What are death cap mushrooms and why are they so deadly? Experts explain.

Three people have died in Australia and another person is sick after accidentally eating what appears to be death cap mushrooms at a family meal.

The meal was prepared by Erin Patterson and served to her former parents-in-law, as well as her mother-in-law's sister and husband at her home, CNN reports. Gail Patterson, 70, and her sister Heather Wilkinson, 66, died in the hospital within days of eating the meal; Gail's 70-year-old husband, Don, died a day later. Wilkinson's husband, Ian, a 68-year-old minister, is in critical condition at a hospital.

Patterson, who did not get sick from the meal, told reporters that she's "devastated" by what happened. "I loved them. And I can't believe that this has happened and I'm so sorry," she said, per CNN. While Patterson has not publicly shared what she served her guests, experts say the symptoms they experienced are consistent with death cap mushroom poisoning.

But what are death cap mushrooms and what symptoms would you experience if you ate them? Experts break it down.

What are death cap mushrooms?

Death cap mushrooms are a poisonous fungi, according to Britannica. "They are the deadliest mushrooms," Jamie Alan, associate professor of pharmacology and toxicology at Michigan State University, tells Yahoo Life. (While death cap mushrooms are considered the deadliest, other poisonous and potentially deadly fungi include Conocybe filaris, which is an "innocent-looking lawn mushroom," webcap and destroying angel mushrooms.)

"The mushrooms are the reproductive structure of a fungus that grows underground," Anne Pringle, a mycologist and expert on death cap mushrooms at the University of Wisconsin—Madison, tells Yahoo Life. "These mushrooms make a lot of different toxins."

Those toxins can't be destroyed by cooking, freezing, drying or boiling the mushrooms, she says.

The mushrooms are native to Europe, but Pringle says that "they've been introduced to other parts of the world," including California.

Your body on death cap mushrooms

Eating just a small portion of death cap mushrooms can kill you, Pringle says.

"These mushrooms contain a toxin that attacks the liver and kidneys in your body," Alan explains. "Basically, it attacks these organs to stop the normal cellular processes." Once you eat a death cap mushroom, the toxins are absorbed by the stomach and circulated in the kidneys and liver, Pringle explains. "The liver shuts down because it can't make proteins," she says. "Your liver fails."

Symptoms can be a little tricky to decipher at first. "It causes general gastrointestinal distress," Pringle says. "That's the rough thing about death cap poisoning." People may feel like "they've eaten a really bad meal — which they have," she says.

"It's often confusing to people because the symptoms are delayed," Bruce Ruck, managing director of the New Jersey poison center at Rutgers New Jersey Medical School, tells Yahoo Life. "You may not see the vomiting, diarrhea or abdominal pain for six hours after you've eaten it. In the meantime, it's actually causing destruction of your liver."

But after the initial symptoms, Pringle says, there's a "grace period" where people will feel better for a few hours before relapsing. "That's when people go to the hospital," she says.

At that point, it's likely been a while since someone ate the death cap mushrooms, and the fungi may not be viewed as a potential culprit. That makes it harder to get the proper treatment in time, Pringle says.

The takeaway

This isn't the first time someone has been poisoned by death cap mushrooms. "A lot of poisonings have the same story — people eat death cap mushrooms and they don't know what they are," Pringle says. (She notes that many of these poisonings happen as the result of foraging versus buying mushrooms at a store or farmers' market.)

"It is very difficult for a non-mushroom expert to properly identify a mushroom," Ruck says. "Many mushrooms look very, very similar. The one you pick this time may be toxic. You should not be foraging for mushrooms on your own."

Dr. Russ Kino, an emergency medicine physician and medical director of the Emergency Department at Providence Saint John's Health Center in Santa Monica, Calif., echoes that sentiment. "These things are so deadly, often there's not a lot we can do," he tells Yahoo Life. "My advice is don't eat any mushrooms, ever, at all, that are not bought at a shop. You just can't be sure."

If you suspect that you may have eaten death cap mushrooms, Pringle says, it's crucial to go to the ER ASAP. "When you get to the hospital, tell people that you've eaten a wild mushroom," she says. "If you have specimens or leftovers, take them to the hospital with you."

"There is an antidote to these mushrooms that has been FDA-approved," Alan says. It's a dye known as indocyanine green (ICG), and it can inhibit the mushroom's toxin, she says.

Time is of the essence here, though. "If symptoms progress, you may progress to organ failure, which can result in a transplant or death," Alan says.