# Dangerous mayonnaise? **URL:** \ **Category:** Factual Questions\ **Created:** [June 8, 2005, 2:44pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456 "2005-06-08T14:44:07Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [June 8, 2005, 2:44pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/1 "2005-06-08T14:44:07Z")
I’ve been told by a lot of people never to leave mayonnaise, or foodstuffs including mayonnaise, unrefrigerated because there’s a high risk of foodborne illnesses. These warnings especially come during picnics at which potato salad or somesuch thing is served. I can’t for the life of me figure out why this would be the case, though. Looking at the typical ingredients of mayonnaise – eggs, oil, vinegar, salt, lemon juice, mustard powder, other spices – they all seem like things you can safely take with you to a picnic and safely leave unrefrigerated for hours, even days at a time. So what’s up with dangerous mayo? ---
**Author:** ![SpaceDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/spacedog/32/9932_2.png) [@SpaceDog](https://boards.straightdope.com/u/SpaceDog)\ **Post date:** [June 8, 2005, 2:55pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/2 "2005-06-08T14:55:31Z")
> [@acsenray](#): > > I can’t for the life of me figure out why this would be the case, though. Looking at the typical ingredients of mayonnaise – eggs, oil, vinegar, salt, lemon juice, mustard powder, other spices – they all seem like things you can safely take with you to a picnic and safely leave unrefrigerated for hours, even days at a time. > > So what’s up with dangerous mayo? The worry is that people will [dip their clothes in it](http://boards.straightdope.com/sdmb/showthread.php?t=319686) when you’re not looking. Sorry, couldn’t resist. The eggs in mayo are uncooked as I understand it, therefore the whole thing is probably a breeding ground for any bacteria that was in the eggs. This would be slowed if the mayo was kept cool enough. But I suspect the wisdom comes from homemade mayo which would spoil if left out and could probably get quite dangerous due to the bacteria I’d guess that shop bought mayo is treated to prevent these problems – particularly as I’ve seen mayo and things with mayo on them sold unchilled in shops. SD ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 8, 2005, 2:57pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/3 "2005-06-08T14:57:15Z")
Mixing is the problem - food poisoning bacteria need all the right things together in the same place - food, moisture, warmth (and _time_). Ordinary mayonnaise on it’s own is usually OK though, as it doesn’t actually contain a great deal of water (although low fat versions _do_) and it is acidic. The problem with potato salad, however, is that it does contain a lot of water - add moist, usually slightly warm potatoes to mayonnaise and it also dilutes the acidity - you then have everything you need for rapid growth of pathogenic bacteria. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 8, 2005, 2:58pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/4 "2005-06-08T14:58:37Z")
And of course mayo in the jar, unchilled on the shelf is probably aseptic - this isn’t the case as soon as you have opened it. ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [June 8, 2005, 4:25pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/5 "2005-06-08T16:25:23Z")
I heard someone theorizing once that the salad danger might come from cutting board contamination by uncooked chicken used to prepare other picnic foods rather than the mayonnaise. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [June 8, 2005, 5:20pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/6 "2005-06-08T17:20:00Z")
The concern is with Salmonella bacteria that can be present in eggs. Because the eggs in mayo aren’t cooked, there could be live bacteria in the mayo. Now, because mayonnaise is an emulsion, there’s no water available for the bacteria to grow, so typically, in clean, unmixed mayo any bacteria present won’t be able to grow to dangerous levels. However, once you mix it with, say, potato salad, or you stick your crumb-laden knife into the jar, leaving some crumbs behind, you have potentially combined harmful bacteria with a food and water source. If you let it sit at a comfortable temperature, that’s bad news. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 8, 2005, 7:31pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/7 "2005-06-08T19:31:32Z")
Salmonella isn’t the only food poisoning bacteria that will thrive on foods like potato/mayonnaise salad - others such as staphylococcus, clostridium and campylobacter can be just as nasty and no raw chicken is required to cross-contaminate the food - these bacteria are naturally abundant on/in our bodies and in our environment. Of course just introducing a small sample of them into the food isn’t a problem - you ingest these bacteria in small quantities every time you put your finger (even when it is quite clean) into your mouth. The problem happens when the bacteria get into the food (which is almost inevitable), then it’s left at room temperature for half a day before it is eaten. ---
**Author:** ![Excalibre](https://avatars.discourse-cdn.com/v4/letter/e/898d66/32.png) [@Excalibre](https://boards.straightdope.com/u/Excalibre)\ **Post date:** [June 8, 2005, 7:32pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/8 "2005-06-08T19:32:35Z")
No cite handy, because I got this from an Ann Landers column many years ago. Someone wrote to ask if it was okay to keep mayonnaise out of the fridge after opening. She contacted a company that sold it, and while they recommend refrigeration, it’s not actually necessary. However, once mixed with other foods it provides an excellent medium for bacteria. ---
**Author:** ![daffyduck](https://avatars.discourse-cdn.com/v4/letter/d/ec9cab/32.png) [@daffyduck](https://boards.straightdope.com/u/daffyduck)\ **Post date:** [June 8, 2005, 7:40pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/9 "2005-06-08T19:40:35Z")
“The Centers for Disease Control and Prevention estimates that 76 million cases of food poisoning occur each year in the United States,” said Dr. Lipsman. “Although most cases are relatively mild, foodborne illness results in 325,000 hospitalizations and 5,000 deaths each year.” ---
**Author:** ![Acsenray](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/acsenray/32/4519_2.png) [@Acsenray](https://boards.straightdope.com/u/Acsenray)\ **Post date:** [June 8, 2005, 8:20pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/10 "2005-06-08T20:20:53Z")
I wonder, though, to what extent this problem is attributable to mayonnaise. It seems to me that any foodstuff can be a good host to foodborne illnesses. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [June 8, 2005, 10:17pm UTC](https://boards.straightdope.com/t/dangerous-mayonnaise/307456/11 "2005-06-08T22:17:13Z")
> [@acsenray](#): > > I wonder, though, to what extent this problem is attributable to mayonnaise. It seems to me that any foodstuff can be a good host to foodborne illnesses. [Check this link.](http://www.dressings-sauces.org/foodsafety_picnic.html). Admittedly, it’s from the American Association of Dressings and Sauces, so perhaps not the most unbiased source. > [@](#): > > And, despite what your mother may have told you, mayonnaise does not increase the chances of food poisoning. In fact, commercially prepared mayonnaise actually contains ingredients that protect against bacteria. It’s homemade mayonnaise recipes using unpastuerized eggs that gave birth to the myth that mayonnaise causes food poisoning. > …“Commercial mayonnaise products are made with pasteurized eggs in a high-acid environment that slows, even inhibits, bacterial growth. It’s the low-acid ingredients (chicken, ham, potatoes) that are often mixed with mayonnaise which are most susceptible to the growth of food poisoning bacteria and must be handled properly for a safe and happy picnic” she reports.