The oils in Rue (Ruta graveolens)contain a chemical called psoralens. When psoralens is exposed to Ultraviolet light (from the sun, sun-lamp, etc.) after it has been applied to skin, then the skin will blister or become brown or red as though it has been burned. The skin also becomes very sensitive. Some people will find the skin to become itchy.
This reaction is called phytophototoxicity. The reaction may not show up immediately but may pop up several days after the oils have been rubbed on the skin. So, if you develop strange markings on your skin and you've been working in the garden next to the Rue plant, you may have developed phytophototoxicity. Remember that the redness/blisters/etc. may not show up immediately. The pictures here were taken days after the reactions appeared. The pictured to the left, with blue markings, was taken after four days of having Rue leaves crushed and rubbed on the back of my hand (I was trying to determine what the reaction was from). Initially, NOTHING showed up. Two days later, the red mark appeared, much like a birthmark. On the third day, small blisters appeared.This next picture shows areas on my forearm ten days after having been exposed to Rue and not realizing what had happened. (This is what I saw first, causing me to do the 'experiment' with the crushed leaves in the first picture.). No blisters appeared on my arm but the marks were quite visible. No itching or pain accompanied the marks.
How to help with this reaction? I used an over-the-counter cortisone cream on both areas. On the spots with blisters, after the blisters popped, I applied Neosporin cream to help ward off infection. Sunscreen was applied after these creams.
Apparently, not much information is readily available with regards to this particular phytophotoxicity. Years ago, tanning solutions actually contained psoralens since it does make your skin sensitive to sun when it is exposed to ultraviolet rays. It was also used to treat psoriasis and vitiligo. Who knew?
It took almost two months for the discolouration to completely disappear from my forearm. I used an herbal skin lightening hand cream made by 'Kiss My Face' twice daily followed by sunscreen (the sunscreen was re-applied several times a day). The large blistered area from the top of my hand still is discoloured but this had been a large blister so it will probably take longer to heal.
So, keeping in mind that when handling Rue, particularly in the summer when the sun is high, be careful!
Note: Parsley and other members of the Apiaceae family also contain this naturally-occurring chemical. Whether or not the same reaction will occur is unknown to the editor.
