Evaporation line vs faint positive — what's the difference?
An evaporation line is a colourless or greyish mark that can appear after urine dries on a pregnancy test strip. It is not caused by pregnancy hormones — it is a physical artifact of the test drying out.
A faint positive is a real coloured line (pink or blue) that appears within the reading window because hCG was detected. Even a barely visible coloured line usually counts as positive on standard home tests.
The human eye struggles with this distinction — especially on blue-dye tests or when reading a test hours later. That's why timing, colour, and retest behaviour matter more than how dark the line looks.
How to tell evaporation lines from faint positives
Read within the window: Most tests specify reading results between 3–10 minutes. Marks that appear after this window are far more likely to be evaporation lines.
Look for colour: True positives have pink or blue dye. Evaporation lines are typically grey, white, or colourless.
Retest in 48 hours: A true positive usually darkens with first morning urine. An evaporation line will not.
Check the control line: No control line means the test is invalid — discard it and test again.
When photo analysis helps
If you're unsure whether a line has real dye colour, analysing a photo taken within the reading window is more reliable than trying to remember what you saw. ClearLine AI evaluates line colour, placement, and contrast consistently — without the lighting and angle issues that confuse the naked eye.
Frequently Asked Questions
Is an evaporation line always colourless?
Usually yes — evaporation lines are grey or colourless. On blue-dye tests, dried residue can sometimes look faintly bluish-grey, which is why blue tests are harder to read than pink dye tests.
Can a faint line still be positive?
Yes. Any line with visible pink or blue colour within the reading window is considered positive, even if it's much lighter than the control line.
What if I read the test after 10 minutes?
Results read outside the window are unreliable. If you missed the window, take a new test and photograph it within the valid time if you want an objective read.
Should I retest if I'm not sure?
Yes — retest in 48 hours with first morning urine using the same brand. A true positive typically darkens; an evaporation line will not.
This quiz is for informational purposes only and is not medical advice. It cannot replace reading your test within the manufacturer's window or consulting a healthcare provider.
