Some tree nuts contain different proteins to other nuts, so you could be allergic to walnuts but not cashew nuts. Careful allergy testing is needed to determine which nuts might be safe while others not. It might be safer for a person with a known allergy to one type of nut not to eat others
A few close shaves, Barry, usually when a product I'm used to and think I know the ingredients but one's been changed. Or if somebody uses Ground nut oil thinking it's safe.
I'm lucky though in that as soon as I bite into the food my tongue and mouth flare up as though I'm eating popping candy so I have an early warning.
We had a child who had a severe allergy to peanuts at one of the schools I worked in. He carried an epipen everywhere and we were taught how to use it. Anything remotely peanut related was banned and we were careful with nuts just in case although he didn't appear to be affected by them. Fortunately it was a village school and parents were usually happy to tow the line.
// One theory is that mothers in developed countries are now eating more nuts and peanuts when they are pregnant. This means their babies are primed for the allergy even before they are born.//