What Is An Evaporation Line On A Pregnancy Test And Why Should You Worry About It?

If you have been trying to conceive a baby for any amount of time, you have more than likely taken a pregnancy test or two. The instructions that you receive with your tests usually have a warning on them that states that you should disregard any line that appears past the time limit. These lines are known as evaporation lines and can be a cause of irritation for those of us trying for the elusive second line. This article will help you understand why they form and what might look like an evaporation line really isn't an evaporation line at all.
by Monica Beyer

pregnancy testWhat is an evaporation line?

An evaporation line, also commonly known as an "evap line," is a term that describes any test line that appears after the time limit is up on a pregnancy test. Pregnancy tests generally have two lines on them that appear when used -- a control line that should appear every time that lets you know that the test is working as it should, and a test line that shows up only when exposed to urine that contains the pregnancy hormone hCG. The test portion of the pregnancy test contains an antibody strip that binds only to this hormone and this is what causes it to display a positive result if you are indeed pregnant.

An evaporation line is just what it sounds like -- a line caused by evaporation of your urine. Sometimes the evaporation line highlights the antibody strip and causes it to look faintly positive, and sometimes the second line looks gray or like an indentation. These results should not be considered positive even if they look like a "real" positive result an hour later.

Put the stick down!

One way to avoid evaporation lines altogether is to get rid of your pregnancy test as soon as the time limit is up. Set a timer, note the time or keep track on your watch. If there isn't a positive result, toss it in the trashcan. Better yet, throw it in the dumpster behind a restaurant, dismantle it and put as much as you can through a shredder or run over it with your car. It can be so tempting to dig the test back out and check to see if it has "turned positive" but try to resist. It's so much better for your mental health to avoid the torture!

What if it shows up in the time limit?

If an "evap line" shows up in the time limit then it probably isn't an evaporation line -- it probably is a positive result! You may feel the urge to disregard a very faint positive, especially if you've experienced evaps before, but generally tests don't turn positive within the time limit unless you are pregnant. Sometimes it can be beneficial to wait until after your period is due to take a test because as your pregnancy progresses your hCG will rise and may turn a test darker.

If you get a faint positive result (remember, a line really is a line, no matter how faint) you might take another test in two days to see if you get a more convincing result.

While false positives are rare, they do happen occasionally. If you have a faint positive result and start your period anyway you may be experiencing a very early miscarriage (and not a false positive or an evap line).

It sounds so easy, but it isn't!

While it may sound easy to wait as long as possible to take a test (and not check them out a half hour later) it can seem to be next to impossible as you get closer and closer to your test date. It really is a good idea to try to keep these things in mind -- in the end, you will be grateful that you didn't trouble yourself with questionable results!

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Ashley March 01, 2013
Hi, my name is Ashley. I recently took a couple pregnancy tests because of the symptoms that I have been experiencing. Such as sore breasts and breast size increasing I've gone from an A cup to almost a C cup. I also am experiencing changes with my nipples and my areolas are getting darker. Slight pain/discomfort in my lower abdominal area. Increased urination and hunger. Occasionally an annoying gag reflex that happens at random. And also cravings. However, I had had my monthly on Feb. 11th as scheduled. When I took the first test a faint line appeared then was gone I couldn't see it anymore. A little bit later the line had re appeared. The second test I took it showed negative then a little bit later it showed positive. What does this mean? I thought that maybe the first one had detected something. I'm really confused....
Britt October 22, 2012
Hi I was just wondering I had 3 tests in a row all on different days with a faint line in the positive spot. It's so faint you can barley see it. Then I took a clear blue digital test and it said not pregnant took one more dollar store test same think extremely I mean extremely light positive. At night I look like I'm four months pregnant and have had nipples darken. I have had pretty much every symptom in the book. My period never came this month it was light brown spotting and lasted for a few days only when going to washroom. I'm so confused on what to do any advice???
Anonymous October 18, 2012
what I don't understand is, if the line in the "determining window" only responds to the dye if there is HCG in the urine, how can the dye take to the line after the time limit? I had a faint "positive" yesterday, which I'm reconsidering as an evap, but this morning it was a big thick and blue line. how can it turn that way, after the fact, if there's no HCG in my urine?
Princess Mary May 11, 2012
hi, i am 7 days delayed already and have tested the day of missed period, day after that and 3 days after that and the last was yesterday, one in the morning and one in the afternoon. All in all 5 test all came out negative but I am feeling breast enlargement and my heart is palpitating very often. I was in a lot of stress for the past month because of my job and my older son's problem in school. Normally my period is regularly does this mean that I am pregnant?