Difference between positive pregnancy test and evaporation line

Using a pregnancy test sounds simple at first: you just pee on it, wait a little while, read the results, and then Bob’s your uncle, right? Unfortunately, with evaporation lines at play, interpreting your pregnancy test results can be a little more challenging than that.

In this article:

• How Do Pregnancy Tests Work?
• What is an Evaporation Line on a Pregnancy Test?
• What Do Evaporation Lines Look Like?
• How Can I Tell the Difference Between a Faint Positive Line and an Evaporation Line?

How Do Pregnancy Tests Work?

When you become pregnant, your body goes through many changes. One of the biggest changes your body goes through in early pregnancy, is in your pregnancy hormone levels. One of these hormones, called hCG (human chorionic gonadotropin) is what is responsible for giving you a positive pregnancy test result.

Pregnancy tests work by detecting the amount of hCG in your urine- and once the hCG levels are high enough to be detected, a positive test result is shown on the pregnancy test. A positive test result can be two lines (the control line, and the test line), a cross, or even the word “Pregnant” on a digital pregnancy test.

Sometimes, the second line- indicating a positive result on a pregnancy test- can be faint; this can happen if you are still very early in your pregnancy, and your hCG levels are not very high.

If the hCG levels are not high enough, a negative test result is shown. This can look like just one line, or the words, “Not Pregnant” on a digital pregnancy test.

Sometimes, however, pregnancy tests can be negative, but still show two lines. What causes this false positive result? Often, evaporation lines are the cause. But what are they?

What is an Evaporation Line on a Pregnancy Test?

An evaporation line is a faint line on a home pregnancy test, caused by the evaporation of urine in the results window, or by the test getting wet. Evaporation lines usually develop after the recommended time-frame for reading accurate results, stated on the pregnancy test box.

Evaporation lines can appear on any pregnancy test, regardless of the brand.

The results of home pregnancy tests with an evaporation line in the results window, should be disregarded.

What Do Evaporation Lines Look Like?

Evaporation lines are usually in the place of pregnancy test lines (on the right of the control line). They are usually thin and colourless, or may even resemble a “water spot”.

How Can I tell the Difference Between a Faint Positive Line and an Evaporation Line? – 3 Differences

Evaporation lines can certainly make pregnancy test result reading much more complicated (and frustrating!). Below are 3 ways you can tell the difference between a faint positive line on a pregnancy test and an evaporation line:

1) Thickness

The first way you can tell the difference between a faint positive pregnancy test result and an evaporation line is by paying attention to the thickness of the line.

On a true positive pregnancy test result, the test line will be the same thickness as the control line. On the other hand, evaporation lines will usually be thinner than the control line.

2) Colour

The second way you can determine whether it is an evaporation line or true positive test result is by looking at the colour of the line.

Positive faint test line results are usually the same colour of the test line, or contain visible dye, even if the colour is faint. For example, on a pink dye test, the test line will be pink, even if the colour is faint. And then, on a blue dye tests, the test line will be blue in colour.

Evaporation lines contain no visible dye, and can be described as grey or colourless, with no visible dye. Evaporation lines may also be described as resembling a water spot.

3) Time Taken to Appear

The third and final way to tell the difference between a faint positive line on a pregnancy test and an evaporation line on a pregnancy test is the time taken for the result to appear.

A positive test line appears within the recommended reaction time frame – which is usually within 5 minutes, but it depends on the brands reaction time frame specification.

A evaporation line appears outside of the recommended reaction time frame- usually after 5 minutes. Any results read outside of the brand’s specified reaction time frame should be disregarded.

6 Ways to Prevent Evaporation Lines

Evaporation lines can be frustrating, thankfully, there are some steps you can take to help prevent future encounters with those pesky evaporation lines!

1. Rather than using the “Pee on a stick” (POAS) method directly, try peeing in a cup and dipping the test instead. This can help to prevent the splash-back of pee that can get the test window wet, which causes evaporation lines.
2. Make sure to check the expiration date! Using tests which have expired increase your chances of receiving false positive or false negative pregnancy test results.
3. Use digital pregnancy tests instead. Using a digital pregnancy test helps to get rid of the confusion involved with evaporation lines. After all, you can’t get much simpler than interpretting their worded results of, “pregnant” and “not pregnant”.
4. Take your pregnancy test with your first morning’s urine. With your first morning urine, your hCG levels are much higher, meaning you’re much more likely to receive an accurate result!
5. Store your at-home pregnancy test according to the storage instructions on the box ( usually between 2 and 30 degrees celcius) to avoid damaging the test.
6. Make sure you read your pregnancy test results within the specified reaction time on the box. Reading the results too soon, or too late, can risk the accuracy of your pregnancy test results.

Hi, I’m Louise- mum of one to a little boy called Mason.

I am the Digital Marketing and Admin Assistant for MyBump2Baby.

I enjoy working to provide excellent service to MyBump2Baby’s growing families.

Nice to meet you!

How fast do evaporation lines show up?

Are evaporation lines thin or thick?