What Is An Evaporation Line On Pregnancy Test?

A very faint line on a pregnancy test can be confusing, especially if you’re hoping you’ve conceived this month. Could it be a faint positive or an evaporation line?

Many home pregnancy tests have two lines: a control line and a test line. The control line will appear every test, even if you’re not pregnant. The test line should only appear if your urine has detectable levels of pregnancy hormone. 

When you take a pregnancy test and see two lines within the recommended time, this is a positive pregnancy test.

Most home pregnancy tests claim 99% accuracy but a study showed up to 5% of tests actually return a false negative. It’s important to always read and follow the instructions to improve the accuracy of your test. 

However two lines on a home pregnancy test doesn’t always mean you are definitely pregnant. The second, faint line could be an evaporation line. 

An evaporation line on a pregnancy test can lead you to believe it is a positive pregnancy test, leading to disappointment if further tests reveal a pregnancy hasn’t occurred. 

What is an evaporation line?

Home pregnancy tests are usually the first option for women wishing to confirm if they’re pregnant or not. 

The tests are quite simple to use. When a fertilised egg implants into the uterus, your body starts to produce a hormone called human chorionic gonadotropin (hCG). The levels of hCG are quite low in early pregnancy and increase over time. 

Home pregnancy tests have a specially treated strip within, so HCG binds to the chemical on the strip causing it to change color. 

Usually a pregnancy test involves testing your urine with a stick and checking the results window within a certain time frame.

If the results window shows only the control line, it means you’re not pregnant or the levels of hCG aren’t high enough yet to be detected. 

A control line and a test line appearing within the recommended time indicates hCG has been detected – a positive pregnancy test.

Evaporation line on pregnancy test

An evaporation line on a pregnancy test is pretty straightforward. Pregnancy test reaction time is usually between 3-5 minutes after doing the test. So you read the results in that time frame, while the test is still damp. 

When the test dries, the urine evaporates, causing the chemical strip that would show a positive result to appear slightly visible. In some cases it looks like an indentation on the test. 

Two line tests have indents where ink will pool – one for the control line and another for a test line if the result is positive. As the ink moves across the results window, it pools in one or both of the indents.

An evaporation line on a pregnancy test doesn’t occur because of ink pooling in the test line indent. 

Some women may initially see a negative result and then check the test after the recommended time. If they see a faint line they might assume the test is positive. 

Evaporation lines don’t always appear on every test. Urine varies between women and some may see an evaporation quite soon outside the recommended time to read results. Others might not see an evaporation line appear until an hour or more has passed.

The difference between an evaporation line vs faint positive?

A test line appearing in the reaction time is a positive test result. This means the pregnancy test has picked up the pregnancy hormone hCG in your urine. 

A faint test line in the reaction time is still a positive test result. Two things may have happened here:

• Your urine is diluted. Test in the morning when you first wake up as your urine will be very concentrated. 
• You have tested too early. hCG levels increase the longer you wait until after implantation. Most tests can detect low levels but when these levels are reached depends on each woman. 

If you have a faint positive test result within the reaction time, wait a few more days and repeat the test. You can read more in Faint Line On A Pregnancy Test – What Does It Mean?.

A faint test line appearing in the results window after the set reaction time is an evaporation time, not a positive test result. 

What does an evaporation line look like?

So you’ve done a pregnancy test and want to know what does an evaporation line look like? 

Evaporation lines are not faint lines reacting to hormones but faint colourless streaks of evaporated urine.

The line will often appear thinner than a true test line as well. 

What color are evaporation lines on pregnancy tests?

An evaporation line on a pregnancy test will be colourless as there is no ink pooling in the test results indent. The dye is activated by the specially treated stick reacting to the presence of hCG in your urine. 

Evaporation lines are simply evaporated urine so colorless or in certain lights may appear very faint grey. 

There can be some evaporation lines that appear to be the colour of the test dye but very light. This can be caused by a faulty test, when ink accidentally gets caught in the indent line. Once the test dries and the urine evaporates, it appears to leave a coloured line. 

This is why it’s always important to read the test in the reaction time, when the test is still damp. 

How common are evaporation tests?

Many different brands of home pregnancy tests have been on the market for years. There are so many to choose from, but there are three main types  – blue or pink dye, and digital tests. So which types are best and how common are evaporation tests?

The general consensus is pink dye tests are the better option as compared to blue dye tests they aren’t as likely to show an evaporation line. Digital tests are easier to read and won’t show an evaporation line but aren’t as sensitive as pink or blue dye tests.

Bear in mind, an evaporation line can happen if you don’t use the test correctly and read the results within the recommended time frame. 

Do evaporation lines disappear?

Most women scrutinize their pregnant tests more than once especially when trying to get pregnant. Some are worried when they see the test line fade or change after the recommended reaction time.

A positive test result can change in density over time. That’s why it’s important to only read the test results in the recommended time frame – not before or after. 

If the test line is faint or fades in that time, then doing another test in a day or so can give more accurate results. 

Do evaporation lines disappear over time? Most women say they won’t disappear but as the test doesn’t show a positive, it’s best to throw it out to avoid confusion.