severe egg allergy?

Allergies are a bit unpredictable at times. And allergy tests, though helpful, can also produce false positives sometimes. So, it is possible that your friend's son isn't really that allergic to eggs. However, it's also possible that he has a newly developed allergy to eggs. Sometimes it takes repeated exposures to a trigger in a sensitive person before allergy symptoms actually begin to occur. For example, as a child, I had 3 different cats. Then, as an adolescent, I developed a severe cat allergy that persists today, decades later.

The fact that your friend's son got egg on his skin without a reaction doesn't mean a whole lot, because food allergies are usually internal, rather than a contact (external) allergy. Although, this can also vary... I have a contact allergy to shellfish, but can eat it without any problems at all.

As far as nut allegies, it's true that people can have distinct reactions to different types of nuts. However, if your friend's child is allergic to peanuts, the allergist was probably trying to err on the side of caution by suggesting avoidance of all nuts.

With food allergies, one way to test actual sensitivity is by exposing the person to one possible allergen at a time, and then watching for allergy symptoms. This can be dangerous to do without medical supervision, however, as food allergies often trigger severe allergic shock known as anaphylaxis, which can be life-threatening if not treated immediately. So it would be wise for your friend to discuss the feasibility of doing such a thing with her child's doctor first.

I have the same with egg allergy. But sometimes it is the way things are prepared. I would not have a reaction if I broke an egg on me. But ingested I could go into shock and die. I can eat pancakes and no reaction but a hard boiled egg not. The doctor said it can be the way something is prepared or the concentration of the amount of egg in a product. Like I can eat mayo. So it is a weird thing but each person has to see what they can tolerated. My mom use to sneak (still does) into my food to prove I am not allergic and on the way to the hospital she will tell me "Oh there was cut up hard boiled egg in the food" It is real and it is bad, so just be understanding and helpful. Nothing worse than someone thinking you are faking when it can be life threating.