I’m planning on starting to pack a lunch for work and wondering if it’ll be ok to keep it at my desk unrefrigerated. If I make a sandwich from deli lunch meat (chicken or whatever), will it be safe to eat if it’s in a sealed plastic bag, but at room temperature, for 4-6 hours?
Every day I went to school I did just that. No refrigerators back then. Nor sealed plastic bags. Just wrapping paper and a brown paper bag with an apple as well.
And always remember - that which does not kill you makes you stronger 
This is not scientific by any means, but through eight years of grammar school and four of high school, none of my lunches were refrigerated, and I had tuna salad and lunch meat sandwiches as well as PB&J, and I never had a problem.
Nobody refrigerated their lunches, and those frozen inserts and thermal bags weren’t used by anyone in my class, so I wasn’t the only one eating a lunch that had been sitting in the hall for hours.
I take a lunch to work most days. Often it’s a sandwich, though sometimes it’s leftovers. I could put it in the fridge at work, but I can’t be bothered, so it sits under my desk until noon. Been at this job for eight years, haven’t poisoned myself yet. YMMV.
Depends on the filling. Mashed avocado might last an hour before turning brown; most dry stuff will last a couple of days. Even unwrapped.
Soldiers used to carry stuff for weeks in their knapsacks.
I took a tuna salad sandwich (with hard boiled eggs, pickles and mayo) to school every day for four years and kept it wrapped in wax paper in a brown paper bag in my locker until lunch time. I did not die. There are those who would argue brain damage occurred but that was from boredom of eating the same lunch every day for four years.
I often carry around a couple of sandwiches with meat slices here in Bangkok. Still okay after a few hours.
4-6 hours somewhere under 100 degrees, I see no issue. Unless you have some sort of condition compromising your stomach/gastric system or making you somehow overly sensitive.
You’d be okay with the highly preserved meats like salami and bologna, also ok with peanut butter or cheese. I’d be hesitant about mixtures like chicken salad.
No kidding. That stuff doesn’t even need to be stored refrigerated.
Cooked meats do pretty well, too. But here in Holland we sometimes eat something that’s made of finely ground raw beef. That stuff can turn green in half a day in hot weather.
Don’t worry about this for 4 - 6 hours in normal temperatures.
If you’re concerned, despite what everyone else has said, you can freeze your bread and make your sandwich with frozen slices. They’ll warm up by lunch, but meanwhile will keep your lunch meat cooler than room temperature for several hours.
If you want to feel a bit safer, but not have to remember to bring a frozen insert home, freeze something else in your lunch. Broomstick mentioned your sandwich bread. I used to freeze a Capri Sun or water bottle or one of those little plastic “cans” of fruit. Keeps everything cool.
Beware of lettuce in sandwiches next to condiments all day, though. Weird things can happen.
The danger, if there is one, would be in the mayo. Any other condiment can be left on the shelf opened for weeks or months.
Don’t use mayo and you’ll be fine. Or if you want mayo, get a supply of those little squeezable plastic envelopes like fast food joints use. Those are shelf stable and you can apply the safe mayo to your safe sandwich just before eating.
That’s more or less what I was going to say- it really depends on what the sandwich is made of. Something like a ham sandwich with mustard would keep a lot longer than a egg salad sandwich would.
Homemade mayo, maybe. Commercially prepared mayonnaise, however, is made with pasteurized eggs and has an acidity level high enough to prevent bacterial growth. Salmonella will actually die when directly injected into mayo. It’s actually the mayonnaise that keeps everything else fresh.
For over a decade, I’ve pulled my lunch out of the fridge at 5:40 AM, and kept it at room temperature until noon. Contents: Sandwich with meat and cheese, yogurt, fruit. No food-borne illnesses in nearly 13 years . . .
Food’s much more flavor-rich closer to room temperature anyway.
Here’s the deal with mayonnaise:
Eggs can sometimes be contaminated with salmonella (for widely varying definitions of “sometimes”). Eggs are a major ingredient in mayo. Now, in order for salmonella - or any bacteria - to grow to dangerous levels, it needs water and food. In mayo, there’s plenty of food. Lots of nutritious oils and proteins and whatnot. But because it’s an emulsion, there’s no free water available. This is why we can keep mayo in a jar on the shelf in the grocery store. Even if it’s contaminated, the bacteria can’t reproduce.
The danger comes when you introduce mayo, which might be carrying dormant salmonella, to some other food stuff that brings plenty of free water with it. In practice, this is just about any other ingredient you care to name - meat, bread, etc. Once you put mayo on your sandwich, you’re potentially allowing the bacteria to begin to reproduce. IF the bacteria is there to begin with. That’s why it’s considered dangerous to leave mayo-containing food out at room temperature for long periods of time. That’s also why you need to refrigerate your jar of mayo after you stick your crumb-laden knife into it. (Partly - it also retards oxygenation)
“Ah ha!” I hear myriads of commenters cry, “But I’ve done just that for years and never had a problem!” Yes, yes, I know. It’s not a guarantee of problems; it just makes them possible. As I understand it, the amount of salmonella bacteria found in eggs these days is quite low, though I haven’t seen any hard data in a long time. I’m just trying to explain the reasoning behind the warnings.
there are food safety guidelines (30 to 60 minutes) and there is what millions have lived with for centuries.
there always is a chance for some people. even food not spoiled can be contaminated (just to increase the fear factor).
don’t use mayo.
My lunch comes out of the refrigerator every morning before I leave for the office, and sits on my desk at work until I eat if 4-5 hours later (unless lunch is leftover pizza, in which case it will have been sitting out on the counter at home overnight, before I leave it sitting on my desk all morning). I’ve been doing this for over 16 years at this job, and I haven’t had an issue yet.
Personally I don’t worry one bit about mayonnaise. Commercial mayo contains enough acid that bacterial growth is pretty difficult, and almost certainly was prepared with pasteurized eggs, so the chances of getting salmonella poisoning from your tuna sandwich are pretty darn small. If you make your mayonnaise from scratch at home, using raw eggs, then your experience may differ.
I remember leaving my lunch in my backpack (when backpacks in school were not yet even a new thing) over the weekend. My lunch was fine.
Even today so many decades later, I’ve eaten sandwiches that are 24 hours old, unrefrigerated. Kids are wimpy these days.