After getting a negative result on a home pregnancy test, it's fair to conclude that you're not pregnant. However, if you happen to glance back at the test later in the day, you may be surprised to see that a positive line has magically appeared. There are a few reasons why this can happen. However, in most cases, the originally reading of the test, "not pregnant," is typically the correct one.
What Are Evaporation Lines on a Pregnancy Test?
The instructions on most pregnancy tests will advise you to read the results within a certain window of time. This usually ranges between a couple of minutes up until 10 minutes later. If you see a positive result beyond this time frame, you may be left second-guessing the results.
However, the false-positive reading, in this case, is due to something called an evaporation line. Evaporation lines are not indicative of a true positive result.
Evaporation lines happen when the urine that was on the test area starts to dry. The chemical composition of the urine sample changes due to evaporation. As a result, the test may start to display a positive line. After the allotted time has passed, you should discard the pregnancy test to avoid confusion.
If you follow all of the instructions correctly, you may notice a thin, faint test line that appears within a few minutes. It can seem at first that the line is too faint to count, but after 10 minutes, it darkens. There are several possible explanations for this line:
- Chemical pregnancy: When implantation of a fertilized egg happens, hCG is produced, even though that egg may not be viable. Chemical pregnancies are the most common cause of early miscarriage. Without taking a pregnancy test, the miscarriage may easily be mistaken for a regular period.
- Lower sensitivity test:You might need a test with higher sensitivity levels so that you can get accurate results earlier in the pregnancy. Look for "early results" indicated on the test label.
- Too early in your cycle: If you test earlier than 10 to 12 days past ovulation, the hCG hormone may not be high enough to produce more than a very faint line. The best time to test is after your period is late, or 2 weeks after you ovulated.
- Too much fluid: You can dilute your urine sample if you are urinating too frequently or drinking too many liquids—this is why first-morning urine samples are recommended for pregnancy testing.
False Negative Results
While true false negative results are rare, there are multiple reasons why you could get a negative or faint result even if you are actually pregnant, such as not waiting long enough into your cycle to test or testing with diluted urine. Always use a sample from your first-morning urine (which is more likely to have higher concentrations of the pregnancy hormone, hCG).
If you are still unsure about pregnancy test results, wait a few days and test again. If you have any questions or concerns about whether or not you could be pregnant, consult with an OB/GYN.
A Word From Verywell
It can very stressful to see conflicting results on a pregnancy test, such as faint lines or evaporation lines. If you're unsure about your results, retest in a couple of days or talk to your doctor about a follow-up blood test for confirmation. Following the directions on your pregnancy test helps avoid the confusion or disappointment of a false positive.
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
By Robin Elise Weiss, PhD,
MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.
Thanks for your feedback!
Are you having a hard time telling if your test result is a faint positive or evaporation line? Here’s how to figure it out.
By OBGYN Dr. Kenosha GleatonPeeing on a stick (affectionately known as POAS) can bring a lot of emotions and sometimes confusion. Home pregnancy tests might be convenient, but they may also leave you with questions: Is it a false positive or negative? Why do I see faint lines? If you get a faint line, how do you know if that's a positive result or an evaporation line? This guide will walk through how to tell the difference and how to avoid getting evaporation lines.
What is an evaporation line on a pregnancy test?
An evaporation line on a pregnancy test is a faint line (or rather, mark) caused by a test reaction that occurs when the urine evaporates, or when the test gets wet. Sometimes this line appears in the test window, making it look like a faint positive result.
Evaporation lines are colorless streaks, not actual lines. They typically appear if a person waits for longer than the suggested time to read the test result. An evaporation line can also appear if the test gets wet.
What color are evaporation lines on pregnancy tests? What does an evaporation line look like?
Evaporation lines are actually streaks and not faint lines. They are called "squinters," meaning you have to look closely to see them. Often, these lines will not go entirely across the test. Depending on the type of test, the evaporation line may look more gray than pink. Yet, a faint positive line can be mistaken for an evaporation line on a home test. If an evaporation line appears, it is best to take another test for an accurate result.
What can cause a faint positive line?
Before discussing the difference between a faint positive line and an evaporation line on a pregnancy test result, it helps to know what can cause a faint positive. A faint positive line can simply mean that the levels of hCG hormone, often referred to as the pregnancy hormone because it is one of the first signs of pregnancy, are low. So, if you see a faint line on your home pregnancy test, this simply means that the hCG hormone level in your urine is low, and you want to try again in the morning when it's more concentrated or levels have risen.
How can I tell the difference between a positive result and an evaporation line?
So, you're trying to read a pregnancy test result and there's a faint line, how can you distinguish between the two? There are two ways to tell the difference between a positive result and an evaporation line:
- Is it a pink line? If the result shows a pink test line that looks similar to the pink control line, then it’s likely a positive result. A positive result will run from the top of the test window to the bottom with the same thickness as the control line (even if it’s more faint). Is it a greyish white squinter that doesn’t look like the control line? Then it’s probably an evaporation line.
- When did the line show up? If a pink line showed up quickly, then it is likely a positive, pregnant result. If the line only showed up much later (say ten minutes or more) than the control line, it may be an evaporation line.
The best way to know for sure is to take another test. We suggest waiting a day, since the level of hCG (the pregnancy hormone) in your urine typically doubles in a matter of days. If the line on your test tomorrow becomes darker and more clear, then you can be confident it's a positive pregnancy test and not an evaporation line.
How to prevent evaporation lines
Usually evaporation lines appear if you haven’t followed the instructions on the test’s packaging. But if you continue to get evaporation lines, we suggest:
- Try peeing in a cup and dipping the test in the cup (instead of peeing directly on the test). This prevents splashing of urine that can make a test invalid.
- Try testing first thing in the morning (when your urine has a higher concentration of hCG hormone).
- Only use tests before the expiration date on the wrapper.
- Don’t open the wrapper until you’re ready to start testing, and don’t use it if the wrapper is damaged or torn.
- Store your pregnancy tests between 36-86°F (2-30°C).
- Wait five minutes to look at your results—and make sure to read the results within 15 minutes.
What pregnancy tests are best for avoiding evaporation lines?
Make sure to find a pregnancy test that uses pink dye. That's because blue dye tests are notorious for leaving evaporation lines. The Natalist Pregnancy Test is easy to use, with pink dye that makes the answer as clear as possible.
Takeaways
- Evaporation lines do occasionally happen when the urine evaporates.
- The best way to tell is by reading the results within the timeframe explained in the instructions.
- A positive result will have a test line that runs from the top of the test window to the bottom with the same thickness and color as the control line.
- An evaporation line will be a grayish white mark that appears after ten minutes.
- The best way to know if you are pregnant is to test again tomorrow.
We’re believing in a positive test and outcome for you!
Featured Image by Edgar Hernandez