A week after nightly creaming my face and arms with hydrocortisone I’m still itching. Each exposure makes the reaction worse next time. A few people, including our gardener, are lucky they don’t react to poison ivy, nor wildlife or pets protected by hair or feathers. Even after cautiously walking on a woodland path or weeding, the unwary can become victims simply by cuddling a canine companion who brushed against a vine.
Poison ivy is not strictly a poisonous plant although the allegation is rooted in the scientific literature as it belongs to the genus Toxicodendron, along with poison sumac and poison oak. The allergic irritant in its leaves, stem and root is urushiol, which presumably evolved to deter to grazing animals (and gardeners). I read that trace amounts exist in mango skins. Eek!
So potent is the oil that when microscopic droplets penetrate the skin, Langerhans cells recruit ‘armed’ T-lymphocytes to fight the invader. The process kills cells as collateral damage and causes blistering, swelling and a blazing red rash. As a slight consolation, my palms and soles never react because they have thicker layers of keratin.
Wakened at night by the urge to scratch, it’s hard to find a polite word for the irritant, but urushiol has a larger story. Once used in herbal remedies when plants were the basis of the pharmacopeia, it still finds a place in traditional Chinese medicine. Its anti-tumor properties encourage researchers to overcome insolubility in water to create a medication for testing in the body. I doubt they will find volunteers for a clinical trial !
Urushiol research is mostly based in Asia where it has long been used as a lacquer for furniture and other wood products. It is collected from lacquer trees, like tapping maple trees or rubber trees. The name of the tree in Japanese gave urushiol its name. Painted in thin layers, it oxidizes and polymerizes to a hard, stable coating.
If your arms become inflamed after resting on a table made in China, it wasn’t your mom’s scold that came back to haunt you from breaking domestic etiquette. The lacquer may not have cured completely.
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