# Any substances that are harmless alone, but when combined become fatal?
**URL:** https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031
**Category:** Factual Questions
**Created:** [February 18, 2015, 7:32pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031 "2015-02-18T19:32:41Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@iiandyiiii](https://boards.straightdope.com/u/iiandyiiii)
#### Post date: [February 18, 2015, 7:32pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/1 "2015-02-18T19:32:41Z")
In case the title isn’t clear, are there any substances in which, when consumed in a moderate amount by themselves are harmless or nearly harmless to human health, but if consumed together (or if one is consumed today and another consumed tomorrow) can be fatal?
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### Author:  [@DataX](https://boards.straightdope.com/u/DataX)
#### Post date: [February 18, 2015, 7:38pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/2 "2015-02-18T19:38:42Z")
We’ll ink cap mushrooms and alcohol?
Neither one will kill you (although I’m not sure the ink cap would be great on its own) - but drink some alcohol slightly after and you can die.
Plenty of multiple drug interactions as well.
Also MAOI with favs beans, sauerkraut, chianti, and a bunch of other stuff with tyromine can cause a hypotensive(or hyper - don’t remember) crisis which you could theoretically die from.
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### Author:  [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)
#### Post date: [February 18, 2015, 7:48pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/3 "2015-02-18T19:48:44Z")
Don’t mix bleach and ammonia.
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### Author:  [@iiandyiiii](https://boards.straightdope.com/u/iiandyiiii)
#### Post date: [February 18, 2015, 7:50pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/4 "2015-02-18T19:50:24Z")
> [@DataX](#):
>
> We’ll ink cap mushrooms and alcohol?
>
> Neither one will kill you (although I’m not sure the ink cap would be great on its own) - but drink some alcohol slightly after and you can die.
>
> Plenty of multiple drug interactions as well.
>
> Also MAOI with favs beans, sauerkraut, chianti, and a bunch of other stuff with tyromine can cause a hypotensive(or hyper - don’t remember) crisis which you could theoretically die from.
Thanks – for some reason I didn’t think of drug interactions.
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### Author:  [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)
#### Post date: [February 18, 2015, 8:00pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/5 "2015-02-18T20:00:45Z")
Vinegar and baking soda. 🙂
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### Author:  [@astorian](https://boards.straightdope.com/u/astorian)
#### Post date: [February 18, 2015, 8:02pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/6 "2015-02-18T20:02:20Z")
Well, Carbon and Oxygen individually are harmless, but Carbon Dioxide can be poisonous and Carbon Monoxide is deadly.
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### Author:  [@AClockworkMelon](https://boards.straightdope.com/u/AClockworkMelon)
#### Post date: [February 18, 2015, 8:04pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/7 "2015-02-18T20:04:43Z")
> [@nearwildheaven](#):
>
> Don’t mix bleach and ammonia.
'Cause each of these is totally harmless alone.
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### Author:  [@buddy431](https://boards.straightdope.com/u/buddy431)
#### Post date: [February 18, 2015, 8:13pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/8 "2015-02-18T20:13:59Z")
> [@astorian](#):
>
> Well, Carbon and Oxygen individually are harmless, but Carbon Dioxide can be poisonous and Carbon Monoxide is deadly.
And yet, you’re breathing both at the same time, and it’s not doing a thing to you.
[QUOTE=nearwildheaven]
Don’t mix bleach and ammonia.
[/QUOTE]
Bleach and ammonia are both plenty toxic on their own, and honestly the things you get by mixing them (chloroamine, mostly) aren’t markedly worse than the starting materials
Drug interactions, either with each other, with alcohol, or with food, are probably the best you’re going to get.
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### Author:  [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)
#### Post date: [February 18, 2015, 9:30pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/9 "2015-02-18T21:30:01Z")
Melamine combined with cyanuric acid forms a structure that screws up your kidneys. I don’t think either is considered harmless alone though, but combined I believe they are worse than either ingredient alone.
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### Author:  [@Cartoonacy](https://boards.straightdope.com/u/Cartoonacy)
#### Post date: [February 18, 2015, 9:48pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/10 "2015-02-18T21:48:01Z")
I don’t have a copy, but [Deadly Doses](http://www.amazon.com/Deadly-Doses-Writers-Poisons-Howdunit/dp/0898793718) is the reference book you need for questions like this.
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### Author:  [@Canadjun](https://boards.straightdope.com/u/Canadjun)
#### Post date: [February 18, 2015, 10:34pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/11 "2015-02-18T22:34:47Z")
See [Binary Chemical Weapon](http://en.wikipedia.org/wiki/Binary_chemical_weapon).
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### Author:  [@Senegoid](https://boards.straightdope.com/u/Senegoid)
#### Post date: [February 19, 2015, 4:54am UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/12 "2015-02-19T04:54:37Z")
Gaseous hydrogen: Not particularly harmful.
Gaseous oxygen: Not particularly harmful, when inhaled in moderate doses. Required for animal life, in fact. Excessive doses could be caustic, however.
Combine the two in certain proportions, and you get ( **Gasp!** ) the deadly, ghastly Dihydrogen Monoxide!
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### Author:  [@SimonMoon5](https://boards.straightdope.com/u/SimonMoon5)
#### Post date: [February 19, 2015, 3:17pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/13 "2015-02-19T15:17:25Z")
Pop Rocks and soda. 🙂
I know it’s true. An urban legend told me so!
And maybe Mentos and Diet Coke?
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### Author:  [@astorian](https://boards.straightdope.com/u/astorian)
#### Post date: [February 19, 2015, 3:23pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/14 "2015-02-19T15:23:05Z")
> [@SimonMoon5](#):
>
> Pop Rocks and soda. 🙂
>
> I know it’s true. An urban legend told me so!
>
> And maybe Mentos and Diet Coke?
Well, a roll of Mentos and a 3 liter Diet Coke definitely DO make a fantastic backyard geyser! That’s one of my son’s favorite “experiments.”
(That and creating bombs by putting dry ice iand warm water n a soda bottle.)
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### Author:  [@vomit\_comet](https://boards.straightdope.com/u/vomit_comet)
#### Post date: [February 19, 2015, 5:11pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/15 "2015-02-19T17:11:24Z")
Potassium Permanganate and Glycerin.
Water, Sugar and Yeast. Produces C02, if the C02 is allowed to collect in a low depression and displace the oxygen it could suffocate.
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### Author:  [@vomit\_comet](https://boards.straightdope.com/u/vomit_comet)
#### Post date: [February 19, 2015, 5:12pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/16 "2015-02-19T17:12:58Z")
> [@Senegoid](#):
>
> Gaseous hydrogen: Not particularly harmful.
>
> Gaseous oxygen: Not particularly harmful, when inhaled in moderate doses. Required for animal life, in fact. Excessive doses could be caustic, however.
>
> Combine the two in certain proportions, and you get ( **Gasp!** ) the deadly, ghastly Dihydrogen Monoxide!
Only after a certain, possibly devastating explosion.
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### Author:  [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)
#### Post date: [February 19, 2015, 5:19pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/17 "2015-02-19T17:19:03Z")
> [@nearwildheaven](#):
>
> Don’t mix bleach and ammonia.
> [@AClockworkMelon](#):
>
> 'Cause each of these is totally harmless alone.
It’s the gas that is produced when you mix them that is the additional danger that isn’t present when merely cleaning with bleach or ammonia by themselves. You can easily be working around either bleach or ammonia by themselves and not be in danger of passing out from the fumes. See post 11.
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### Author:  [@CGav8r](https://boards.straightdope.com/u/CGav8r)
#### Post date: [February 19, 2015, 5:51pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/18 "2015-02-19T17:51:50Z")
Alcohol combined with desperation has proven fatal, (and at the very least, has contributed to Coyote Love on many occasions).
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### Author:  [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)
#### Post date: [February 19, 2015, 6:23pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/19 "2015-02-19T18:23:55Z")
> [@AClockworkMelon](#):
>
> 'Cause each of these is totally harmless alone.
Dihydrogen monoxide can cause fatal reactions when used improperly, too.
:eek:
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### Author:  [@Aspenglow](https://boards.straightdope.com/u/Aspenglow)
#### Post date: [February 19, 2015, 6:34pm UTC](https://boards.straightdope.com/t/any-substances-that-are-harmless-alone-but-when-combined-become-fatal/713031/20 "2015-02-19T18:34:22Z")
The one I always think of is Tylenol with alcohol. More than a few people have done in their livers with this seemingly harmless combination.
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