My partner is pregnant, and thought perhaps she was going mad when one day she found our toilet seat had turned blue. After some investigation, it seems this is a real phenomena, see here for a nice example, with the image from this link shown below.

Toilet seat turned blue

One explanation suggested is dye transfer from new maternity jeans, however we find this unlikely for a variety of reasons:

  • This is late pregnancy and the jeans have been worn for some time without this effect.
  • My partner assures me she takes her trousers off to go to the toilet, and even her underwear, and there is not a white patch where the underwear would have been (and therefore no dye transfer)

The phenomenon is also described as possibly relating to taking certain pharmaceuticals for Crohn's disease. My partner happens to take (Sulfasalazine) which is used for this (although it's not what she's taking it for) and she's never encountered this before, despite taking them for some time. Another suggestion we've seen is that it is from the dye in a batch of pregnancy vitamin tablets she's started taking, which are indeed blue, although, she's also been taking these daily for a month or so.

However, we don't know the answer, and these are just ideas, so why has our toilet seat turned blue?!

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    $\begingroup$ Whoever voted to close this as a medicine question, please provide your reasoning. As far as I know, toilet seats won’t visit doctors (and aren’t concerned about their health). $\endgroup$ – Jan Oct 15 '16 at 14:10
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    $\begingroup$ @bon, It's definitely about chemistry, I want to know what chemical reaction is causing this. If you suggest there's gamma rays shooting from her posterior and ionising the seat to cause this effect, or something like this I'll happily move it to Physics, but its hardly medicine. I originally gave it the tag 'biochemistry'. $\endgroup$ – crobar Oct 15 '16 at 15:05
  • $\begingroup$ Would like to know any reasons for downvoting this question so I can improve it thanks! I don't see any immediate problems with how it is presented, and it is a genuine question. $\endgroup$ – crobar Oct 15 '16 at 22:19
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    $\begingroup$ Unanswerable via internet most probably. $\endgroup$ – Mithoron Oct 15 '16 at 22:38
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    $\begingroup$ OK, I gave it a little though and I think that the most probable answer is that some drug or dietary product is excreted with the sweat, which causes the coloration, as you suggested. Sulfasalazine is known to excrete with bodily fluids, but it is orange. It may be some metabolite of it. The other culprit is that vitamin supplement. I suggest you to take one tablet, dissolve it in water and apply a few drops on a white part of the toilet seat. If the polymer will absorb the dye and turn blue, then that's your answer. $\endgroup$ – vapid Oct 17 '16 at 12:13

The question cannot be answered without a chemical analysis.

However, given that there exist toilet seats with silver based anti-microbial coatings, the bluish grey color may come from metallic silver particles produced by a reduction process similar to the photographic development process.

You could proof the presence of silver by applying Caffenol, an alkaline aqueous solution of instant coffee, washing soda, and vitamin C (ascorbic acid) to the toilet seat. I suggest to use Caffenol-C-M whose preparation is described here. Let the Caffenol react on the toilet seat as long as possible. If grey or black stains are formed that persist after cleaning, your toilet seat contains silver with high probability. Note that the stains cannot be removed anymore.

If the test is positive, the next step would be to investigate why your pregnant partner has reducing powers.

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    $\begingroup$ Now that we actually have the baby, finding time to investigate these things is a bit more difficult, but I'll look at the link you gave. $\endgroup$ – crobar May 10 '17 at 11:38

I do not know the chemical process. I do know it is triggered by a change in hormone levels and appears to be more extreme when vitamin b levels change as well. Chromhidrosis is a condition that causes visibly blue sweat. However, you would see blue staining on her clothing and bed sheets as well. Hormone changes can cause temporary pseudochromhidrosis. This condition produces clear sweat which reacts with certain surface bacteria and the result on some surfaces is blue/purple staining. Only an acid based cleaner will remove it.

  • $\begingroup$ The sheets and so on definitely were not affected, but you second explanation is worth investigating. $\endgroup$ – crobar May 10 '17 at 11:40

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