Does Leaving Water Bottles in the Sun Cause Cancer?

As we step into the peak of summer, many of us carry water bottles wherever we go.

It’s a common sight to find water bottles left in cars, backyards, parks, and at times, directly under the scorching sun. But have you ever wondered about the potential health risks this could come with?

In the last few months, there has been a lot of chatter about whether leaving water bottles in the sun could contribute to an increased risk of cancer. This blog post aims to uncover the truth behind these claims.

Does Leaving Water Bottles in the Sun Cause Cancer?

So, you’ve probably heard it somewhere—maybe from a friend, a post on social media, or even an email forward—that leaving a water bottle in the sun can cause cancer.

It sounds quite alarming, no doubt. And it’s precisely because of the seriousness of this claim that we need to examine the science behind it.

The crux of this issue primarily revolves around plastic water bottles and a chemical called Bisphenol A (BPA).

BPA is often used in the manufacturing of certain plastics, including some types of water bottles. When these bottles are exposed to heat or sunlight, there’s a concern that BPA could leach into the water.

Now, why is this important?

BPA is what we call an endocrine disruptor—it can interfere with our hormones. Some research, particularly in lab animals, has linked high levels of BPA exposure to various health issues, including an increased risk of certain cancers.

But here’s the key point.

The levels of BPA that might leach from a plastic bottle left in the sun are incredibly small. Most of the research indicating potential health risks from BPA exposure involves levels significantly higher than what you’d likely get from a water bottle.

Furthermore, many water bottles sold today are advertised as “BPA-free,” so they wouldn’t have this issue.

However, this doesn’t necessarily mean it’s a great idea to regularly leave your water bottles baking in the sun.

Heat and sunlight can degrade plastics over time, which could potentially lead to other chemicals leaching into your water. It’s a good idea, in general, to store water bottles in a cool, dry place when possible.

Are there plastics with more risks to cancer than others?

When it comes to plastics, it’s not one size fits all. Different types of plastics contain different types of chemicals, and it’s worth knowing that some may carry a higher risk factor when it comes to potential carcinogens.

Based on the Resing Identification codes of plastics, there are 7 types of plastics, each with its unique use case and safety bat. You’ll usually find the Resin codes of plastics at the bottom or side, like in the image below…

Note: The way the plastics below are listed is in correspondence to their Resin Identification code. E.g. PET, the first on our list, has a Resin code of 1.

Without much ado, below they are:

1. PET or PETE (Polyethylene Terephthalate): This is a type of plastic most commonly found in single-use water bottles and various food packaging. It’s lightweight and durable, making it an excellent choice for these applications. However, PET is not intended for long-term or repeat use as it can degrade, especially when exposed to heat. There are concerns about leaching of antimony, a heavy metal used in PET production, which at high levels can cause health issues like nausea, dizziness, and even potentially more serious effects with long-term exposure.
2. HDPE (High-Density Polyethylene): HDPE is a hardy plastic frequently used for milk jugs, detergent bottles, and even some plastic bags. It’s resistant to many different solvents, and it’s considered one of the safest plastics for food storage. It has a low risk of leaching and is even used in products that require long-term storage of substances, such as water tanks.
3. PVC or V (Polyvinyl Chloride): This type of plastic is very versatile and can be rigid or flexible, depending on its formulation. It’s used in everything from food wraps to children’s toys to plumbing pipes. The concern with PVC is its potential to leach phthalates, a type of chemical used to make PVC more flexible. Phthalates are endocrine disruptors, meaning they can interfere with hormone systems, and have been linked to various health problems.
4. LDPE (Low-Density Polyethylene): LDPE is a relatively soft and flexible plastic. It’s often used for bags for bread, frozen foods, and even squeezable bottles. Although it’s not as resistant to heat as some other types of plastics, LDPE is generally considered safe and has a low risk of leaching chemicals into food or drinks.
5. PP (Polypropylene): This type of plastic is strong and heat-resistant, making it ideal for containers that need to withstand hot liquids or foods, such as ketchup bottles or yogurt tubs. PP doesn’t easily leach chemicals, even when it comes into contact with acidic or fatty foods, making it a safe choice for food storage.
6. PS (Polystyrene): Often recognized under the trademark name Styrofoam, PS is a lightweight, insulating plastic used for a variety of applications, including disposable hot drink cups, food service trays, and packing materials. The primary health concern with polystyrene is the potential leaching of styrene, especially when in contact with hot foods or drinks, as styrene is considered a possible human carcinogen.
7. Other (Miscellaneous): This category includes all other types of plastics not classified in the first six categories. It often includes polycarbonate (PC), from which BPA can potentially leach. PC has been widely used for its durability and heat resistance, found in items like baby bottles, water coolers, and the linings of most food and beverage cans. Despite the “BPA-Free” replacements becoming more common due to potential health concerns, the safety of these alternatives is still under research.

So what plastics here are the best?

Always go for #2, #4 and #5

Final Thoughts

While leaving water bottles in the sun can potentially cause certain chemicals like BPA to leach into the water, the levels are typically very small and the health risk is likely minimal.

However, to ensure you’re drinking the cleanest water possible, it’s best to keep water bottles out of direct sunlight and high temperatures, and consider using BPA-free bottles or bottles made from safer plastics such as HDPE or PP