Poison Ivy

Poison Ivy is a common rash-inducing poisonous plant in the United States. These rash-inducing poisonous plants also include Poison Oak, Poison Sumac and Poison Hemlock. All of these plants produce an oily sap containing urushiol which causes an irritating allergic reaction and almost everyone is allergic to it. When the plant is touched or any object that has been in contact with the plant and contains the oils, you will get the itchy rash in that area. This rash is considered a type of allergic contact dermatitis. A small amount of only 50 ug of urushiol is enough to cause the allergic reaction and about 90% of the people that get in contact with it will develop the rash. (1) Figure 1 shows how these poisonous plants can be identified by their leaves. The leaf is the main way of identification, but all the plants are poisonous including the leaves, berries, stem and roots. (3)

Source and Appearance

Poison Ivy and other poisonous plants grows everywhere in the United States except for Alaska and Hawaii. People that perform activities like camping or hiking, gardening or landscaping, forest workers or house painting or roofing, are more prone to get in contact with Poison Ivy. As shown in Figure 1, Poison Ivy has three leaflets on each leaf that turn reddish during spring, green during summer and yellow, orange or red during fall. Poison Ivy grows as a shrub with white berries in western U.S. and as a hairy ropelike vine in eastern U.S. (1) In 2022 a study proposed the mechanism of action shown in Figure 2. Urushiol upregulates interleukin 33 which binds to receptors ST2 and Interleukin 1R mostly expressed in dorsal root ganglia. The binding of IL-33 to these receptors leads to an influx of Ca2+ creating the sensory response of itching. (4)

Mechanism of Action and Biotransformation

Florian Winau, an assistant professor from Harvard Medical School describes in 2016 the molecular pathway of Poison Ivy from the contact to the plant until development of the rash. When contact to the plant happened, urushiol gets in contact with Langerhans cells of the skin. These skin cells load urushiol into CD1a molecules which activate the immune system’s T cells. The T cells then produce interleukins 17 and 22 which are responsible for the inflammation and itching effect. (2)

Toxicokinetics and Target Organs

Absorption of Urushiol occurs through the skin after contact with the plant or by inhalation. When poisonous plants burn, release Urushiol in the air which may cause rash to your face and irritation on the nasal passages, mouth, throat and lungs. Longer exposure to the poisonous smoke can cause serious breathing problems. Allergic reaction occurs from 1 to 14 days after exposure but can be developed up to 21 days after exposure. When the rash starts the effects usually resolve within 2 weeks. (1)

Sign and Symptoms of Toxicity 

Signs and symptoms of Poison Ivy toxicity include itching rash, redness, swelling and blisters in the area of exposure which usually develops in stages from 1 to 14 days after exposure. (1) The following are the stages of Poison Ivy skin toxicity:

• Itching: After contact with the poisonous plant, intensive itching will start immediately, and the rash will eventually appear.
• Rash: From minutes to days after the exposure the rash will start to develop and for some people is an intense blistering rash.
• Fluid-filled blisters: Blistering can happen in the affected area at any point after exposure which will eventually break open and leaks fluid.
• Crusting and itching: With the time the break open blisters will crust over but the itching will still be present.

The rash can be on isolated spots only or covers a large area of the body. Rash can also develop in multiple areas of the body depending on how big the exposure to the plant was. Figure 3 shows examples of Poison Ivy rashes. (4) When exposure to poisonous smoke through inhalation, irritation of the nasal passages, mouth, throat and lungs can happen resulting in serious breathing problems. (1)

Carcinogenicity, Genetic Susceptibility or Heritable traits

There’s no evidence that Urushiol has the potential to be carcinogenic, genotoxic or teratogenic. Studies have found that Urushiol has the potential to be cytotoxic to cancerous cells and has suggested the use of it as a chemotherapy option for treating GI and colon cancer. (5) See the following article for more information about the use of Urushiol as a chemotherapy treatment for GI and colon cancer: Urushiol Induces Apoptosis via a p53-dependent Pathway in Human Gastric Cancer Cells – PMC (nih.gov)

Treatments and Biomarkers

There’s no diagnostic tests or biomarkers to identify a rash caused by Poison Ivy. Doctors usually look at the appearance of the rash and ask questions to the patient to identify a possible exposure to poisonous plants. To manage the exposure and get a fastest relief the following management steps are followed:

• Rinse your skin with soapy, lukewarm water to prevent the oil from spreading to other areas.
• Wash your clothes and everything that has been in contact with the Urushiol oil immediately to prevent further exposure to the oil.
• Avoid scratching as it may break your skin and cause an infection.
• If blisters are developed do not touch them, peel them off or remove the overlaying skin.
• Prevent infection by keeping the area clean and dry, notify your doctor if any signs of infection develop.

The Poison Ivy rashes are treated with anti-itch creams like calamine and hydrocortisone. When blisters start draining, astringent topicals with aluminum acetate can be used. Antihistamines like Benadryl can also be used to relief the allergic reaction effects. If irritation to the eyes, mucous membranes, mouth, nose or genitals occur, a steroid like prednisone can be prescribed. Antibiotics can be used if an infection occurs in the affected area. Applying cool compress to the affected area and lukewarm baths with colloidal oatmeal also helps to relief the itch.  (1) The following video by mayo clinic shows how to prevent and treat Poison Ivy rash.

Historical or Unique Exposure

Exposure to Poison Ivy and many other poisonous plants occurs all the time in the United States. From my personal experience, my father-in-law got in contact with one of these poisonous plants last summer when mowing the backyard. After a couple days, he developed a severe rash and nose, eyes and throat irritation needing to visit the emergency room. A couple weeks ago my niece also got poisoned by Poison Ivy by playing in her backyard developing the rash and blisters that get infected after a few days. These exposures from my family members shows that toxic exposure to any poisonous plant containing Urushiol can happen to anyone, anytime, and anywhere even in your own yard.

References

1. Cleveland Clinic. (2023, May). Poison Ivy, Poison Oak and Poison Sumac. Retrieved from Cleveland Clinic: https://my.clevelandclinic.org/health/diseases/10655-poison-plants-poison-ivy–poison-oak–poison-sumac
2. Powell, A. (2016, September). Harvard-led research team first to track molecular path of poison ivy. Retrieved from The Harvard Gazette: https://news.harvard.edu/gazette/story/2016/09/from-leaf-to-itch/#:~:text=When%20urushiol%20comes%20into%20contact,which%20cause%20inflammation%20and%20itchiness.
3. Labib, A., & Yosipovitch, G. (2022). Itchy Toxicodendron plant dermatitis. Allergies, 2 (1), pages 16-22; https://doi.org/10.3390/allergies2010002
4. Bennette, B. L., & Islas, T. (2021, June). Toxicodendron Dermatitis: Are you up to date? Retrieved from Wilderness Medicine Magazine (WMM): https://wms.org/magazine/magazine/1307/poison-ivy/default.aspx
5. Kim, S., Kim, D. H., Lee, S. H., Kim, M. J., Yoon, J. H., Chung, H. Y., Na, C. S., & Kim, N. D. (2013). Urushiol Induces Apoptosis via a p53-dependent Pathway in Human Gastric Cancer Cells. Journal of cancer prevention, 18(2), 169–176. https://doi.org/10.15430/jcp.2013.18.2.169
6. Mayo Clinic. (2018, June 19). Mayo Clinic Minute: How to treat poison ivy rash [Video]. YouTube. https://www.youtube.com/watch?v=G5mBkVdsoEE