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And now for the famous 'evaporation lines' that so many people – and 'experts' talk about. To start-with, no evaporation line will be coloured (pink or blue etc. depending on the test you used). Only the HCG can combine with the pregnancy-assay molecules and bring about a colour-change. So if the line is coloured – no matter how faint the line is – then HCG made the line change colour – nothing else! However, just like the wet tissue-paper we talked about earlier, if the area is simply wet with urine, the pregnancy strip may possibly turn a little 'grey' – like a 'shadowy' colour; but if there is no pink or blue colour, then no HCG has been detected. However, remember that the area of the test-stick that you 'wee' on is made of a very dense material, and urine will be absorbed by this dense material and will travel along the test-stick by 'passive-diffusion'.

And liquids like to move from an area of their high concentration – to an area of their low concentration, so, because the test-stick is sealed and dry, the urine will travel along it – to it's other end – and may 'drip-out' inside the sealed area of the stick (the bit after the test and control areas that you cannot see). So the urine will keep moving until the end that you 'wee'd' on has no more urine to offer! Then the 'concentration gradient' ceases and the 'diffusion' will stop. And in most cases, test-sticks – especially those with caps on – can stay wet for days! So if you go back to the stick an hour, or two, or three or four hours etc after the test; and the 'pregnancy' strip has changed colour (pink or blue depending on the test etc), then, whilst the urine has spent several hours travelling up the stick from one end to it's other – and 'dripping out at the other end – the urine has been passing over the 'pregnancy' area all the while.

Therefore, even if the HCG levels are virtually undetectable (but present in minute quantities), as the urine travels over the pregnancy-assay, the HCG will still be attracted-to (remember the 'chemotaxis' we talked about earlier) and will bind with the molecules in the pregnancy-assay – hence a positive coloured line showing up to several hours after the test was done. Like I said, no other molecule or hormone will make the pregnancy-assay change colour – except HCG. So, if after an hour, or several hours, you have a coloured line in any way, then HCG has been detected – and HCG can only be found in your urine if an egg has been fertilised.

So let's not have any more if this 'evaporation line' confusion. If it's slightly grey or remains white – however long after the test you look - then no HCG is present. But if it 's coloured – then HCG is present – in whatever concentration – because only HCG can bring about the colouration of pink/blue, depending on the test you are using. And finally, some tests don't dry out for days – sometimes many days (especially those that you put the caps back on) - so the water-content of the urea has not even evaporated – yet people still go on about 'evaporation lines' – which, in my opinion, is nonsense. And for the record, my Wife's test had a coloured line several hours after we did the test – and I knew she was pregnant – despite the articles I read on the internet about evaporation lines.

And indeed, the next tests proved that she was. I am critically aware of the intense emotions involved when people are hoping or trying to become pregnant - and I hate to think of the emotional heartache and anxieties that these mixed or uncertain test-results can cause - hence the reason for taking the time to write this short article. I hope it helps, and feedback - whether positive or otherwise - is always useful. Take care - and lots of baby-dust - to all prospective Mums-n-Dads

Btw a man wrote this artical .

Thanks for the post im sure it will clear up a lot of confusion some ladies are having. I just want to ask what you can tell us about faulty tests? I am 99% certain i had a faulty batch of one step test strips, as a faint but clearly pink colored band appeared in the test window when i used plain tap water! (had a bfp at 7dpo and was suspicious so decided to do a control test with water). About 3-4 tests out of the batch did this. As a professional do you have any idea why this might happen?

Thanks for this post. I've gone serious rounds with folks for claiming any line at all that appears after five minutes is null and void and not to be considered no matter what. My very early bfp's, especially on ic's and cheaper store brands, have taken ten minutes or more to show if I'm still in the window of time before my missed period.

My feeling has always been that the vast majority of women who claim to get colored "evaps" are experiencing chemical pregnancies unaware. I've had two myself, one complete with a positive pregnancy test at night only to wake up to a negative test the following morning. I was told, "Oh, you got snookered by the blue dye 'false positive.'" Well, that didn't explain the nausea I'd been experiencing or the linea negra that appears on my lower abdomen almost immediately when I've conceived. But nothing would convince them that it was anything more than a blue dye false positive.

That said, I do believe in the case of legitimate faulty tests, the strips could be susceptible to "bleeding" wherein the side that should only be turning colors if it detects hcg has been poorly put together and may have been wrongly designed to react to urine (in the way of a control line). I'd hope these faulty tests are rare and would explain why women do tend to experience these in batches. Assembly line, robotic construction is more apt to make several in a row wrong if something is slightly askew and it takes even a few seconds to be caught by human operators. Such is the peril of mass production. There is simply no way to achieve 100% perfection or even for operators to catch 100% of the defective strips.

Finally, I do believe in "line eye" or wanting something so badly that you convince yourself you see it. I've seen those grey indent lines that women swear have color. I've seen stark white test strips that women swear show a line. Knowing that some early lines are difficult to photograph, I just keep my opinion to myself, but I do believe that some small percentage of what women will blame on "colored evaps" was actually never there.

And all of this confusion and heartache is part of the dark side of early detection tests. My last two pregnancies (including my current one) were completely unplanned, but I still had symptoms well before late AF that prompted me to test by the time I was only 7-10 dpo. You can see by my gallery that I wrestled with those faint lines, wondering if my eyes were playing tricks, skeptical because of all the negative hype around blue dye test, etc. But I have a two year old and an ultrasound that prove all that can be proven.