Is a water bottle left in a hot car dangerous?

This page is for anyone who has seen the warning that water bottles left in a hot car can cause cancer. It explains what the FDA (U.S. Food and Drug Administration) says about the chemical usually blamed.

Someone forwards it every summer. A bottle of water sits on a car seat. The sun beats through the windshield. The claim is that heat drives cancer-causing chemicals out of the plastic and into the water.

The chemical usually named is BPA (bisphenol A), which is used in some plastics and can linings. The FDA page on BPA is a good place to start, instead of arguing with the email.

FDA reviewed BPA in food contact uses. Its conclusion is clear. BPA is safe at the current levels occurring in foods.

That was not a quick opinion. In the fall of 2014, agency experts completed a four-year review of more than 300 scientific studies, covering work published or available from November 2009 to July 2013. The review found no information that called for a revision of FDA's safety assessment at that time.

One fact helps here, though the chain email treats it as a scandal. Packaging is not perfectly sealed at the molecular level. FDA accepts that small, measurable amounts of BPA may move from packaging into food during normal use.

The regulatory question was never "does anything move across." It is "how much, and is that amount safe." FDA's premarket review of food packaging assesses the likely migration from the material, to assure that any migration to food occurs at safe levels.

Detecting a substance is not the same as being harmed by it. And detection technology has become extremely good.

The most interesting part of FDA's page is about the body, not the bottle. FDA-supported studies found that the body quickly breaks BPA down into an inactive form after it is swallowed. Research indicates internal exposure to the active form is predicted to be below 1 percent or less of the total BPA level administered.

So even the amount that reaches you is mostly turned into something that does not act like BPA. That one biological step does much of the work behind the safety conclusion.

That page is about BPA and food contact uses. It does not look at hot car temperatures, sun exposure, or how long a bottle sat on a seat. Someone may claim FDA studied bottles in cars. They are describing a document that this page is not.

Here is the fair way to state it. FDA has assessed the chemical at the center of the rumor, and judged it safe at the levels occurring in foods. The specific hot-car story has not been assessed separately on that page.

Nothing here asks you to change what you drink from. Maybe plastics still nag at you. Then here is the honest framing. FDA has looked hard at BPA and stated a conclusion. FDA says most swallowed BPA is converted to an inactive form. And the hot-car story is a layer added on top.

Forwarded health warnings arrive with urgency and no source. Checking the agency's own page takes a few minutes, as we just did. It usually settles the matter.