Pregnancy tests seem pretty straightforward: pee on a stick, wait a few minutes, and look for two lines.
But what if there’s a faint, colorless line on your test? Are you pregnant? Let’s answer the question, what is an evaporation line on a pregnancy test?
Pregnancy tests are one of the most common home health tests, and they’ve improved a lot over the years. It’s now possible to detect a pregnancy earlier than ever, 4 days before a missed period. But it’s still possible for home tests to give confusing results.
Let’s talk about what the lines on a pregnancy test are. First, you’ll have a control line. This line should show up whether you’re pregnant or not, and it’s used to ensure that the test is working. It should be dark, which helps you assess the other line that may or may not show up.
The second line on a pregnancy test is the one that will tell you your test result. If it’s dark or faintly positive, you may be pregnant. If there is no line, you’re probably not pregnant.
Pregnancy tests look for a hormone called human chorionic gonadotropin (hCG) in urine.
In early pregnancy, hCG rises to support the growth of the implanted egg. Once a pregnancy test picks up on hCG, even in small amounts, the second line appears.
But what if you get a faint line that doesn’t look like a positive? What if your test is negative, then a line appears later on?
Evaporation lines are colorless marks that can look like a faint positive on a pregnancy test. Let’s talk about what evaporation lines are and why they happen.
Evaporation lines, sometimes called EVAP lines, are faint remnants of evaporated urine on a pregnancy test.
These often happen when a negative test has been sitting out for a while, long enough for liquid to evaporate off of it. When the liquid disappears, the salts in the urine remain on the test. These salts may create what looks like a faint line.
When using a pregnancy test, be sure to look at the instructions. Many tests have different read times. After you’ve dipped your strip, or peed on it, you’ll need to wait a specific amount of time to read the results. But if you wait too long, your results may be invalid. If you notice any evaporation lines on your test, you’ve probably waited too long to read it.
An evaporation line will not tell you if you are pregnant or not. The best thing to do if you notice an evaporation line is to throw your test out and take a new one.
Evaporation lines are colorless marks that may show up in place of the second line on your test. They’re very light, and you’ll notice that they’re not nearly as defined as your control line. They may look like wet spots, like when you spill water on a white tablecloth.
You may notice an evaporation line gets lighter with time. This happens as more liquid evaporates from the test strip. But generally, evaporation lines don’t fully go away.
If you’re waiting for an evaporation line to disappear, you’re better off throwing that test away and getting a new one. An evaporation line is an invalid result, and won’t tell you if you’re pregnant or not.
A faint line happens when there’s enough hCG in your urine to trigger the test, but not enough to cause a dark line. This is still considered a positive result, and can happen for a few reasons.
It may be that your fertilized egg only implanted a few days ago. It takes several days for hCG to rise after implantation so that a pregnancy test can pick it up. In the first few days of pregnancy, hCG rises steadily every day. Try taking another test the next day, you may have a darker test line.
Faint lines can also happen if your urine is diluted. This can happen if you’re been drinking a lot of water to get ready for your pregnancy test. More water in your urine means that hCG will be present in smaller amounts, causing a lighter test strip. One way to avoid this is to take your pregnancy test in the morning, when your urine is concentrated.
In rare cases, a faint line may be a sign that hCG is present when it shouldn’t be. This can also happen with a normal positive line. “Phantom hCG” is when a woman isn’t pregnant but has low levels of hCG in her urine or blood. However, this is a rare occurrence. If you’ve taken a pregnancy test for several days and gotten the same faint line result, see your doctor for clarification
How can you know if you’re looking at an EVAP line or a positive line? Take a look at this chart comparing faint positive lines with evaporation lines:
If your negative pregnancy test turned positive after several hours, it’s still a negative result. The first result you read is the most accurate one.
One important thing to know about pregnancy tests is that their results are only valid for a little while. After reading your result, you don’t need to keep your test and wait for it to change. Keeping your negative pregnancy test out runs the risk of causing an evaporation line, which can look like a faint positive.
This is most likely still a negative result. 10 minutes may not seem like a long time, but it’s enough for an evaporation line to appear. This line may look like a positive result, but it’s not. If you still think you may be pregnant, throw out this test and use a new one.