Can phthalates leach faster from PET water bottles left in heat or sunlight?

What's actually in it

PET (polyethylene terephthalate) is the clear plastic used in nearly all single-use water bottles and many reusable drink bottles. PET contains chemical additives including phthalate plasticizers and antimony (a catalyst used during manufacturing). Under normal conditions, these chemicals leach into water slowly. But temperature and light change everything.

A water bottle left in a hot car can reach 60 to 70 degrees C internally. At that temperature, chemical migration accelerates dramatically.

What the research says

A 2026 study in Environ Sci Pollut Res measured phthalate migration from PET bottles under different temperature and light conditions. The researchers tested bottles at room temperature, at elevated temperatures (simulating car dashboards and sunny windowsills), and under direct UV light.

At room temperature (25 degrees C), phthalate levels were low and mostly within safety limits. At 40 degrees C (a warm room or sunny counter), levels doubled. At 60 degrees C (hot car interior), phthalate concentrations increased 5 to 10 times compared to room temperature.

UV light exposure (sunlight) independently increased migration, even without extreme heat. Bottles left on a sunny windowsill for several hours showed elevated phthalate levels.

Reusing PET bottles made things worse, as repeated filling and squeezing degraded the plastic surface and increased the rate of chemical release.

Never leave plastic water bottles in hot cars or direct sunlight. Don't reuse single-use PET bottles. Switch to glass or stainless steel water bottles for daily use, especially in warm climates.