One has to touch poison ivy (or something that has urishiol on it, like a pet, shoe, clothing, tool) to get poison ivy. If you know, for sure, you have not touched poison ivy, or touched something that touched poison ivy, you can know it's something else giving you a rash. I was shocked to find how many people are out there, investigating a mystery rash, usually from the same angle of "I know I didn't touch poison ivy but have the rash," yet there's very little info to help. Plants that definitely did not used to bother me before, propagated them many times, and definitely got sap on my skin, are now dangerous to me.
Nobody knows why sensitivity to previously harmless exposure to certain plants can suddenly result in dermatitis. Sensitivity to urishiol, and the plants below can be transient.
The details of the 2-year investigation might bore you, but in a nutshell, I'm suddenly susceptible to getting this rash from Aroids, heart-leaf Philodendron vines in particular. Test exposure confirms, that's (one of the plants) giving me a rash. A long lasting rash that's itchy enough to ruin sleep, scratch like a dog in public, be the foremost thought on your mind for about 8-10 days, and I don't know if some minor scarring is from too much scratching or would have happened anyway at what seemed to be the most exposed spots. Syngonium is another one. Rudimentary investigation leads to the word alkaloid. It's thought these plants have irritating alkaloids.
Interesting because Tradescantia zebrina and Callisia repens are also giving me a rash, and also contain alkaloids, though they are in the Commelina family. I'm suspicious of T. pallida also, but done experimenting. I've scratched enough.
Now also giving me a rash is anything with latex...
such as Ficus (fig, rubber tree)
Euphorbia (yard spurges and many potted succulents)
Plumeria (Frangipani, the Hawaiian lei flowers)
Ipomoea (morning glory, moonflower vine, sweet potato vine)
Sonchus (dandelion, sowthistle.)
What other plants contain latex sap?
Have you ever gotten a rash from a house plant? From gardening outside but you KNOW there's no poison ivy? Do you know anything (relative to contact dermatitis) about these alkaloids? Sources of more info? I don't understand much about the science, though I would read more info gladly.
I wanted to both raise awareness for those who would just prefer to avoid the sap of these plants instead of finding out if they can get a rash, and to help those investigating 'mystery poison ivy.' I would consider these plants at the top of a list to keep away from kids (plants to keep away from particular pets are well documented, and not an issue I have.) I'm also left with some questions, as asked here.
I'm not giving up any of these plants but definitely handling with caution when sap is exposed. By that I mean I intend to make sure I don't get any sap on my skin. I don't unknowingly trim or cut plants, so this shouldn't be too difficult, but might involve rubber gloves. As far as I can tell, once the sap dries, it's harmless. Once the site where a cut was made has healed over, it's harmless. Confirmation/disagreement? I'm leery about pulling off dead leaves, from T. zebrina in particular. They just don't want to let go. I know I'm compulsive about doing this, so if I end up scratching again and this was the only possible exposure, will report here. Going to try to train myself to cut them with a little scissors though. I have this stuff in many, many pots, as filler.
Couldn't find any reference to anyone getting dermatitis from casually touching the leaves of any 'house plants,' with the possible exception of some of the Ficus, F. benjamina in particular. No proof in the encountered anecdotes about 100% certainty the exposure was only casual. It seems a leaf could be bent enough to break open and expose sap, but 'fold' back to a normal looking position, making the rash seem to come from casual contact when there was sap involved, IDK. Am I willing to experiment - more? Nooooo way!
Edited to add: Also wanted to encourage anyone who gets a rash from a house plant to put that info in the plant database. Knowing beforehand can avoid a lot of misery.