| I never thought about it much but i used to have a similar reaction you did. I'm one of those in the "ignore it and it'll go away" camp which is why it never crossed my mind that something was amiss. First the background - about 15 years ago I was putting in a new garden wearing flip flops (sandals). I came in contact with poison ivy and had a lovely outbreak on the top of my right foot. Every year for the next 5 or 6 years, I'd break out in spring time in about the same spot on my foot. I assumed that I was coming in contact with poison ivy again as it was gardening time and I wasn't confident as to how to positively identify the plant (just the resulting rash). I've done a little research on the net and can find no information about recurring dermatitis. I haven't had the rash in the last 8 or 9 years and I have no idea why it went away. Just gone. Hmmm... I may have to do more research.
As far as I know, poison ivy does not naturally occur in Sweden but I'm not an expert. I did find an interesting reference to another plant that can cause skin reactions:
http://www.wnrmag.com/stories/2000/jun00/parsnip.htm
Just a bit of musings here... hope that your blisters stop their annual reappearance.
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