|In my late twenties I had the same reaction you described after eating cashews. Because Cashews, Mangoes and Pistachios are all from the Poison Ivy family I would say that you are having a skin allergy reaction to the oils in both the mangoes and cashews. You probably gave youself a double whammy by eating two from the same family. I would be careful of eating either of them in the future for it seems at least in my case to worsen with each outbreak.
I now avoid comming into contact with any of them. I must also be careful about comming in contact with people that are eating or handling them as well.