One would think that goes without saying, but there’s been such an epidemic of teenagers intentionally ingesting the colorful, candy-sized packs of detergent that the American Association of Poison Control Centers felt it necessary to put out an alert on the issue earlier this week: In the first 15 days of 2018 alone, poison control centers have already dealt with 39 cases. For the entirety of all of 2016 and 2017, they handled 39 and 53 cases of intentional exposure, respectively.

The spate of swallowings is connected to what’s been dubbed the Tide Pod Challenge—teens upload videos of themselves purposefully ingesting the packets of liquid detergent to social media. (YouTube said yesterday that it would start removing the videos from its platform.)

Believe it or not, this behavior is even more dangerous than you might expect. Why? There’s something about liquid laundry packs that makes them particularly toxic.

Since Procter & Gamble burst onto the scene with its Tide pods in 2012, single-serve packs have grown to nearly 17% of the laundry detergent market, according to Nielsen. And yet data suggests they are responsible for more than half of the incidents reported to poison control centers related to kids’ exposure to laundry detergent.

The outcomes are more extreme, too. Swallowing regular liquid detergent can cause a mild upset stomach. But the laundry packs can cause excessive vomiting, wheezing, and gasping—and breathing problems so severe that a ventilator is needed.

One reason for the scary outcomes is that the detergent in the packs is much more concentrated. Tide Pods, for example, are about 90% active ingredients and 10% water. But beyond that, no one fully understands why they’re more toxic.

Burlington, Vt.-based green cleaning products company Seventh Generation ran into this issue when trying to make its version of the liquid laundry packs in 2015. It thought that by using its arsenal of ingredients derived from plants—rather than the industry standard of petroleum—it could avoid the safety risks.

But Martin Wolf, the company’s director of sustainability and authenticity, wasn’t convinced. While the ingredients alone were safe, he didn’t believe there was enough evidence that the way they interacted within the water-soluble film packs would be any safer.

“We just don’t understand enough about the toxicity,” Wolf told Fortune in 2016. “We’re still trying to figure it out.”

Seventh Generation, which was acquired by Unilever in 2016, ended up launching laundry packs made with powder instead.

Procter & Gamble, meanwhile, has taken action to curb the rash of accidental ingestion. It launched educational campaigns, offers child-resistant packaging, and made the outer film of its pods stronger and bitter-tasting. The company says that as a result accidental exposures among children have decreased more than 40%.

The question now is what to do to stem purposeful ingestion. “We are deeply concerned about conversations related to intentional and improper use of liquid laundry pacs and have been working with leading social media networks to remove harmful content that is not consistent with their policies,” the company said in a statement.

For the moment, the company has launched a social media campaign and has resorted to pleading with people on Twitter media not to eat its Tide pods and to call poison control if they do.

Contact your doctor or your local poison control center. When you're feeling better, please call us at 1-800-879-8433. We're open M-F from 9-6 ET.

— Tide (@tide) January 18, 2018

Please drink a glass of water or milk and contact the Poison Control Center(800-222-1222) or a Doctor Immediately.

— Tide (@tide) January 17, 2018

Our Product is absolutely not to be consumed. Plesae, if you have, drink a glass of water or milk and contact the Poison Control Center(800-222-1222) or a Doctor Immediately.

— Tide (@tide) January 17, 2018

Contact your physician or your local poison control center. Also, call us at 1-800-879-8433 so we can find out how you're doing. Thanks!

— Tide (@tide) January 16, 2018