputation for food poisoning that it has a specific national nickname, and, crucially, did not inflict such suffering on me when I went there, a specific statistic from the World Health Organisation in 2022 does stand out:

It’s not the food after all – it’s the water. I had retrospectively viewed the tamale I had in Mérida with such suspicion, but all the while it was more likely that strange drink made with an unfamiliar herb that I had.

According to data from the World Bank, Mexico has seen a huge increase in population in the last 20 years, similar to the other three countries (and the rest of the world), but a more sustained increase in agriculture, and a far more pronounced increase in manufacturing. Its water infrastructure has failed to keep up, resulting in a huge amount of pollution in its water sources, from chemicals used in industry and agriculture to poorly-treated sewage. According to National Water Commission of Mexico, 54% of what is termed “wastewater” is not treated, and instead used to irrigate farmland or dumped into water bodies. Even when treated, water can be contaminated in the plumbing system by corroded pipes or during maintenance work.

Mexicans themselves are fully aware of this, and generally avoid drinking tap water, but they still can’t avoid it completely. A study in Gudalajara in 2018 discovered that although only 7% of households would drink the tap water, 95% use it to wash fruit and vegetables. Furthermore, a very recent study in July in Culiacan this year found that even 34% of bottled water contains an unsafe level of pathogens. The same study found indications of “faecal contamination” in 29% of household water samples. TravelHealthPro (the website for the National Travel Health Network and Centre) notes that diseases such as traveller’s diarrhoea and cyclospora (most British cases of the latter in the past year originated in Mexico) are caused by food and drink that have been contaminated by human faeces.

Despite the dramatic nickname, rooted in conquest and colonisation, the origins of Montezuma’s Revenge is ultimately as earthy and disgusting as its effects.

Sources: The Rough Guide to Mexico (2025) / The Broken Spears: The Aztec Account of the Conquest of Mexico by Miguel León-Portilla / World Health Organisation / World Bank / Occurrence of emerging organic contaminants and endocrine disruptors in different water compartments in Mexico – A review by Ivón Vázquez-Tapia et al, 2022, Chemosphere (Volume 308, article 136285) / Assessment of thermotolerant coliforms, Escherichia coli, and Pseudomonas aeruginosa throughout a drinking water treatment plant and supply system in Culiacan, Mexico by Cecilia Sánchez-Armenta et al, 2026, Scientific Reports / TravelHealthPro