Isn’t the theory now that kids should be subjected to small amounts of nuts while they are young and thus build up a tolerance to nuts? Similar to the issues of parents who over clean the house or don’t immunize their children. Attempting to keep them safe and distant from anything that could harm them in the world actually leaves them defenseless when they actually go out into the world.
And don’t get me started on kids that grow up in gated communities and go to private schools . . . 
The truth seems to be they still really have no idea what causes allergies. In my wife’s case she developed the allergy later in life after her first pregnancy at the age of 28.
Before then she ate nuts and peanuts all the time. Loved peanut butter, Reeses, mixed nuts for snacks, etc. Then she had a few odd reactions out of the blue; watery eyes, itchy throat and sinuses, short of breath; figured out they were food related and went to be tested. Sure enough she had a severe allergy to nuts. Why now? They had no idea, she just did.
With cross-contamination always being an issue trying to find nut-allergy safe food can often be a challenge. Bakeries are pretty much off the list since every bakery in the world uses nuts somewhere and they make all the food in the same kitchen. No birthday cake unless you make your own. Chinese food is out since they use a lot of peanuts and peanut sauce in the kitchen. Starbucks uses hazelnut syrup and of course use the same blenders for all their frozen drinks so those are out. There was a pizza place we liked until they decided to add a hazelnut dessert pizza to their menu which pretty much contaminates the whole kitchen. The list goes on and on.
In general in order to have liability you need to be aware of the danger your actions are likely to cause. Since there is no way for you to know if someone has a peanut allergy then you have no liability unless you have been informed and bring it on the plane anyway.
The increase in peanut allergies was caused by a generation (or more) of hypervigilant parents who actively intervened to prevent their kids from having nuts - peanuts especially - when they were young, i.e. while their immune systems were learning tolerance.
Then, presumably, some years later, in some kids at least, an anaphylactic reaction was precipitated when Ashley/Adam tries their first peanut and jelly sandwich. As far as their (now mature) immune system was concerned, the peanut was foreign.
Clinically important peanut allergies are reduced by purposely exposing infants and little kids to peanuts when they are very young.
Is there anything to the thought that widespread smoke-free laws have increased the incidents of allergies. I’m not arguing against these laws at all, but it seems to me that if you are exposed to cigarette smoke from birth, even if your parents did not smoke, at every public place you go to then your immune system is getting practice at fighting off carcinogens.
I don’t think most carcinogens are “fought off” or otherwise neutralized by the immune system (we don’t make protective anti-asbestos antibodies, for instance, although there’s a link between asbestos exposure and development of autoimmune disease). The more exposure you get to carcinogens in general, the more likely they are to, um, cause carcinogenesis.
I’d expect the incidence of exacerbations of chronic respiratory disease (i.e. COPD and asthma (which may have an allergic component)) to have decreased thanks to anti-public smoking laws. And there’s some evidence to support that.
Omar’s story reminded me of the probably apocryphal story of a tiny village in England that finally got running water over a pump in the kitchen. One fellow figured the pipes would freeze so, wanting them accessible for replacement, mounted them on the outside of the walls. Sure enough, they froze and burst regularly.
From what I can tell as a father of a couple of boys who are 7 and 4, the kids with food issues typically don’t just have one- they have a whole raft of them at once.
I think there was maybe one kid in my grade level with a peanut allergy when I was a kid. Food allergies were rare enough that we pretty severely mocked a guy who claimed to have a lethal seafood allergy when we were in college; people just weren’t allergic to food, and in the really rare case that they were, they got hives or diarrhea or something unpleasant, but not life threatening. We just thought he was being overly dramatic. Which he probably was, considering his personality that was revealed over the next four years, but we had no concept of food allergies either- they seemed about as absurd as this same guy’s contention that he’d been hit in the chest by a basketball and his heart stopped. (or any of a half-dozen other melodramatic things that had supposedly happened to him)
A bit of clarification; my children have no food issues other than being irrationally fickle and picky from time to time.
They do however have classmates with food issues- and they seem to be an all-or-nothing kind of affair.
People are allergic to all kinds of things: could be groundnuts, could be strawberries, could be stray cat or dog hairs stuck to your coat. I stand by Omar Little’s and my advice that it is a fool’s errand to try to anticipate this, and there is no problem unless the airline explicitly prohibits bringing food on board, in which case they will say so.