Some weeks ago, my elder grandson, age 4, had a reaction after eating a piece of cake in a restaurant - he developed a red face, severe headache and was violently sick. He was OK after a few hours, but the doctor recommended an allergy test - which he had last week. The test was pretty conclusive in showing that he has an allergy to tree nuts (Brazil, almond, cashew, etc.), but not peanuts, which are classed as a legume. So now we know.

A casual glance at Wikipedia tells me that tree nut allergy affects millions of people worldwide and is on the increase. What interests me is whether nut allergy - which can cause anaphylaxis and even death - is a comparatively modern phenomenon, whether it has always existed, or somewhere in between. If it has existed but is increasing, is this because of factors such as: growing use of chemicals in nut production; complex changes in diet, etc. Or has it always been around but unrecognised for what it is?

Anyone here got ideas as to origins? A Spanish friend of mine tells me that such nut allergies are "virtually unheard of in Spain" - but is her viewpoint skewed and, if not skewed, what's the world distribution of the allergy? And so on.