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Evaporation Line on Pregnancy Tests: What is it?

last year10 min read
Fact checked
Last updated: Jan 23 2023

What is an evaporation line on a pregnancy test? What’s the difference between evaporation line vs faint positive? Are evap lines thick or thin? Head spinning? Read on.

Evaporation Line

This article has been reviewed by embryologist expert and educator Navya Muralidhar.

Whether you’re TTC or trying to avoid getting pregnant, pregnancy tests are some of the hardest tests you ever take in life.

Throw the evaporation line into the mix, and things get even trickier.











So what does an evaporation line look like? What causes it? And what should you do if you think you’ve got one?

Let’s take a look.

In this article: 📝

  • Evaporation lines and pregnancy tests
  • What are evaporation lines?
  • How do you know it its an evaporation line?
  • How can you tell if an evaporation line is positive?
  • How soon do evaporation lines appear?
  • Should I trust a faint positive pregnancy test?
  • How common is an evaporation line?

Evaporation lines and pregnancy tests

First, a quick spin around how home pregnancy tests work.

Basically, they’re on the hunt for a hormone called hCG that’s released when implantation happens.

If your test is able to find a sufficient amount of hCG in your pee, you get a positive result.

If not, you get a negative result.

We’re sure you have a solid idea of the steps involved for all this detective work to take place but we like to cover all our bases.

Home pregnancy tests require you to pee on the test itself or, better yet, you can pee into a cup and either use a dropper to get the liquid onto the test or dip your test into the cup.

All pretty straightforward.

And then come the results.

How these show up depends on the display setup of the pregnancy test you’re using.

The more old-school tests show one line if you’re negative and two if you’re positive.

Digital pregnancy tests swap simple lines for an ultra-modern display screen that show the words PREGNANT or NOT PREGNANT – taking away at least some of the guesswork.

If you’re using the version that shows one line for negative and two for positive, there’s a chance you could get an evaporation line which can confuse your results.

Which brings us to the evaporation line.

What are evaporation lines?

An evaporation line (or evap line) on a pregnancy test can look like a very faint, discolored positive result – but actually isn’t one.

The line appears only after your pee has evaporated (hence the name) and may mean that too much time has passed between taking the test and checking your result.

Hey, it happens to the best of us!

But a time-lapse isn’t the only reason for the appearance of the evap line.

It could be that the test got wet.

Or that it just happened.

(Read: don’t blame yourself. Breathe. This is stressful enough.)

How do you know it its an evaporation line?

So what do evap lines look like?

Well, unfortunately, evaporation lines can look a little like faint positive lines, which can lead to some disappointment later on.

But for the part, you can think of them as more streaks than strict lines.

This means an evap line may not run across the test.

Are evaporation lines thin or thick?

Generally, most evaporation lines tend to be thinner than positive lines.

So positive lines are also usually a little thicker than an evap line.

But if you have no reference to compare it to, it’s easy to misread.

What color are evaporation lines on pregnancy tests?

Wait, so do evap lines have color?

In the great evaporation line vs faint positive debate, how do you tell which is which?

The key difference is that an evaporation line is colorless (which may appear as a faded gray on most tests).

This is an important distinction because if your test is positive, the line that tells you it’s a positive result will appear in the same spot as the evap line – but will have some color to it.

(BTW, if you need help, there’s a whole Peanut community dedicated to this very topic)

So if you’re looking at an evaporation line with blue dye or a pink evaporation line, chances are, you’re looking at a BFP ‒ a big fat positive!

That being said, pregnancy tests that use blue dye can be harder to read, since gray evaporation lines can look blue.

[False positive](https://www.peanut-app.io/blog/false-positive-pregnancy-test0 blue dye evap lines are very much a thing.

So much so, that most healthcare professionals would recommend a pink dye test over a blue everytime.

The key way to tell the difference between an evaporation line vs blue dye positive lines is to see whether the line gets thinner.

If it stays thick, it’s more likely to be positive, but if it gets thinner, you could be looking at an evap line.

How can you tell if an evaporation line is positive?

So in the battle of evaporation line vs faint positive, how do you tell the difference?

Here’s our checklist of evap line vs faint positive – run through these and you should have your answer:

  • How long has it been since you took your pregnancy test? If less than 10 minutes, it could be positive, if 10 minutes or more, it could be an evap line.
  • What color is the line? If it’s pink or blue, it could be positive. If it’s gray and colorless, it could be an evaporation line (beware the false positive blue dye evap lines).
  • How thick is the line? If it’s thick and clear, it could be positive. If it’s thin (or getting thinner), it could be an evap line.
  • Have you missed your period? If yes, it could be positive. If no, it could be an evaporation line.
  • Have you waited two weeks after ovulation to take your test? If yes, it could be positive. If no, it could be an evaporation line.
  • Has the control line on the test changed color? If yes, it could be positive. If no, it could be an evap line and you may have taken the test incorrectly, so it’s worth trying again and double-checking the instructions.
  • Is the pregnancy test in date? It’s very rare to have a false positive, even on an expired pregnancy test, but it can happen.

Can a pregnancy test turn positive if it sits too long?

Looking at some possible false positive blue dye evap lines?

It might be that your pregnancy test has sat for too long and now shows an evaporation line.

As blue-dye pregnancy tests can make gray evap lines look blue, it can be hard to read them, especially after 10 minutes have passed.

Usually, you’ll have an accurate result in the first 2-4 minutes of doing the test.

If you’re not sure, take a photo in good lighting and get some opinions ‒ our TTC community of Peanut is great at deciphering pregnancy tests!

How faint can a pregnancy line be?

Struggling to tell the difference between evap line vs faint positive?

Well, positive lines can be pretty faint, especially if it’s very early in your pregnancy.

Pregnancy tests detect hCG levels in your pee, which increase from the first week of pregnancy.

So a faint positive line could mean you are pregnant, but you’re very early, as your hCG levels are low.

If you’re not sure whether it’s a faint positive or evaporation lines on pregnancy tests, try waiting another week (we know, it’s hard to wait) and take another test.

Do evaporation lines get darker the longer it sits?

Not usually, no. If your line is getting darker, it’s more likely to be either the control line (this is generally the darkest line on a pregnancy test) or a positive result.

Evaporation lines on pregnancy tests usually get lighter as your pee evaporates.

How soon do evaporation lines appear?

Evaporation lines tend to appear after about 6 minutes of taking a pregnancy test.

But if you’re reading your test after 10 minutes, a gray line is likely to be an evaporation line rather than a positive.

Positive lines can appear within about 2 minutes, but if you see a line appear after 10 minutes, it’s not likely to be positive.

How long does an evaporation line last?

Evap lines usually only develop after the window of time for reading the results—and won’t appear every time you take a test.

One way to decrease the chances of the kind of confusion evap lines can cause is to read your results in the time that it states in the instructions.

Sometimes this is two minutes, sometimes it’s up to 10.

While evap lines do fade a little, thinning as time passes, they don’t tend to fully disappear.

Once the pregnancy test is discolored from an evaporation line, it’s not possible to change it back to new.

Should I trust a faint positive pregnancy test?

Yes, if you see a faint positive line, it has color and you’ve checked the test within 10 minutes, it’s likely to be positive.

Faint positive lines usually mean that it’s very early in your pregnancy, as your hCG levels are still low, but growing.

There are even stories from our Peanut mamas where the evap line turned out to be positive – although these are usually because the faint positive line was hard to read.

Sometimes, it can also be too early in a pregnancy to show a positive result, so seeing a negative result or an evaporation line can result in a pregnancy.

Our advice is to wait 2 weeks after ovulation to take your pregnancy test, take it first thing in the morning, and read it within 10 minutes.

How common is an evaporation line?

Evap lines are common and can be both disheartening and confusing.

If you’re at all uncertain about your result, take another test.

So that you can get as accurate a result as possible, it’s best to wait until after your next expected period, or two weeks after ovulation.

This will allow your hCG levels to get above 25 mIU/mL, the levels necessary for a positive result.

False-positive pregnancy test results are also possible for several reasons, one of which is a very early pregnancy loss.

If you’ve just been pregnant or are taking fertility meds, you might also get a false positive.

Do all pregnancy tests have evaporation lines?

No. While evaporation lines on pregnancy tests are common, they don’t appear on every test.

Some pregnancy tests are electronic, showing either PREGNANT or NOT PREGNANT.

It also depends on the brand of pregnancy test as to how hard it can be to tell the difference between a faint positive and an evap line.

For example, the evaporation line on Clearblue pregnancy tests can be easy to misread as a faint positive, since the gray color can look a little blue - especially when you have line eyes from trying to read a faint line.

However, a First Response evaporation line may be easier to spot, since the positive line is a pink color, so easier to tell the difference between a gray evap line and a pink positive line.

If you’re unsure about whether you see an evap line or a faint positive, try waiting another week to take another test.

If you need help, reach out to your healthcare provider or even our Peanut community – our TTC groups can be amazing at interpreting pregnancy test results.

This journey can be pretty confusing, especially when you throw evaporation lines on pregnancy tests into the mix.

It’s more than okay to ask for support.

We’re here for you.

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