# What's this greasy substance that forms inside my cellphone case?

**URL:** <https://boards.straightdope.com/t/whats-this-greasy-substance-that-forms-inside-my-cellphone-case/248949>\
**Category:** Factual Questions\
**Created:** [June 6, 2004, 1:12pm UTC](https://boards.straightdope.com/t/whats-this-greasy-substance-that-forms-inside-my-cellphone-case/248949 "2004-06-06T13:12:49Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Vision\_of\_Love](https://avatars.discourse-cdn.com/v4/letter/v/5f8ce5/32.png) [@Vision\_of\_Love](https://boards.straightdope.com/u/Vision_of_Love)\
**Post date:** [June 6, 2004, 1:12pm UTC](https://boards.straightdope.com/t/whats-this-greasy-substance-that-forms-inside-my-cellphone-case/248949/1 "2004-06-06T13:12:49Z")

</div>

I have a black leather cellphone case with a clear plastic “window” on it where my phone’s screen goes. Every few days, I take out the phone from the case and I find this clear, colourless, greasy substance that forms between the clear plastic window and the screen of my phone. I didn’t get that happening with my previous cellphone and I even used the same case. This also happens to my sister’s cellphone and case.

Anyone know where this greasy stuff comes from?

---

<div class="post-metadata">

**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\
**Post date:** [June 6, 2004, 2:42pm UTC](https://boards.straightdope.com/t/whats-this-greasy-substance-that-forms-inside-my-cellphone-case/248949/2 "2004-06-06T14:42:47Z")

</div>

Probably plasticisers condensing on the case. Plasticisers are volatile compounds that are added to plastics to make them more flexible. They are typically oily compounds called [phthalates](http://www.plasticisers.org/index.asp?page=10). These can leach out of the plasticm especially in warm conditions. It’s the same phenomenon that’s responsible for the greasy layer on the inside of the windscreen of a car - the plasticisers come out of the plastic dashboard.

---

<div class="post-metadata">

**Author:** ![Vision\_of\_Love](https://avatars.discourse-cdn.com/v4/letter/v/5f8ce5/32.png) [@Vision\_of\_Love](https://boards.straightdope.com/u/Vision_of_Love)\
**Post date:** [June 9, 2004, 2:03am UTC](https://boards.straightdope.com/t/whats-this-greasy-substance-that-forms-inside-my-cellphone-case/248949/3 "2004-06-09T02:03:10Z")

</div>

I almost forgot about this thread!

Thanks for the great explanation. 🙂