Myth: Freezing plastic bottles can release carcinogens called dioxins into your drinks.

Reality: “We don’t believe there are any dioxins in food-grade plastics,” says Rolf Halden, Ph.D., an assistant professor of environmental health sciences at the Johns Hopkins Bloomberg School of Public Health, in Baltimore. “And even if there were, freezing wouldn’t release them — heating would.” But freezing a disposable bottle is still a bad idea. “You should use plastics only the way they were meant to be used,” says Halden. Disposable bottles are prone to breaking and are hard to clean, making them more likely to harbor bacteria. So drink up, then recycle.

Bottom Line: If you want bottles of frozen drinks, which are great on summer hikes, stick with containers that are labeled safe for reuse and freezing.