Hot Drink Cup Lids May Release Cancer-Causing Chemicals

When you sip your morning coffee, you probably don’t think twice about the plastic lid—but recent tests in Taiwan found that many popular coffee shop and fast food chain cup lids may pose serious health risks when exposed to hot drinks.

Quick answer: Out of 25 tested lids in Taiwan, 19 were made from polystyrene (6 PS), and 13 of those deformed at just 90°C. At common serving temperatures (57–78°C), these lids may still break down and could release harmful chemicals. Experts warn long-term exposure could increase cancer risk.

What the Tests Found in Taiwan

In May, the Taipei City Department of Health tested plastic cup lids from 25 convenience stores and chain coffee shops—including six Starbucks locations. They found:

• 6 used polypropylene (5 PP)
• 19 used polystyrene (6 PS)

Of the 19 PS lids, 13 deformed at the standard heat resistance limit of 90°C. However, most cups were filled with coffee at 57–78°C—below the test failure point—but still enough to potentially cause deformation and chemical leaching.

Why Polystyrene Is a Concern

Polystyrene (6 PS) is a type of plastic often used for disposable coffee lids due to its low cost and decent insulation. But:

• It has a heat resistance of only 70–90°C
• It’s less durable and more prone to absorbing moisture
• When damaged by heat, it may release benzene—a known human carcinogen linked to leukemia and liver cancer

“Benzene doesn’t leave the body easily,” explained a lecturer from Hong Kong’s Institute of Vocational Education. “Wherever it accumulates, it can cause genetic mutations over time.” Taiwanese doctors also confirm benzene is a Group 1 carcinogen associated with blood and liver cancers.

What About Polypropylene (5 PP)?

The safer alternative identified by officials is polypropylene (5 PP):

• Heat resistant up to 100–140°C
• More resistant to chemicals and impact
• Used by 6 of the 19 shops that originally had PS lids

However, PP can release dioxins if burned—a separate environmental and health concern. Still, health authorities recommend switching from PS to PP wherever possible.

Current Situation in Hong Kong and Taiwan

Despite the findings:

• Taiwan has no law restricting the type of plastic used in hot drink lids
• As of the report, 7 shops in Taiwan—including Starbucks—still use PS lids
• Authorities plan to ban PS lids by the end of 2023
• In Hong Kong, no regulations exist either, and most chains use 6 PS lids

Both the Hong Kong Food and Environmental Hygiene Department and Legislative Council members have called for better oversight and testing of materials used in food service plastics.

Expert Warnings on Plastic Degradation

Medical experts warn that any plastic exposed to heat can degrade:

• “If a plastic lid changes shape or seems to melt into your drink, it’s likely releasing chemicals,” said an oncologist.
• Repeated exposure to such plastics may raise cancer risks over time

Even if a lid appears unchanged, subtle molecular breakdown can occur, especially with repeated use or high temperatures.

Frequently Asked Questions

What type of plastic is used in most coffee cup lids?

Most coffee cup lids are made from either polystyrene (6 PS) or polypropylene (5 PP). In the Taiwan tests, 19 out of 25 lids were PS, which has lower heat resistance and may degrade when exposed to typical coffee temperatures.

What is the safe temperature limit for 6 PS lids?

6 PS plastic has a heat resistance of 70–90°C. In tests, 13 of 19 PS lids deformed at 90°C. However, most coffee is served at 57–78°C, which is below the failure point but may still cause issues over time.

Are 5 PP lids safer than 6 PS?

Yes. 5 PP (polypropylene) has a higher heat tolerance of 100–140°C and is more resistant to chemicals. It’s considered a safer alternative, though it can release dioxins if incinerated.

Which coffee shops in Taiwan and Hong Kong still use 6 PS lids?

As of the report, seven shops in Taiwan—including Starbucks—still use 6 PS lids. In Hong Kong, most major chains also continue to use PS lids, as there are no current regulations against it.

Can repeated use of plastic lids increase health risks?

Yes. Experts warn that even if a lid doesn’t visibly deform, repeated exposure to heat can cause microscopic breakdown of the plastic, potentially releasing harmful chemicals into your drink over time.

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