Bright pink stains on bedsheets - bacteria?

[Hungrycaterpillarsmummy]

I first noticed this a few weeks ago where my 5yr old son's bedsheet had pink marks all over it and I actually assumed we had spilled some Calpol or something on it.
But since I washed the sheets I just spotted some nore on his bedsheets which definitely wasn't there when I put it on. The other thing is he comes to my bed most nights and I just noticed a pink spot on my bedsheets now! It smells..not of Calpol let's put it that way! So a quick Google tells me it could be some kind of non harmful bacteria or if you take certain medication, if you sweat then it can turn pink but I just wondered if anyone actually has any experience of this?!
My son does take sodium Pico sulphate to make him poo as he witholds it.
Here is a photo of one small patch

www.gardenweb.com/discussions/3667746/bright-pink-stains-on-washed-clothes-help

It's a chemical reaction - nothing to worry about but ready the page here and there is a person that runs a laundry that knows - photo of her comment attached. Sun gets rid of it .

Photo won't attach but still down about 12 posts and a lady seems to know.

Sorry it's about 30 posts down by a lady called Suzie

I dyed my son's shirts pink by bleaching them. The yellowed sweat stains turned bright pink. Only sorted by through washing and leaving in the sun to bleach naturally.

Oh I also just thought! My son sometimes has a tablet to chew to show up any areas of his teeth he hasn't brushed properly. That goes blue or pink and he definitely had a tablet last night. I bet it's from those blooming things!

Sounds like you’re getting to the bottom of it but otherwise we get similar but more colours - where my dc has drawn on herself in pen!!!