Giant hogweed is an herb that’s related to carrots, cilantro, and parsley. It grows naturally in the Caucasus Mountains, which stretch between the Black and Caspian Seas in Southwest Asia.

The plant was first introduced to the United States in 1917 for decorative planting. Its large size and delicate white flowers, which can sometimes be mistaken for Queen Anne’s lace, made it an attractive addition to gardens.

But the plant soon became an invasive and dangerous species because it’s harmful to humans and disturbs the natural habitat.

Giant hogweed sap can cause severe burns on human and animal skin. It grows very large and has the ability to spread quickly, allowing it to crowd out other plants that grow naturally.

Giant hogweed can be 15 to 20 feet tall when it’s fully grown. Thick stems, about 2 to 4 inches wide, support leaves that can reach 5 feet in width. Its clusters of small flowers can reach 2 1/2 feet in diameter and one bunch can produce thousands of seeds.

Currently, it’s been sighted in 16 U.S. states in the Northeast, along the Eastern seaboard, Midwest, the Pacific Northwest, and Alaska.

Giant hogweed isn’t dangerous as long as you don’t touch its sap. The sap inside the leaves and stalks is what causes burns. It has toxic chemicals called furanocoumarins.

When these come in contact with the skin, it causes a reaction called phytophotodermatitis. This reaction actually damages your DNA and changes the way your skin protects itself from ultraviolet (UV) light.

Phytophotodermatitis means your skin isn’t able to protect itself properly from the sun. If the skin gets exposed to sunlight, it causes a severe burn. This chemical reaction can happen as quickly as 15 minutes after getting the sap on your skin.

The longer sap is on your skin, the more sensitive skin can become to sunlight. Your skin may still be affected even months after exposure.

Redness and burn blisters can develop about 48 hours after exposed skin is in sunlight. The severity of the burn depends on how long you’re in the sun.

It can damage more than skin. If the sap gets in your eyes, giant hogweed can cause temporary or permanent blindness. Breathing in sap particles from the air can cause respiratory problems.

People often get sap on them when they don’t realize what the plant is. It can happen to a gardener chopping down weeds or kids playing in the woods — much like poison oak.

Most of the sap is located in the long hollow stem and the stalks that attach the leaves to the plant, so cutting this stem or tearing the leaves can release it. Sap is also found in the roots, seeds, and flowers.

Giant hogweed reaches 15 to 20 feet when it’s fully grown. Before that, the plant can get confused with plants that look similar, such as Queen Anne’s lace, because of its tiny white flowers that form in large clusters. But there are specific characteristics you can look for.

The easiest way to recognize giant hogweed is to look at the stem. It’ll have dark purple-red blotches and thin, white bristles. The green, jagged leaves can get as large as 5 feet wide. They may also have thin, white bristles.

If you get giant hogweed sap on your skin, wash the area with mild soap and cool water as soon as you can. Keep the skin covered when you’re outside to protect it from sunlight. The faster you’re able to wash off the sap, the less possible damage it can cause.

If a rash or blisters start to form, get medical attention. The treatment will depend on how severe the burn or reaction is. Skin irritation that’s caught early might be treated with a steroid cream and nonsteroidal anti-inflammatory drugs, such as ibuprofen, to relieve pain.

Severe burns could require surgery to graft new skin over the damaged skin.

In addition to having clothing over the blistered area when you’re outside, you’ll want to wrap it in gauze to prevent more sun exposure. Doctors may recommend you keep the area wrapped when you’re outside for several months, even after blisters are healed.

See a doctor right away if you get the sap in your eyes.

Giant hogweed is on the federal noxious weed list as Heracleum mantegazzianum. Because it’s considered an invasive plant, giant hogweed is banned from being planted and should be reported for removal if it’s spotted.

The plant usually grows in:

  • moist areas
  • woods
  • spaces with partial shade
  • areas along streams and rivers

Experts warn against removing the plant yourself. If you see giant hogweed, report it to the department of conservation in your state. There are different procedures in each state. For example, New York has a giant hogweed hotline you can call.

In general, you can find information on how to report the plant on each state’s department of conservation or environmental services website.

Giant hogweed is a dangerous and invasive plant. When the sap gets on your skin and the skin is exposed to sunlight, it can cause serious burns that require medical treatment, including surgery.

If you see the plant, don’t try to remove it yourself. Contact the department of conservation in your state.