# Are sweat, tears and saliva blood? **URL:** \ **Category:** Factual Questions\ **Created:** [June 11, 2015, 11:13pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300 "2015-06-11T23:13:05Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![protoboard](https://avatars.discourse-cdn.com/v4/letter/p/fbc32d/32.png) [@protoboard](https://boards.straightdope.com/u/protoboard)\ **Post date:** [June 11, 2015, 11:13pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/1 "2015-06-11T23:13:05Z")
Or more accurately, are they derived from the blood? I know urine is, and I know lymph is essentially blood plasma (or you could say, blood is lymph with red cells!). Where does spit, sweat and tears come from? Also, is breast milk a blood product? ---
**Author:** ![cwthree](https://avatars.discourse-cdn.com/v4/letter/c/9de0a6/32.png) [@cwthree](https://boards.straightdope.com/u/cwthree)\ **Post date:** [June 11, 2015, 11:34pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/2 "2015-06-11T23:34:16Z")
Breast milk is secreted by milk-producing glands. All of the components needed to make milk are delivered to the glands via the blood. I suppose you could say that milk is a blood product. Orthodox rabbis, who have spent centuries discussing milk and blood, would disagree with you, though. I would have to disagree as well. Everything is a mammal’s body is, ultimately, made from substances delivered via the bloodstream. That doesn’t mean they’re blood products. That would be like saying that the strawberries on my cereal are a highway product or a truck product because they were delivered via a truck that was driven on the highway. ---
**Author:** ![Senegoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/senegoid/32/6606_2.png) [@Senegoid](https://boards.straightdope.com/u/Senegoid)\ **Post date:** [June 11, 2015, 11:37pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/3 "2015-06-11T23:37:17Z")
I don’t know if sweat, tears and saliva are blood derivatives (in the sense that I think you mean, like urine is just blood with some stuff filtered out of it). But I learned in Intro Biology that the mammary glands are just specialized sweat glands. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [June 12, 2015, 1:32pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/4 "2015-06-12T13:32:42Z")
Urine isn’t derived from the blood. It contains waste products that the blood carries to the kidneys, but no actual blood, unless you have kidney problems. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [June 12, 2015, 1:41pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/5 "2015-06-12T13:41:00Z")
In the sense that these things are made from components that were carried by blood at one point, then yes, all of these things are made of blood. However, by that standard, you have to also say that our muscles, organs, hair…everything we are made of are also made of blood. So it’s not a terribly interesting thing to point out. ---
**Author:** ![Ornery\_Bob](https://avatars.discourse-cdn.com/v4/letter/o/da6949/32.png) [@Ornery\_Bob](https://boards.straightdope.com/u/Ornery_Bob)\ **Post date:** [June 12, 2015, 2:13pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/6 "2015-06-12T14:13:11Z")
Tears, sweat and saliva all come from beer. Sheesh! ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [June 12, 2015, 2:22pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/7 "2015-06-12T14:22:03Z")
Since sweat, tears, and saliva are all water based and that water can only come from the food and liquids you take in, why not say they are mouth-based, or stomach based, or small intestine based, or colon based? That type of reductionism is simply not a useful way of thinking about it. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [June 12, 2015, 3:10pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/8 "2015-06-12T15:10:35Z")
I guess a more useful thing would be to say - is there anything in sweat, tears or breast milk that is not in blood? Urine is clearly stuff that is removed from the bloodstream, and does not contain additional manufactured components. In that sense it is derived from blood. The components in sweat are similarly only those things found in the blood. Water, salts, urea, etc, but usually at lower concentrations than in the blood. Tears however contain a wide range of components that are not present in blood, and are manufactured for purpose. They protect, lubricate, nourish and disinfect the cornea. As noted, the raw materials for these additional components are delivered by the blood. By they are not present in the blood. Breast milk is more of the same. The water and electrolytes are clearly derived unchanged from the blood supply. But the rest of the contents of milk is generated in the breasts and is not in any useful sense directly derived from the blood. For instance, both tears and breast milk contain Immunoglobulin A (IgA) which is not derived from the blood. ---
**Author:** ![Claverhouse](https://avatars.discourse-cdn.com/v4/letter/c/13edae/32.png) [@Claverhouse](https://boards.straightdope.com/u/Claverhouse)\ **Post date:** [June 12, 2015, 5:00pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/9 "2015-06-12T17:00:23Z")
The Blood is the Life. ---
**Author:** ![gigi](https://avatars.discourse-cdn.com/v4/letter/g/a587f6/32.png) [@gigi](https://boards.straightdope.com/u/gigi)\ **Post date:** [June 12, 2015, 9:42pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/10 "2015-06-12T21:42:01Z")
Could the OP be referring to a concern about these substances carrying “blood-borne” diseases? ---
**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\ **Post date:** [June 13, 2015, 2:29pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/11 "2015-06-13T14:29:16Z")
[QUOTE=Count Dracula] I vant to dreenk your sweat, er urine, uh breast milk, bloood, that’s eet. Bloood. [/QUOTE] It’s hard to type a Dracula impression. ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [June 13, 2015, 4:16pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/12 "2015-06-13T16:16:03Z")
> [@Francis\_Vaughan](#): > > I guess a more useful thing would be to say - is there anything in sweat, tears or breast milk that is not in blood? Urine is clearly stuff that is removed from the bloodstream, and does not contain additional manufactured components. In that sense it is derived from blood. I want to congratulate you for making sense out of a poorly worded OP. **protoboard** , take notes on how to explain yourself more clearly. ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [June 13, 2015, 4:35pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/13 "2015-06-13T16:35:03Z")
I’m now picturing glands as little factories, though… “manufactured” sure isn’t the word I would have chosen. It sounds like someone had an overdose of [Once upon a time… life](https://www.youtube.com/watch?v=mpchye1X_Rs) :). ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [June 13, 2015, 5:21pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/14 "2015-06-13T17:21:42Z")
Saliva must have been the sax player. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [June 13, 2015, 6:02pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/15 "2015-06-13T18:02:07Z")
**Moderator Note** > [@BigT](#): > > I want to congratulate you for making sense out of a poorly worded OP. **protoboard** , take notes on how to explain yourself more clearly. You’re pushing the limits towards a junior modding warning. Don’t do this again. If you don’t like the way that someone words their posts, take it to the Pit. No warning issued. ---
**Author:** ![Drunky\_Smurf](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drunky_smurf/32/449_2.png) [@Drunky\_Smurf](https://boards.straightdope.com/u/Drunky_Smurf)\ **Post date:** [June 15, 2015, 3:40pm UTC](https://boards.straightdope.com/t/are-sweat-tears-and-saliva-blood/722300/16 "2015-06-15T15:40:14Z")
> [@Ornery\_Bob](#): > > Tears, sweat and saliva all come from beer. Sheesh! Especially after falling down.