Poison Hemlock—Here's What to Know About This 'Deadly' Plant

It doesn't usually cause a rash, but you should still steer clear of this weed.

Poison hemlock has a pretty scary reputation for being toxic. And it's understandable that you might be a little—or a lot—nervous about coming into contact with it.

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But being aware that you should avoid poison hemlock and actually knowing what the toxic plant looks like are two totally different things. Here's what you need to know, plus whether its rep as being the "deadliest plant in America" is actually legit.

What Is Poison Hemlock?

Poison hemlock is a toxic plant, and all parts of the plant—the leaves, stem, fruit, and root—are poisonous, according to the United States Department of Agriculture (USDA).

Poison hemlock has white flowers that grow in small clusters, and each flower eventually develops into a green, deeply ridged fruit that contains seeds. After the fruit ripens and matures, it turns a grayish brown color. Poison hemlock has a hollow stem with small purple spots, delicate leaves like parsley, and a white root (it's in the same family as parsnips and wild carrots).

Poison hemlock is in almost every state in the US, and per the USDA, it tends to grow along fence lines, in irrigation ditches, and in other moist places. It can also get up to three meters tall.

Is Poison Hemlock Actually Poisonous to Humans?

Unfortunately, yes. The plant has a few toxic compounds, including coniine, g-coniceine, and piperidine alkaloids, per the USDA.

The biggest issue with poison hemlock is people accidentally eating it, Sarah Shafer, MD, assistant professor of emergency medicine at Baylor College of Medicine, told Health. "People get poisoned because they mistake it for a wild parsley or wild carrots," Dr. Shafer said.

Some people may even "pick it out of their garden and put it in a salad," thinking that it was something they had grown, Dr. Shafer said. Sound terrifying? Yep. "It's scary," Dr. Schafer said.

Children have also died after making whistles from hollow stems of poison hemlock, according to the USDA.

People generally assume that you'll get a rash or blisters from handling poison hemlock, but that's (mostly) a myth, said Jason Rizzo, MD, a dermatologist at Western New York Dermatology in Williamsville, New York. "It's a common misconception that poison hemlock sap will cause rashes and blisters," Dr. Rizzo said. "It's not like poison ivy, poison sumac, or poison oak."

There is a caveat, though: If you have a cut or happen to expose one of your mucus membranes (like your eyes or nose) to poison hemlock, the toxins in the plant could get into your bloodstream and make you sick, Dr. Rizzo said. (King County, Washington, health officials specifically warned of a case of one woman who had a "severe reaction" to poison hemlock after pulling plants on a hot day.)

Signs You've Come Into Contact With Poison Hemlock

If you accidentally brush up against poison hemlock while you're hiking or hanging outside, you should be OK (remember: the whole rash thing is a myth). But if you accidentally eat it or it gets in your body, Dr. Shafer said you'll notice a few symptoms, including:

  • Feeling lightheaded
  • Sleepiness
  • Dilated pupils
  • Dizziness
  • Trembling

"People usually come in feeling unwell," Dr. Shafer said. Poison hemlock can cause muscle paralysis and death from respiratory failure, so this is not something you want to mess with.

If you're sharing a meal and people start to have symptoms of hemlock poisoning "everyone should go to the ER to get checked out," Dr. Shafer said. That homegrown "carrot" you ate could actually be poison hemlock, Dr. Shafer pointed out.

There's no direct antidote for hemlock poisoning, but Dr. Shafer said that people are "closely monitored" after being poisoned. "If they develop paralysis, they may need to be put on a ventilator for a few days," Dr. Shafer said.

How well someone recovers from hemlock poisoning depends on how healthy they were to begin with, Dr. Shafer said.

So, if you happen to see poison hemlock near you, it's really best to head the other way.

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