(KTXL) — Stanley tumblers have become social-media famous in recent months and although they’ve been flying off retail shelves, news of lead being used to make them has consumers asking whether the stainless-steel cups are safe to use.

Lead is a natural metal that’s toxic to the human body. Lead is known to cause a range of health effects, from behavioral problems and learning disabilities to seizures and death, according to the United States Environmental Protection Agency.

Are Stanley cups safe to drink out of?

“Yes, Stanley uses lead in its manufacturing process for its cups, but they only pose a risk of lead exposure if the cover on the bottom of the tumbler comes off and exposes the pellet used to seal the cup’s vacuum insulation,” a Stanley spokesperson told today.com.

They said no lead is present on the surface of any Stanley product that would come into contact with beverages.

In a separate statement to FOX Business, Stanley PMI, the manufacturing company, explained how the lead is used.

“At Stanley, one of the key features of our products is our vacuum insulation technology, which provides consumers with drinkware that keeps beverages at the ideal temperature,” Stanley PMI said. “Our manufacturing process currently employs the use of an industry standard pellet to seal the vacuum insulation at the base of our products; the sealing material includes some lead. Once sealed, this area is covered with a durable stainless steel layer, making it inaccessible to consumers.”

Stanley representatives are confident that their cups don’t pose any risk as long as the lead barriers on the cups aren’t compromised.

“All Stanley items comply with Prop 65 and FDA requirements,” Stanley said on its website. “Also, all contact surfaces are guaranteed to be safe and BPA-Free. The steel we use is 18/8, or grade 304, otherwise known as food-grade stainless steel. Like all of our products, our stainless-steel items must pass rigorous health and safety tests before making them available to the public.”