The conversation about street food safety tends to arrive in one of two forms. Either everything sold outdoors is dangerous, or the worry is neurotic and anybody who gets ill is weak.
Neither has been my experience. I have eaten street food regularly for twenty years and been ill from it perhaps four times, and the four times had things in common.
This is observation rather than public health advice, and anyone with a specific medical vulnerability should get proper guidance rather than mine.
Heat is the single biggest factor
The pattern in my own experience is that trouble came from things that were not hot when I ate them.
Anything that comes straight off a hot surface, at a temperature that makes you wait before biting, has been through a process that deals with most of what would make you ill.
Anything cooked earlier and sitting at room temperature is a different proposition, and the longer it has been sitting the more that matters.
This is why the busiest stalls tend to be safest, which sounds like folklore and has a mechanical explanation. High turnover means nothing sits. A quiet stall selling the same food may have had it standing for hours.
The water question, which is the real one
Most of the specific incidents I can trace were not the cooked food. They were what came alongside it.
Water, obviously. Ice, which people forget is water. Chutneys thinned with water and kept at ambient temperature. Salads and garnishes washed in whatever was available. Cut fruit.
The cooked item on the plate had been through high heat. The cold accompaniments had not.
This also explains why visitors get ill more than residents at the same stall, since the relevant difference is exposure to local water rather than to local food.
What I look at before eating somewhere
Not cleanliness in the general sense, which is a poor guide. A cart can look rough and be fine.
What I actually look at: whether the cooking surface is genuinely hot; whether there is a queue and things are moving; whether raw and cooked items are handled with any separation; and what the water situation looks like — is there a covered container, is ice being handled with bare hands, is a cloth being reused for everything.
The cloth is a surprisingly good indicator. A vendor with a clean cloth changed regularly is thinking about it. One wiping everything with the same grey rag is not.
And how the money is handled relative to the food, which in the best places is a separate person or at least a deliberate separation.
The adaptation argument
People who live somewhere do get ill less often from local food, and it is worth being clear about what that does and does not mean.
There is genuine adaptation, in the sense that repeated low-level exposure produces some immunity to specific local organisms.
It does not mean the food is safe in an absolute sense, and it does not transfer. A resident's tolerance is specific to what they have been exposed to, which is why people get ill travelling within their own country as well as outside it.
It also does not apply to everything. Some things will make anybody ill regardless of how long they have lived somewhere.
The trade-off I have made
I am not going to pretend I apply this consistently, and it is worth being honest about the calculation.
Some of the best food I have eaten came from carts where I could see several things I would rather not have seen. I ate it anyway, weighing a small risk of a bad day against food I would not otherwise get.
Where I do not take the risk is when the consequences would be disproportionate — before a flight, before something I cannot miss, or when travelling somewhere with poor medical access.
And I am considerably more careful about what I give to children or to anybody older, because the same illness is not the same illness for everybody.
The practical minimum
If somebody wanted one rule rather than an essay, it would be this: eat things that are hot right now, and be careful about everything cold that comes with them.
That single rule accounts for most of the difference in my own experience, and it rules out very little of what makes street food worth eating, since the great majority of it comes off a hot surface anyway.
The things it rules out — the cut fruit, the pre-made cold items, the drink with ice — are also the things that people mostly do not travel for.
The seasonal pattern
One further thing worth knowing. Risk is not constant through the year.
Hot and humid conditions accelerate everything that goes wrong with food left standing, which is why the same stall can be entirely fine in one season and a poor bet in another.
The onset of the rains in particular is when most people I know are more careful, and local advice tends to be quite specific about which months and which foods.
That local knowledge is worth asking about rather than deducing. People who live somewhere generally know which stalls to avoid in July, and they will say so if asked directly.