Evaporation Lines on Pregnancy Tests: What You Need to Know

You may have heard about it before… the dreaded evaporation line or ‘evap line’ on an at-home pregnancy test. We know they don’t indicate a positive result, so why do they appear? 

In this article, we’ll cover everything you need to know about evaporation lines on pregnancy tests – including what they look like, why they happen, and how you can distinguish an evaporation line from a positive result. We’ll also share a few practical tips for ensuring your pregnancy test is as accurate as possible.   

What Is an Evaporation Line on a Pregnancy Test?

An evaporation line or ‘evap’ line on a pregnancy test is a false-positive result that can appear on traditional pregnancy tests where the test line is supposed to be. Unlike a positive test line that is in full color, an evaporation line is faint, colorless, and may even appear translucent. Evaporation lines can occur if you wait too long to interpret the results of the test. They can also occur if the test becomes wet or if it’s not taken correctly.  

How Do At-Home Pregnancy Tests Work?

At-home pregnancy tests utilize lateral flow assay technology to detect hCG (human chorionic gonadotropin) levels in urine. HCG is a type of pregnancy hormone, and it rises rapidly approximately 6-12 days after implantation. If hCG levels are above a certain threshold (usually 5-25 MIU/ml), the pregnancy test strip will display a ‘positive’ result – meaning pregnancy is likely. 

Traditional (i.e. non-digital) at-home pregnancy tests have two lines. One line is the control line, this line appears to confirm the test is working properly. The second line is the test line, which only appears when elevated levels of hCG are detected. The color of the lines can vary depending on the test. For example, control/test lines on Clearblue tests are typically blue, but it’s also common to see lines that are pink.

Digital pregnancy tests are based on the same technology, however, they contain a tiny computer that can read the results of the test strip and display the results as either ‘pregnant’ or ‘not pregnant’. This helps to avoid the confusion that can come with interpreting traditional pregnancy tests. 

In addition to at-home urine pregnancy tests, pregnancy can also be confirmed with a blood test and/or ultrasound at your doctor’s office. If you do receive a positive result from an at-home test, it’s recommended to go ahead and make an appointment with your doctor. They can confirm your pregnancy with additional testing and provide guidance on the next steps for your prenatal care. 

Why Do Evaporation Lines Appear?

Evaporation lines are most likely to appear in the following scenarios: 

• You have waited too long to interpret the test results. Pregnancy tests have a ‘reaction time’ of around five minutes after the urine sample has been taken. After this window of time, the results will appear. However, if you wait too long beyond the recommended time to check your results, there is a possibility the urine in the pregnancy test can dry up – causing an evaporation line to appear. 
• The pregnancy test becomes wet. If the pregnancy test becomes wet with water, the water can dry up or even dilute the chemicals in the test. This can cause the appearance of an evaporation line. 
• The pregnancy test is not taken correctly. If the instructions are not followed carefully, this increases the risk of receiving an evaporation line. 

It’s important to note that pregnancy test instructions can vary depending on the brand and type of test. To reduce the risk of receiving an evaporation line, always follow the instructions for each test carefully. You should also ensure your tests are stored properly when not in use and always double-check the expiration date before testing. 

Evaporation Line vs Faint Positive Result: What’s the Difference? 

Evaporation lines should not be confused with faint lines on a pregnancy test, which occur when the test line appears faded or faint in color. 

A faint test line can be a sign that you are in the very early days of pregnancy, but your hCG levels have not risen very far above the threshold of the pregnancy test. In other cases, a faint positive result may also indicate certain health concerns such as chemical pregnancy, ectopic pregnancy, miscarriage, pituitary gland tumors, and ovarian cysts. 

If you are struggling to distinguish the difference between an evaporation line and a faint positive line, consider the following: 

• Color. The main difference between an evaporation line and a faint positive line is color. An evaporation line will always be colorless, while a faint positive line will still have a hint of color.
• Timing. A faint positive result will appear within the normal amount of time when you can check your results (this will be noted in the test instructions). An evaporation line, on the other hand, will appear after the testing window. 

If you think you’ve received a faint positive result, wait a day or two and then test again. If you continue to receive faint positive results, make an appointment with your doctor. They can conduct further testing to check your health and potential pregnancy. 

How to Avoid Misinterpreting a Pregnancy Test 

Don’t Test Too Early

For the most accurate results, make sure to wait and take your pregnancy test at the right time of your cycle. Why? Because testing too early can cause faint positive and false-negative results, leading to unnecessary confusion and uncertainty. 

The standard guidance is to wait until the first day of your next missed period to take a pregnancy test. If you have a 28-day cycle, this means you can take a pregnancy test 29 days after the first day of your last period. 

You can also estimate your test day based on your day of ovulation. The standard guidance for this is to take a pregnancy test no earlier than eight to nine days past ovulation. 

If you’re not quite sure about your ovulation dates, now is the time to start tracking your menstrual cycle! The most accurate way to do this is with the Mira Monitor, which enables you to track your fertility hormones at home. When tracked over time, you can see your unique hormone curves, chart your 6-day fertile window, and predict your day of ovulation. You can also confirm that ovulation actually occurred (which is helpful for knowing when to take a pregnancy test). 

To learn more about pregnancy test timings, check out our article When to Take a Pregnancy Test Based on Science and Ovulation. 

Follow the Test Instructions Carefully

Pregnancy tests can be up to 99% accurate. However, this does rely on the user following the instructions. 

There are lots of different pregnancy tests available – from basic paper test strips to more advanced digital wands. No matter what type of pregnancy test you have purchased, always make sure to read and follow the test instructions very carefully. This will ensure that you receive the most accurate results (and reduce your chances of seeing an evaporation line).  

Read Your Results Within the Testing Window

Every pregnancy test has an estimated time when you can see your results, which is usually around five minutes after providing your sample. We know these five minutes can be excruciating – but if you get distracted and wait too long to check your results, an evaporation line may appear. An evaporation line does not confirm pregnancy. However, the appearance of a line can give you a false sense of hope that you are pregnant. 

To prevent any confusion or disappointment, make sure to read your result within the recommended time frame noted in the test’s instructions. If you need to distract yourself during this time, set a timer so that you don’t forget to check your test. 

What to Do if You See a Pregnancy Test Evaporation Line

If you’ve taken a pregnancy test and see what appears to be an evaporation line, go ahead and take another test; making sure to follow the instructions very carefully. 

If the second test still shows an evaporation line, it may be a good idea to take a digital pregnancy test. This can help take the guesswork out of interpreting your results on a traditional test. 

If you are still unsure about your pregnancy status, make an appointment with your doctor. They can take a blood test to confirm whether or not you’re pregnant. 

Final Thoughts

We know that planning a pregnancy can be a stressful and emotional process. If you need further support along your TTC journey, check out our library of free webinars, ebooks, and blogs. We’d also love to invite you to join our Facebook support group, Mira Fertility Club. 

To learn more about interpreting pregnancy tests, check out our article Decoding Pregnancy Test Results: Evaporation, Indent, and Faint Lines. 

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