Why does tea make holes in plastic foam cups?

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Dear Cecil: This morning when I ordered hot tea from the restaurant next door, I got a styrofoam cup of steaming hot water and a tea bag. Soaking the bag in the water, I noticed the usual brownish white foam floating up to the top of the cup. What is this foamy stuff — preservative from the bag, or is it just happy to see me? Also, after pouring the foamy stuff out, I noticed the cup had pits and craters in it. What happened? Am I drinking melted styrofoam? Steve Holmquist, Chicago


Illustration by Slug Signorino

Cecil replies:

We’ll deal with this question in a moment, Steve. But first a word about your terminology. After this column originally appeared in the newspaper I received a friendly little note from the Dow Chemical Company informing me that while you think what you’ve got there is a styrofoam cup, it’s really a “plastic foam” cup. “Styrofoam” is a brand name applied only to Dow Chemical’s plastic foam products, none of which is cups. Clearly Dow wishes to distance itself pending the day when the melted cup scandal breaks.

Now then. Cecil always loves the thought of looming environmental disaster, so he hustled out to study this deadly phenomenon firsthand. First I got a jumbo pack of 51 foam cups, so as to do the job with the thoroughness it deserves. I also bought a lemon, a common tea additive, partly to give a splash of color to the lab (we’re into nouvelle research), but also to test the corrosive effect of the juice. I know you didn’t mention lemon in your letter, but the Teeming Millions over the years have shown a genius for omitting crucial details.

Sure enough, experiments indicated that while tea and hot water alone wouldn’t do anything, tea, hot water, and lemon — for that matter, hot water and lemon alone — caused deep cratering. In one case the pits were so deep the cup began to leak.

Convinced of the reality of the foam cup menace, I made a few inquiries. Turns out you’re not the first person to notice the effect. In 1979 a doctor named Michael Phillips wroted an alarmed letter about it to the New England Journal of Medicine. It seems polystyrene (plastic foam to you) is softened by limonene, an “acyclic terpene” that forms the principal constituent of lemon oil. Dr. Phillips cited some early research suggesting that polystyrene is — you probably saw this coming — carcinogenic.

The foam cup industry, fearing the jig was up, counterattacked. They pointed to studies by the National Cancer Institute and others indicating that polystyrene and its chemical components were harmless, at least from the standpoint of causing tumors. They even dug up tests showing lemon tea drinkers really didn’t swallow any dissolved foam — supposedly it just stuck to the side of the cup.

Suspiciously, however, nobody said anything about the “brownish white foam” you mention, leading me to think maybe the researchers weren’t patronizing the right restaurants. My advice: chuck the foam cups and stick to Mason jars. They’re fun, they’re funky, and you’ll avoid getting your tonsils lined with plastic.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.