For months, American Airlines flight attendants have claimed their new uniforms are causing itchy rashes and hives, while the airline and the maker of the uniform have denied any problem with the apparel. Which raises the question: If it’s not the uniforms, then what is making the flight attendants sick?

The Association of Professional Flight Attendants has been going back and forth with American Airlines and Twin Hill, the manufacturer of the garments, but even with $1 million worth of toxicological testing thrown at the problem, the culprit has yet to be found, reports Bloomberg.

And things are getting bad, the union says, with about 10%, or 2,300 of the flight attendants it represents, reporting adverse reactions like skin rashes, sore throats, fatigue, and vertigo, since they started wearing the new uniforms.

“I’m very confident that there’s something in that fabric that’s causing this,” said Bob Ross, the union’s national president. “Some [people] react right away. Lots of other people are feeling the effects just by being around the uniforms.”

He says he wore the new uniform’s cotton shirt, “and by the end of the day my entire chest, neck, and arms were red.” He had to take two showers and dispose of both the shirt and the packaging it came in.

A flight attendant also told Bloomberg that she’s been to the doctor 12 times for tests and consultations after she says her throat grew hoarse and she broke out in hives after wearing the uniform.

But both American and Twin Hill say they’ve done testing and have not found any substances that shouldn’t be in the clothes, or any chemicals in unsafe levels. The union says it’s spent $20,000 on its own testing so far and wants American to reimburse it. American even went so far as having some executives wear the controversial uniforms to work to show how safe they are.

Things reached tense levels last week as well, when Twin Hill accused APFA of canceling appointments to test uniform pieces in person at its factory in Houston. APFA says it wouldn’t make sense to test pieces from that facility, as they could’ve been created somewhere other than where the problems originated.

Now, the union wants to look at how dozens of chemicals used in the uniform interact, as well as the packaging they come in.

“Say there’s five different chemicals they test, and they all stay within limits—synergistically, how do they interact?” Ross asked.

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