Do plastic water bottles left in a hot car release more chemicals?

What's actually in it

Heat accelerates the breakdown of plastic. A plastic water bottle sitting in a car on a summer day can reach temperatures of 65-80C (150-176F). At those temperatures, PET plastic degrades faster, releasing more microplastic particles and leaching more chemical additives into the water.

The combination of heat and mechanical stress (squeezing the bottle, drinking from it at different levels) creates multiple pathways for plastic contamination into the water you drink.

What the research says

A 2025 study in J Hazard Mater measured microplastic release from bottled water under in-vehicle conditions using carbon nanotube fluorescence detection. They found dramatically increased microplastic particle counts in water from bottles that had been left in a hot vehicle compared to bottles stored at room temperature. The particles were small enough to absorb through the gut.

Never drink water from a plastic bottle that's been sitting in a hot car. Dump it and refill. Better yet, stop using single-use plastic bottles altogether.

Stainless steel alternatives for water bottles stay cool longer, don't shed plastic particles, and don't change the taste of water even in hot conditions.