The must-have toy for kids and teens is turning into a travel headache for some airline passengers.

Airports are warning parents to be careful when flying with kids who are carrying NeeDoh.

What is NeeDoh?

For those without kids who just HAVE TO GET every toy and gadget their friends have at school, NeeDoh toys are a line of squishy objects meant to be squeezed for fun or even relaxation. They come in a variety of colors and shapes, including cube and gumdrop variations.

The best comparison might be a stress ball, but a bit more gooey on the inside. And they're marketed more toward children than as desk toys for stressed-out office workers.

"They have a remarkable amount of therapeutic uses, even though we don't prescribe them for those uses," Paul Weingard, CEO of NeeDoh parent company Schylling, told Parade.

Can You Take NeeDoh on Airplanes?

Given the NeeDoh's tactile capabilities and potential to help relax frazzled children, it seems like the perfect thing to bring out during stressful travel days.

But some airports are saying you might want to think twice before tossing a NeeDoh toy into a carry-on bag.

"NeeDohs are considered gel and can't be carried on the airplane if not 3.4 ounces or less," Peoria International Airport in Peoria, Illinois warned passengers on Facebook this week.

The guidance follows the Transportation Security Administration's rules for carry-ons, which prohibit passengers from having liquids, aerosols and gels over 3.4 ounces.

The airport instead suggests either packing the NeeDog in a checked bag or using a fidget spinner to help satisfy antsy children when flying.

Staggering Amount of NeehDoh's Sold

NeeDoh items are being sold in several chain stores, including Target, Five Below and Barnes & Noble. But their availability can be scarce due to their rising popularity.

According to NJ.com, Amazon alone recently sold more than 100,000 NeeDoh Nice Cubes in less than a month.

READ MORE: 15 Items Amazon Absolutely Refuses to Take Back as Returns 

That type of demand will surely put the Nice Cube and other NeeDoh items among the most memorable pop culture items for kids growing up in the 2020s.

Here is a look back at what fad toys kids loved back in the 1980s and 1990s.