When it comes to growing and building full, thick lashes, serums are our go-to. But in some eye colours, they can actually cause the iris to darken.
According to Dr Rupa Wong - who wrote an article explaining why this happens - some eye colours can change with certain serums that have specific active ingredients.
She explained that the way this was discovered was pretty much by chance. It turns out that one FDA-approved medication for lengthening lashes was originally a glaucoma drop that ophthalmologists had been using for some time.
They noticed that for many patients using the medication, their eyelashes would grow super long and thick. One study looked at a specific glaucoma drop and found it caused darkening of the peripheral iris.
However, Dr Rupa noted: "This background is important to know because most of the studies done about eye colour darkening and lash serums are based on the glaucoma drop studies. Meaning, that the drop were placed INSIDE the eye, as opposed to on the lash line."
Dr Rupa went on to explain that blue eyes should not darken with lash serums, but eye colours that can change include: Green-brown; yellow-brown; blue-grey; grey-brown; hazel and green.
"The reassuring part is that there are no harmful side effects from the iris darkening. And if you have an iris freckle or mole, then that shouldn't change with your lash serum either. But, I'm pretty sure none of my green-eyed/hazel friends don't want their eye colour to darken!" Said Dr Rupa.
She also went on to list certain popular lash serum brands, pointing out the active ingredient in each.
"The plus side for these companies about not having FDA approval is the fact that they do not need to disclose the side effects. So, just because it doesn't say 'causes skin darkening' on your box... please know that it could," she added.
People were pretty shocked to hear eye colour could be changed by lash serums. Over on Twitter, one person said: "Just found out the eyelash serum has a side effect of changing your eye colour."
While another added: "One thing to note: If you have brown/golden tones in your eye, there is a risk of permanently darkening your eye colour by using lash serum.
"It sounds disconcerting, but the active ingredient in all of these can cause hyperpigmentation. And, in your eyes, that's permanent."