What is the science behind evaps?

[Confusedddddddd]

Just a curious question, and wondering if anyone can answer it? I'm done some Googling but can't seem to find a definite answer.

I know I shouldn't be testing early, and I know I certainly shouldn't be looking back at tests after 5 minutes. I know I'm not pregnant, but I'm curious.

For me, I've had an occasion a few months ago where I had evap lines for the first time on Easy@Home tests. Over the course of 24 hours and 3 wee samples the lines got darker - none appeared within the 5 mins. The final one I also tested with a boots early test and also ended up with an evap line. Then my period started within the hour 3 days early at 9dpo instead of 12dpo.

I've been using the same tests from the same batch and others since and never an evap line.
Until this month, late 7/8dpo I decided to test, I thought I could see something but it was late my eyes were tired and the light not great so left the test out on the side and figured I'll check in the daylight, there was a line. Tested again 24 hours later - negative. But out of pure curiosity decided to check it again in the morning and once again there's a faint line but slightly darker than the previous days.
I'm now fully expecting my period to start early and know they're invalid etc. but curious to know what in the urine causes this to happen?

https://www.peeonastickfreak.com/tag/run/

this explains it well

Yeh that's one that's I've seen, but doesn't truly explain the science. Every evap I've had has been pink - and a full thickness line. I'm wondering what molecules are reacting with each other? Every pregnancy test eventually dries but why to some have reactions in the drying process and not others?

I've read that some really bad UTIs can turn a pregnancy test positive.

Apologies for my brain just going whhhhhyyyy?

The first set of evaps I had - I assumed it was to do with the fact maybe a bit of blood got in the sample and that's what caused it (as it got darker as my period started), but the couple of times were not close to period.

I’ve only just started with easy @ home and done about 6 tests so far last cycle. Not even had a hint of an indent so maybe you have a different batch.
i thought wondfo were good until i got loads of nasty faint false lines too.
i take these cheap tests as something to use before you use an expensive on FRER or Clearblue digital.
i can’t imagine the money I’d spend taking frers all month! Some people do though.