# Does semen show up under a black light? **URL:** \ **Category:** Factual Questions\ **Created:** [January 30, 2008, 5:38am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557 "2008-01-30T05:38:47Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Runs\_With\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/278dde/32.png) [@Runs\_With\_Scissors](https://boards.straightdope.com/u/Runs_With_Scissors)\ **Post date:** [January 30, 2008, 5:38am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/1 "2008-01-30T05:38:47Z")
A friend and I were indoors at a place…it was dark, but “black lit.” He said the glowing spots on my t-shirt were semen stains. I say no way, I washed it. What say you? ---
**Author:** ![Pullet](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Pullet](https://boards.straightdope.com/u/Pullet)\ **Post date:** [January 30, 2008, 5:44am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/2 "2008-01-30T05:44:11Z")
So…you haven’t found the answer to this experimentally yet? Pullet _A girl_ ---
**Author:** ![Runs\_With\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/278dde/32.png) [@Runs\_With\_Scissors](https://boards.straightdope.com/u/Runs_With_Scissors)\ **Post date:** [January 30, 2008, 5:44am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/3 "2008-01-30T05:44:43Z")
Aaargh…took too long to edit… It should read like this: A friend and I were indoors at a place…it was dark, but “black lit.” He said the glowing spots on my t-shirt were semen stains. I say no way; I washed it. And that’s the main question…does semen wash out of t-shirts after one typical wash in a washing machine? What other (common) things might have caused the “blacklighted” stains? Inquiring minds 🙂 ---
**Author:** ![Runs\_With\_Scissors](https://avatars.discourse-cdn.com/v4/letter/r/278dde/32.png) [@Runs\_With\_Scissors](https://boards.straightdope.com/u/Runs_With_Scissors)\ **Post date:** [January 30, 2008, 5:46am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/4 "2008-01-30T05:46:53Z")
[QUOTE=Pullet] So…you haven’t found the answer to this experimentally yet? Pullet _A girl_ [/QUOTE] I _would_ but 1978 called and asked for my black light back 🙂 Seriously, though, if I had one I’d perform the test…all in the name of science 🙂 ---
**Author:** ![Pullet](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Pullet](https://boards.straightdope.com/u/Pullet)\ **Post date:** [January 30, 2008, 5:51am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/5 "2008-01-30T05:51:33Z")
You can get a new blacklight for like $12 at Walmart. It’s all in the name of science! Do it! ---
**Author:** ![x-ray\_vision](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/x-ray_vision/32/351_2.png) [@x-ray\_vision](https://boards.straightdope.com/u/x-ray_vision)\ **Post date:** [January 30, 2008, 5:52am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/6 "2008-01-30T05:52:28Z")
> [@](#): > > _What other substances glow under a black light?_ > > Urine, porphyrin, semen, sperm and saliva fluoresce under a blacklight. > **[Rats under a black light](http://www.ratbehavior.org/BlackLight.htm)** ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [January 30, 2008, 5:57am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/7 "2008-01-30T05:57:53Z")
I’d like to reiterate something I’ve mentioned over and over. People always think all the stains on the comforter/tshirts/walls etc etc that glow under a black light are seman. Well, laundry detergent glows also. The stains on your tshirt or probably just left over laundry detergent. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 30, 2008, 6:01am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/8 "2008-01-30T06:01:55Z")
Almost any organic material will glow, to some extent, under a black light. The stains on your shirt could equally well have been drool, or food, or blood, or possibly sweat (I’m not sure about that one). You know better than we would how recently you would have been in contact with any of those substances. ---
**Author:** ![Wile\_E](https://avatars.discourse-cdn.com/v4/letter/w/c37758/32.png) [@Wile\_E](https://boards.straightdope.com/u/Wile_E)\ **Post date:** [January 30, 2008, 6:16am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/9 "2008-01-30T06:16:23Z")
I heard club soda glows, too. Did you have something with club soda that you spilled on yourself? Was this a club that stamps your hand so you can get back in if you leave? Because they usually use a fluorescent ink and if you rubbed it on your shirt then it would glow. Highlighter ink also glows. ---
**Author:** ![Harmonix](https://avatars.discourse-cdn.com/v4/letter/h/3ec8ea/32.png) [@Harmonix](https://boards.straightdope.com/u/Harmonix)\ **Post date:** [January 30, 2008, 10:38am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/10 "2008-01-30T10:38:26Z")
I second the laundry detergent Idea. Too lazy to find a cite right now, but I believe Modern Laundry detergent contains phosphorous to ‘make your whites whiter and your colors brighter’. It shows up under a black light as glowing specks on your shirt. ---
**Author:** ![An\_Gadai](https://avatars.discourse-cdn.com/v4/letter/a/d6d6ee/32.png) [@An\_Gadai](https://boards.straightdope.com/u/An_Gadai)\ **Post date:** [January 30, 2008, 10:53am UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/11 "2008-01-30T10:53:51Z")
Also, jip stains are nearly impossible to get rid of. 😃 ---
**Author:** ![Radegast](https://avatars.discourse-cdn.com/v4/letter/r/c4cdca/32.png) [@Radegast](https://boards.straightdope.com/u/Radegast)\ **Post date:** [January 30, 2008, 12:41pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/12 "2008-01-30T12:41:38Z")
A little off topic but I encountered a bathroom in a Dublin pub that was heavily black-lit, and urine certainly flouresces. ---
**Author:** ![brewha](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@brewha](https://boards.straightdope.com/u/brewha)\ **Post date:** [January 30, 2008, 12:52pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/13 "2008-01-30T12:52:38Z")
[Mitch Hedberg] I was under the impression that that mustard stain came out. [/MH] ---
**Author:** ![Solfy](https://avatars.discourse-cdn.com/v4/letter/s/848f3c/32.png) [@Solfy](https://boards.straightdope.com/u/Solfy)\ **Post date:** [January 30, 2008, 2:05pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/14 "2008-01-30T14:05:37Z")
Many detergents contain additives that are UV active. They enhance the whiteness of your whites. Without having actual experimental evidence, I’d wager that most _ahem_ protein based stains should come out under normal washing conditions. ---
**Author:** ![flurb](https://avatars.discourse-cdn.com/v4/letter/f/51bf81/32.png) [@flurb](https://boards.straightdope.com/u/flurb)\ **Post date:** [January 30, 2008, 2:06pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/15 "2008-01-30T14:06:34Z")
Do you have any reason to believe that they ARE semen stains on your shirt? ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [January 30, 2008, 2:10pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/16 "2008-01-30T14:10:17Z")
[QUOTE=flurb] Do you have any reason to believe that they ARE semen stains on your shirt? [/QUOTE] I took the statement “No way, I washed it” as evidence to support a “yes” answer to that question. ---
**Author:** ![lieu](https://avatars.discourse-cdn.com/v4/letter/l/c2a13f/32.png) [@lieu](https://boards.straightdope.com/u/lieu)\ **Post date:** [January 30, 2008, 2:23pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/17 "2008-01-30T14:23:32Z")
Nevermind. ---
**Author:** ![WhyNot](https://avatars.discourse-cdn.com/v4/letter/w/c77e96/32.png) [@WhyNot](https://boards.straightdope.com/u/WhyNot)\ **Post date:** [January 30, 2008, 2:36pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/18 "2008-01-30T14:36:27Z")
[QUOTE=Wile E] I heard club soda glows, too. [/QUOTE] I don’t think it’s club soda, but _tonic water_ that you’re thinking of. The quinine in tonic water glows under black light. Club soda’s just water and CO[sub]2[/sub], sometimes with salt or baking soda. [QUOTE=brewha] [Mitch Hedberg] I was under the impression that that mustard stain came out. [/MH] [/QUOTE] [_Once More, With Feeling_] ♫They got the mustard OOOOOUUUUUUT!♫ ♫(They got the mu-stard out!) ♫ [_/Once More, With Feeling_] My vote is also for detergent. Sounds like you’re packing your washing machine too full for a good rinse cycle, and it’s leaving stuff behind. ---
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [January 30, 2008, 4:23pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/19 "2008-01-30T16:23:02Z")
Maybe the cat is humping your laundry. ---
**Author:** ![Mr.Slant](https://avatars.discourse-cdn.com/v4/letter/m/c57346/32.png) [@Mr.Slant](https://boards.straightdope.com/u/Mr.Slant)\ **Post date:** [January 30, 2008, 4:25pm UTC](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557/20 "2008-01-30T16:25:41Z")
There was a nice Youtube video along these lines. A young lady was at a party, dancing as you please… one of her girlfriends pulled her aside and she left. The young lady had a bright spot spreading beneath her skirt… and glowing on the left side of her mouth… [Next page](https://boards.straightdope.com/t/does-semen-show-up-under-a-black-light/435557.md?page=2)