We’ve all done it before. One third of women even leave their makeup on at night at least twice a week. Sometimes, washing off the makeup is just not on the list of priorities before jumping into bed and sleeping off a busy day. And I know how going to bed with a partner can be sometimes. You want to wake up looking just as good as when you went to sleep, and one fourth of women have recently admitted to wearing makeup to bed for that very reason. No harm, no foul, right?

At least that is what the Daily Mail’s Anna Pursglove thought. “How much harm can a bit of war paint really do?” she said. And with that in mind, Anna decided to conduct a month-long experiment to see exactly what sleeping with makeup on is doing to your skin’s health.

WARNING: Do NOT try this at home.

Before beginning her experiment, Anna had her skin analyzed using 3D imaging. This data would provide her with scientific results to accompany the visible changes in her skin at the end of four weeks.

Once all the data was collected, Anna powered on. For four weeks, she would apply her makeup in the morning like she would any day, but instead of washing it off at night, she would just climb into bed, mascara and all. As you can see, things did not quite go so smoothly…

What four weeks of sleeping with makeup will actually do to your skin.

Anna started realizing the side effects almost instantly. Early on in her experiment, one of her eyes had swollen shut from sleeping with mascara on. Red blotches covered her face, her lips dried out and painful cracking set in at the corners of her mouth.

When Anna went back for a 3D scan, experts estimated that her skin had biologically aged ten years in just one month. Her skin surface had worsened by 10 percent on the right side of her face and her forehead while the left side (the side Anna sleeps on) worsened by 20 percent. That’s not all. The moisture levels of Anna’s skin dropped significantly and she saw a five percent increase in the size of her pores. “This proved what my mirror reflected,” said Anna who at this point now worried if what she did was permanent. Luckily, it wasn’t anything that couldn’t be fixed by picking back up her proper skin care habits.

While leaving your makeup on a couple nights here and there will not have this dramatic of an effect on your skin, the damage is still building up. Maintaining youthful skin takes a lot of care and washing your makeup off at night can make a huge difference in the way your skin looks as you continue to age. If skin care is something that you struggle with, have a talk with your board certified plastic surgeon about possible solutions.