Poison Ivy (Toxicodendron radicans) contains urushiol, an oily resin that causes an itchy, blistering rash upon contact.
Poison Sumac (Toxicodendron vernix) is another plant that produces urushiol, leading to severe skin irritation.
Stinging Nettle (Urtica dioica) has tiny hairs on its leaves and stems that inject formic acid and histamines into the skin.
Giant Hogweed (Heracleum mantegazzianum) produces a sap that contains furanocoumarins, which can cause severe skin irritation.
The Manchineel Tree produces a milky sap that is highly toxic. Contact with the sap can cause severe skin burns, painful blisters, and even blindness if it gets into the eyes.
Wild Parsnip (Pastinaca sativa) contains sap with chemicals that cause phytophotodermatitis. This reaction results in painful rashes and blisters when the sap is exposed to sunlight.
Wood Nettle (Laportea canadensis) has hairs on its leaves and stems that inject irritating chemicals into the skin.
Cow Parsnip (Heracleum maximum) produces sap containing furanocoumarins, which can cause skin irritation and blistering.
Poison Oak (Toxicodendron diversilobum) also contains urushiol, similar to poison ivy, and causes a painful rash
Gympie-Gympie (Dendrocnide moroides), also known as the “suicide plant,” has needle-like hairs that inject a potent neurotoxin.