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Evaporation Line vs Faint Positive: The Difference and How To Interpret on Pregnancy Tests

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Finding yourself in the position where you are having to take a pregnancy test can be emotional. This can be made worse if the result is difficult to read or if a test leaves you with an inconclusive result.

If you find yourself with a test that has a small streak or a greyish line where the positive line should be, this is called an evaporation line.

Let’s look at evaporation lines and faint pregnancy tests in more detail: why they occur and what they mean.

How Do Pregnancy Tests Work?

When you become pregnant your body produces a hormone called human chorionic gonadotropin or hCG.

The level of hCG in your body steadily increases as your pregnancy progresses through the first trimester. It usually doubles every 48-72 hours. At the end of the first trimester, these levels begin to drop.

Now a home pregnancy test is designed to detect hCG levels during that first trimester.  All tests work on the same principle, no matter how much they cost.

Many tests are now able to detect tiny amounts of hCG in a urine sample meaning that they can detect pregnancy and show a positive result very early on.

The levels of hCG in each woman vary and are very low around the time of a missed period. When a pregnancy test reacts with urine that contains hCG it will give a positive result. This can be a line, a dot, or even a plus sign.

There are also digital tests available that actually state in words ‘pregnant’ or ‘not pregnant.’ Most tests also have a control line that shows if the test has been carried out correctly.

If you are testing very early in pregnancy then as we have said the levels of hCG present in urine are very low and this can often lead to a very faint positive line.

But this faint line will still have some color to it which is how you can easily distinguish it from an evaporation line.

While there are tests that state they can detect pregnancy 5 or more days before a missed period the success of these tests very much depends on the level of hCG in the urine.

What Is An Evaporation Line On A Pregnancy Test?

An evaporation line appears as a slight streak where the positive line on a pregnancy test should be.

They are usually colorless and typically appear if you wait longer than the recommended time to read your result. This evaporation line can also occur if the test gets wet.

Do note that an evaporation line does not indicate that a woman is pregnant. If you do get an evaporation line on your test it would be advisable to take another test and to follow the instructions carefully.

Evaporation lines only appear on negative pregnancy tests as a positive test would change color in the same place and cover the evaporation line.

How Can I Tell The Difference Between An Evaporation Line and A Faint Positive Pregnancy Test?

There are a few different reasons that you may get an evaporation line on your pregnancy test and unfortunately, most are due to human error. 

It may be an evaporation line if:

  • More than 10 minutes have passed since the test was taken.
  • The line has no visible color in it.
  • The line is faint, colorless, and looks more like a watermark.

Remember that most tests come with a control line that will change color to show that the test has been taken correctly. If the control line does not change, this means that the test has not been carried out correctly and will need to be retaken.

A faint line on a pregnancy test may indicate a positive result if:

  • There is a visible color on the line even if it is faint.
  • The line appears within the specified time on the instructions, this is normally anything from 3-5 minutes.
  • A woman has taken an early-result test at least 11 days after she has ovulated.
  • A woman has a missed period.
  • A woman has taken a regular test at least 14 days after ovulation.

Faint Line vs. Evaporation Line

  Faint Positive Line Evaporation Line
Thickness The line will be the same thickness as the control line. It is more often than not thinner than the control line.
Time of appearance Must be within the recommended reaction time. This will vary from brand to brand but is normally 5 minutes. Anytime after the recommended reaction time has elapsed. This is normally after 5 minutes plus but varies from brand to brand.
Color Same color as the control line. Normally colorless, greyish, almost undetectable but can sometimes be light pink or light blue.

How To Prevent Evaporation Lines

Evaporation lines most often appear when the test instructions are not followed correctly.

To prevent evaporation lines:

  • Do not use a pregnancy test that is past its expiration date.
  • Do not store pregnancy tests in extreme temperatures.
  • Ensure that you check the result of the test within the recommended time frame. Evaporation lines and false positives can occur once this time has elapsed.
  • Urinate in a cup and then dip the test strip in the urine for the time specified in the instructions. This ensures that there is not too much urine splashing on the test.

HCG concentrations in urine are usually highest first thing in the morning, taking a test at this time would increase the chances of the test being positive even if you are still early in your pregnancy.

FAQs

Female hand with red fingernails holding positive pregnancy test

How common are evaporation lines?

Evaporation lines are common on pregnancy tests but they do not occur on every test.

It will depend on the chemical makeup of each individual woman’s urine. The best way to check your results are accurate is to always check them within the reaction time for the individual test.

How long do evaporation lines stay on the test?

The evaporation line will usually remain on the test for around 5 minutes. But if the stick is left out longer than that, then a faint line appears in the result area.

How faint can a pregnancy line be?

In order for a pregnancy test to turn positive, there must normally be hCG present in the urine sample. Any positive line, no matter how faint means that your test result is positive and you are pregnant.

Your levels of hCG increase as your pregnancy progresses, so if you test too early, your hCG level may still be low and you will only see a very faint positive line on the test.

The Final Thought

Waiting for a pregnancy test result can feel like those 5 minutes last a lifetime. But to ensure that there are no mistakes or doubts it is advised to take two tests.

If both show a line, even if it is a faint line, the result is more than likely positive.

If your test is positive – congratulations and now I bet you are wondering when you should see a doctor. Check out our article with all the information you need here.

If you do get a negative test and you have been actively trying to get pregnant, then why not try tracking your ovulation with an ovulation test, we have put together the 8 Best Ovulation Tests for you to check out.

Hi, I'm Emma and I'm a mother to 5 beautiful children aged from 1 to 21 years old- life is hectic! I have learned so much along the way, not only from my own children but also through my professional life. In my positions as a Childminder and Teaching Assistant, I have studied Child Development and The Early Years Developing Practice. I wish to share all of this knowledge and help you with your own parenting journey!