(WENY) -- Consumer craze over Stanley travel mugs has seen millions of cups sold often in a frenzy at big box retailer, but a new discovery of lead in the manufacturing process has caused some to reconsider their choice of tumbler.

The social media fueled buzz over Stanley products caused an explosion of sales for the over 100 year old company. However, some consumers are looking into the manufacturing process, which has uncovered the presence of lead in the bottles.

Whether it's in the workplace, classroom, or just out in public, you're likely to see a 40 fluid ounce quencher bottle, a product produced by Stanley. The travel mugs became an overnight sensation thanks to social media, as their insulative properties served as selling points. However Stanley recently admitted that lead, a metal toxic to developing children, is used in the manufacturing process.

"Exposure to lead can seriously harm a child's health that causes causes damage to the brain and the nervous system as well as slow growth and development, learning and behavioral problems, and hearing and speech impediments," commented Maelea VanDenBurg, Steuben County's Public Health Education Coordinator.

Stanley went from $70 million dollars in sales in 2019 to $750 million in 2023. Videos on TikTok show consumers checking for lead using at-home test kits, most of them coming up negative. Lead is used for its insulative and thermal properties, hence Stanley's reasoning behind using the heavy metal.

"And I would also suggest if it's a product like a Stanley cup or a comparable item, probably stop using that item until you know that your lead exposure has either been confirmed or denied," added VanDenBurg.

The concerns come from products that sustained damage to the protective cap located on the bottom of the bottle. We tested the interior and exterior of a bottle and thankfully no traces of lead were detected during the test. Experts and academics agree that exposure risk is low, and say an undamaged bottle remains safe unless the protective seal is removed.

Other manufacturers of stainless steel bottles like Hydro Flask and Owala have stated that they do not use lead when manufacturing products. Stanley has also stated that if the base cap falls off of a bottle, consumers are potentially eligible for a warranty.