When it comes to pregnancy test results, women frequently wonder what is an evaporation line (aka evap line), why it occurs and how to tell the difference between that and a faint positive. Here, we provide the answers

If you've visited the Netmums Trying To Conceive Forum to ease your anticipation whilst trying for a baby, you've probably been confronted with the question: What is an evaporation line (or evap line) on a pregnancy test?

With so much banking on those results, taking a pregnancy test can be a stressful and uncertain time. The instructions on the box might be clear enough, but when it comes to actually reading the results from a pregnancy test, it can seem more complicated than simply glancing at the little window on the stick.

Evaporation lines (evap lines), indent lines and faint results lines can throw a spanner in the works, leading to false hope, more anxiety and disappointment.

Here, we break down exactly what an evaporation line is , why it occurs and how to tell the difference between a faint positive (the desired BFP!) and an evaporation line.

• Does a faint line on a Clearblue pregnancy test mean I'm pregnant?
• Find out how early you can take a pregnancy test

How do pregnancy tests work?

To understand evap lines, you need to understand how pregnancy tests actually work.

'All pregnancy tests detect the hormone human chorionic gonadotrophin (hCG), which starts to be produced around 6 days after fertilisation,' as stated by the NHS .

Once hCG reaches a certain level in urine, the pregnancy test can measure it and give you a positive results. If there is no hCG or if it's below the measurable level, the pregnancy test is negative.

There are 3 types of home pregnancy test:

1. Mid-stream tests: You hold the test in your stream of urine for a few seconds while you're on the loo. Then you set the test aside for a few minutes and wait for the results to appear.
2. Dip tests: You use a container to collect your urine, then dip the test, which is usually a strip, into the cup.
3. Dropper tests: You collect your urine in a container, then using a dropper, drop some of the urine into a reservoir on the test.

Wondering which ones to use? Read our pregnancy test reviews

How to read the results from a home pregnancy test

Once you have waited according to the time stated in the instructions of your specific test, it should show you your results in the window.

Some test results are more clear that others. Some display 1 or 2 lines showing up in the results window. One line means the test is negative and 2 lines means you're pregnant.

The lines may be vertical and side by side or they may be crossed to look like a 'plus' symbol for a positive result.

Some pregnancy test have a mini computer inside that has a read-out that says the words 'pregnant' or 'not pregnant'.

The problem that many women are faced with, however, is that the second line can often be very faint, especially if they are taking the test quite early. Sometimes it's difficult to be sure that there's even a line there. Very stressful!

What does it mean if there is a line with no colour?

A positive pregnancy result will show 2 lines of the same colour. Sometimes the second line is fainter than the first, which can be confusing and mean different things.

For example, a faint line may mean that there is less of the pregnancy hormone being detected in your body, and therefore you'll have to wait a few days to take another test to be sure. Usually, if you're pregnant, the colour of the second line will show up more strongly in your second or third test.

However, you may be feeling even more confused if the second line on your test not only appears to be faint but also has no colour at all .

In this case, it’s possible that the second line is an indent line.

What is an indent line on a pregnancy test?

On the surface of the results strip on a pregnancy test are 2 channels where the dye can collect to show the results, so you can clearly see whether or not you're pregnant.

One of those channels is for the control line that indicates that the test is working and that the results are valid. This line is usually bright and crisp against the white background .

The other channel is where the dye collects to indicate if you are pregnant. See below for how an indent line might show up on a test.

What is an evaporation line (or evap line) on a pregnancy test?

If you see a very faint line show up on your home pregnancy test, you may be feeling a variety of mixed emotions – excited, confused, or uncertain if you've heard of the term 'evaporation line'.

According to Healthline , 'Evaporation lines are common and can occur with any pregnancy test.'

They say, 'An evaporation line is a line that appears in the results window of a pregnancy test as the urine dries. It can leave a faint, colorless line.'

Why does an evaporation line occur?

The evaporation line often appears when you wait too long to read the test.

The instructions on the box of your test will tell you how long you should wait before reading the result, and you should follow them closely to avoid reading your test incorrectly.

While you might think the results are the results, no matter when you read the test, it's actually quite important to read the results within the time recommended by the test . If you wait too long, the urine on the test can dry up completely – that's when an evaporation line can become visible where the indent line is located.

A colourless second line means that there is no dye present, and therefore what you're seeing is in fact the indent line after the urine has evaporated.

You can see the indent line because urine is made up of water, salts and other compounds, so when it dries, it can leave visible traces in the indent line.

Faint positive vs. evaporation line on a pregnancy test

If you see a faint line in your pregnancy test and it's giving you hope, you're probably going mad trying to work out whether it's a faint positive or an evaporation line.

The main difference between a faint positive and an evaporation line is that evaporation lines do not contain even the slightest hint of colour.

In fact, an evaporation line may look more like a watermark. It'll be barely visible and you might only be able to detect it when you hold the test up in the light at certain angles.

Tips on how to prevent a false positive or evaporation line

If you have an evaporation line on your pregnancy test, it's also referred to as a false positive.

We know that taking a home pregnancy test can be an emotional moment. It's easy to make mistakes, so here are tips to make it easier for you to get a result you can rely on!

• Don't test too early – It's really tempting to start taking tests before it's time, but this is a waste of time and money. It'll only add to your stress and anxiety and could increase the likelihood of you getting a false positive or even a false negative! Wait at least 2 weeks after the day of ovulation, or 1 day after the date of your expected period, before you take a pregnancy test.
• Test a few times – It's better to save your tests until your body is ready to reveal whether or not you're pregnant, and then take more than 1 test to remove any doubt you might have after you take your first one. Staggering your tests over a few days will be all the more reassuring – if you are pregnant, that positive line will get stronger with each test you take.
• Take your test first thing in the morning – Your urine is more concentrated first thing in the morning before you have eaten or had anything to drink, which could dilute it. This means the hCG levels will be easier to detect.
• Follow the instructions on the box – It might seem obvious, but it's easy in anticipation of getting the results, so many of us skip or skim over the instructions and make simple mistakes, like not keeping the test strip flat. Keep in mind that different types of tests may have different instructions, so it's important to read the box carefully!
• Set a timer – Do this to avoid reading the test too early or putting the test down, forgetting about it, waiting too long and then risking an evaporation line appearing.
• Try a different brand or type of test – Different women find different brands or types of tests easier to read. Don't be afraid to try a variety for confirmation of your results. Sometimes it's worth it for peace of mind.
• Check for early pregnancy symptoms – Look out for early pregnancy symptoms, like breast tenderness, morning sickness and missed periods, as these could be signs that you're more likely to get that BFP. ( Find out the early signs of pregnancy .)

Tempted to try alternative home DIY tests to find out if you're pregnant? Find out if the toothpaste pregnancy test really works.

What our readers say about evaporation lines on pregnancy tests

Are you struggling to understand or make out whether you're seeing an evaporation line (trust us, sooo many people experience this issue)? Here are some of the stories from women in the the Netmums Forum:

'An indent is where a line would appear if it were positive. It's literally a shallow indent in the test where the dye would sit. Evaps appear after the [period of time] that it should show a positive and they're generally grey not pink . That being said, people do occasionally get a slightly coloured evap or have a line outside of the time window that is a true positive.' – Ellie P(101)

'Hi, all! I need some advice please ... I took a preg test about 45 mins ago. My partner and I looked at it and agreed it was negative. I put it on the side and we forgot about it, then about 30 mins later my partner went to get a drink and noticed that there is a line there now in the T window. It's faint but there's a line. I don't know what to think now though because the test says do not read after 10 mins. Could this be what they call an evap line? Trying to not get excited at all. Just wondered what you all thought and needed to tell someone as I can't tell friends family lol! I am 9dpo.' – Anonymous

'I had what I think was an evaporation line on one test, as it seemed negative. Then when we tested another 5 days later, it was positive. Good luck!' – Anonymous

'Apparently if it's the one with the blue line, it could be an evap line, but if its a pink line then it's not an evap line as these are grey/blue ... if that makes sense?! I would go get a Clearblue digital that says 'pregnant' or 'not pregnant' to make sure either way.' – Anonymous

'When I found out I was pregnant, the line was really pale at first. Then a few days later (tested a fair few times just to be sure, lol), the lines were quite dark as I got more pregnancy hormones. That's with both the cheapy eBay tests and Clearblue Plus ones. I was told by the nurse that the best time to test is 1st thing in the morning, as that's when there's more pregnancy hormone in the wee.' – Anonymous

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