Can phthalates from PET water bottles increase when stored in heat?

What's actually in it

PET (polyethylene terephthalate) is the clear plastic used for most water bottles, soda bottles, and juice containers. During manufacturing, phthalate compounds can remain in the plastic as residual contaminants or processing aids. PET bottles also contain antimony, a metal catalyst used in production.

Under normal room-temperature storage, these chemicals leach slowly. But heat speeds up the process dramatically. Think of water bottles left in a hot car, stored in a sunny warehouse, or shipped in unrefrigerated trucks during summer.

What the research says

A 2025 study in J Food Sci Technol measured phthalate migration from PET bottles under different temperature conditions. The researchers stored bottled water at room temperature, warm, and hot conditions, then measured phthalate levels over time.

Higher temperatures caused dramatically more phthalate migration. Bottles stored in hot conditions released levels that could exceed safe daily intake limits for phthalates. The longer the water sat in the bottle at elevated temperatures, the worse the contamination became.

The study used probabilistic risk assessment to estimate real-world health impacts. For people who regularly drink water from bottles that have been heat-exposed, the lifetime cancer risk from phthalate exposure was above the threshold considered acceptable by regulators.

Never leave water bottles in a hot car or in direct sunlight. Store bottled water in a cool, dark place. Better yet, use a stainless steel or glass water bottle and fill it from a filtered tap.