How Apple makes sure the Apple Watch doesn't harm your skin

An unusual video published by Apple on Thursday looks into a funny practice at Apple: it makes fake human sweat so it can test its products in real-world conditions, like when things get a little icky.

"We use fake human sweat," Art Fong, green chemistry program manager at Apple, says in the video. "We want to mimic actual use conditions, but we're not going to go around collecting sweat from human employees."

So by testing products like Apple Watch bands in this fake sweat, Apple can ensure that they won't cause a negative reaction either from humans or the environment.

Previously, users who have worn fitness trackers and smartwatches made by Fitbit and Jawbone have said that their wristbands have given them rashes.

When the Apple Watch first came out, there were some scattered reports that it could irritate skin, too, but anything worn closely to the body for long periods of time can cause irritation.

This clip is one of four new videos Apple released to commemorate Earth Day. All four were illustrated by James Blagden, who is best known for his fantastic video called "Dock Ellis & the LSD No-No."