(CNN) — Outraged parents are taking to social media after finding mold in their children’s sippy cups.

After breaking open the white spout on the underside of the lid of Tommee Tippee sippy cups, parents are finding black mold inside.

Laura Greene, a mom from Forsyth, Missouri, found mold in her 19-month-old daughter’s cup on Friday after seeing several other parents posting about it on Facebook. Greene said she has been using the cups for about a year, putting cold milk and water in them for her daughter.

“We spent 15 minutes sawing the spout open. Once we got inside, it was covered in black mold.”

Greene said she always washed the cup immediately after each use. She washed the cup by hand with hot soapy water or in the dishwasher with all pieces removed and washed separately.

Greene was upset to discover the mold in her daughter’s cup and posted to the Tomee Tippee North America Facebook page with photos.

We have many sippy cups and I take them apart and clean them after each use however the way these cups have been made it…Posted by Stephanie Phelps on Wednesday, February 24, 2016

“I can’t imagine how long she’s been drinking mold,” Greene wrote. “It makes me feel sick just thinking about it.”

Some parents are claiming the moldy cups made their children sick. Amanda Townshend, a mom from Lacey, Washington, discovered mold in her son’s cup on Wednesday. She said it took her 30 minutes using a screwdriver and hammer to break it open.

Townshend’s son is 16 months old and has been using Tommee Tippee cups for about 10 months. She told CNN that her son always had a stuffy nose after using the cups.

“We didn’t put two and two together of the sippy cups and his health until recently,” Townshend said. “He’s always had a stuffy nose after using them and just about a week or so ago he had an upper respiratory infection.”

Just found CHUNKS of mold in our sippy cups! Very disgusting and this isn’t even a sippy that’s been used a lot. We have…Posted by Amanda Townshend on Wednesday, February 24, 2016

Townshend took her son to the doctor Wednesday to ask if the mold from the sippy cup could have caused the infection. She said the doctor told her it was possible, but it’s hard to tell for certain.

Mold usually does not cause any symptoms, said Dr. Jennifer Shu, pediatrician and co-author of “Heading Home with Your Newborn.”

“Individuals who are sensitive or allergic to mold may experience nasal congestion or wheezing,” she said. “In general, mold creates more of an ‘ick’ factor than actual illness.”

Tommee Tippee issued a statement apologizing to customers who had problems cleaning the valve.

Thank you for your patience with us. First we’d like to assure you that child health and wellbeing is at the heart of…Posted by Tommee Tippee North America on Thursday, February 25, 2016

“Child health and well-being is at the heart of everything we do, and we’re taking the current concerns around our Sippee cups very seriously,” Tommee Tippee said.

Tommee Tippee said it will be launching a new cup in the next few months. In the meantime, the company is offering customers a see-through valve that will enable parents to ensure the valve is clean.

“We want everyone to be happy with our products and we always want to exceed expectations,” a spokesperson for Tommee Tippee said.