What 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!