My question is why are there only a few notorious allergic reactions but not a broad spread of people allergic to this or that?
We hear about nut allergies all the time. Touch a peanut and drop dead. Yet I have never heard of a broccoli allergy.
Why? What makes a peanut special versus (say) a carrot?
Broccoli hurts me to eat it. Happened suddenly after a procedure in hospital.
Couldn’t eat it anymore. I’ve tried small amounts a couple times. No go.
I can’t say it’s an allergic reaction. But it does cause GI issues. Mainly pain.
I think the answer is gonna be eosinophilic.
Peanut allergies appear to be primarily a reaction to certain proteins in peanuts, and the reaction becomes even more severe when the peanut is roasted.
Also, nuts, and peanuts, have a particularly high number of known food allergens.
Moderator Note
This is in FQ. Please hold off on personal experiences and guesses until the question has been addressed factually.
I don’t know the full answer, but I do know that foods that tend to cause allergies are also foods that have proteins that are not as easily broken down into simpler proteins that your body considers to be safe. This makes it easier for your immune system to identify those proteins, and therefore easier to mis-identify them as a threat.
As to why your immune system triggers on those proteins in the first place, that is beyond my knowledge.
Yet, a quick goggle search indicates they exist as do allergies to carrots. They’re just pretty rare. You as an individual can be allergic to damn near anything.
I think kenobi_65 pretty much nailed it. Randomly peanuts just have a greater than normal number of potential allergens including some that cannot be deactivated by heat. Why they have a greater number of potential allergens is a question best asked of a putative deity. Sometimes humans are just more commonly reactive to one thing than another.
Take urushiol. There is a wide variation in response. Some modest minority of people are highly resistant, but most people are mildly to severely allergic to the stuff. Which makes humans actually quite weird relative to the rest of the animal kingdom. Because the vast majority of birds and mammals are completely unbothered by it. Most browsers like deer and goats love poison oak - for them it is a tasty salad ingredient. So do birds. I always get a kick out of taking pictures of birds perched on it or even happily eating poison oak seeds. Urushiol does not seem to have been an evolutionary response to predators, but more likely developed as an antimicrobial defense. That humans, probably primates generally and, even more randomly guinea pigs, are allergic to it just seems to be down to the bad luck of the evolution dice roll. Some have hypothesized that it may be down to the fact that both primates and guinea pigs cannot natively synthesize vitamin C, but I believe that is unproven and contact dermatitis on the occasional dog isn’t explained by that. Might as well ask dogs why chocolate is potentially death or cats why onions are likewise. Some species are just randomly more sensitive to one environmental hazard than another.
Just because you’ve never heard of it doesn’t mean it doesn’t exist. My sister is allergic to all sorts of things - I bet you’ve never heard of an allergy to roach hair but she has it. The thing is, it’s a rare allergy and one you wouldn’t hear about if you didn’t have it or know someone who did. Mostly what you hear about is food allergies- and even then, mostly the ones that can be “hidden”. Fish and shellfish allergies are fairly common - but you don’t hear as much about them because there aren’t warnings about “may contain fish” or “processed in a facility that handles shellfish” because you don’t find fish or shellfish as an unexpected ingredient the way that deli meats might contain casein , a milk protein. There are people who have oral reactions to certain fresh fruits because those foods have similar proteins to pollens - for example, someone who is allergic to birch pollen may react when eating fresh carrots. And it’s mostly an issue with fresh, raw fruits and vegetables - cooking, freezing or canning breaks down the proteins so someone who never eats raw tomatos might not even know they would react to it.
This has a list of fruits/vegetables and the pollens they cross-react to.
Actually cockroach allergy not so rare, but dependent on exposure. Most common in poorer urban environments.
It is estimated that 30% to 40% of children with asthma are sensitized to cockroach in the inner city, with as many as 70% to 80% sensitized in some inner cities.41 In contrast, in one suburban population the sensitization rate was 21%.
As to the OP: yes a few foods dominate. In the US, just 9 foods (milk, egg, peanut, tree nuts, fish, shellfish, wheat, soy, and sesame) cause more than 90% of food allergies. And yes it’s the proteins.
Factors:
They don’t break down in digestion much. Tough nuts to crack so to speak.
Lots of the proteins in the foods and lots of targets fit to antibodies to latch onto.
How much of an irritant the protein is to the gut lining, which gets it into contact with the cells that effectively sound the alarm.
Timing and nature of exposure. Infants exposure to allergens through eczema (broken skin barrier) seem to very potent, and not only as eczema being a marker of allergy risk, as true cause agent. But early exposure through the gut can induce tolerance - hence dramatic recent reduction in peanut allergy after guidance to introduce peanut containing foods between six and twelve months.
Vegetables like broccoli lack most of those features so while they exist they are quite rare.
Funny, I was composing a post asking if it was simply proteins when you were writing this one. But part of my delay was reading that urushiol ( wiki from @Tamerlane) is an oil that reacts with the body’s proteins to form a new protein which causes the allergic response.
You’re explanation was really interesting – thanks!
There are a set of allergens known as the “Big 8” that are somewhat widespread. These are the alerghens that, if your food product contains it, you must give a warning on the label. There are laws in the US, Europe, Canada, Australia, New Zealand, and Japan that make you do this. (I don’t know about the rest of the world)
Some sources say that Sesame has been added, making it the Big Nine.
Curiously, seven of the Big Eight allergens have been shown to be de-activated by intense bombardment with deep ultraviolet light. Unfortunately, this doesn’t help if the product is opaque. No matter how bright your light is, it’s not going to penetrate fish, or peanuts.
The allergens, as noted, are proteins to which some people have a very bad reaction. Not everyone does. I don’t, as far as I know. In many cases, substitutes exist that can be substituted for the allergen-containing food.
The Big Eight are:
Dairy
Eggs
Fish
Shellfish (Crustacean)
Tree Nuts
Peanuts
Wheat
Soybeans
Remember that bad reactions to foods don’t have to be due to allergies.
Some foods cause problems due to food sensitivities or intolerance that don’t involve the immune system.
Broccoli for instance can (rarely) trigger a classic allergic/anaphylactic response, but also cause G.I. symptoms by a different pathway, i.e. salicylate sensitivity.
True story - I get migraines triggered by mussels. It took a few episodes to figure out that they were the common exposure. When my wife and I are out to eat, especially at a chef’s choice tasting menu experience, and we are asked if there are any food allergies, my wife is quite annoyed if I clarify not an allergy but can’t eat. “A normal person would call that an allergy …” 
Celiac too FWIW … not a gluten allergy. Favism …
It is largely just random, but primates and rodents are relatively closely related, so it’s not too surprising when we share some trait with them.
Theobromine is only about twice as dangerous to dogs as it is to humans. The differences are that, first, most dogs have much lower bodyweight than humans, and second, dogs will binge on much larger quantities of food than humans will.
I feel you. I have an intolerance to alcohol. I’m pretty sure that it’s not an allergy, since I think that ethanol is too simple a molecule to actually be an allergen. It’s probably an enzyme deficiency. But most people would just say that I’m “allergic to alcohol”.
Yeah, one of my sisters-in-law is Chinese and has the same enzyme deficiency (it is very common in East Asian populations). She has referred to it casually as an allergy though she is well aware it is not. She drinks a very small amount of sweet plum wine (gackk!) after meals sometimes, but does have to be careful about how much she imbibes or she will get an alcohol flush reaction.
Under EU law, there is a numbered list of 14 allergens that must be declared if present in food offered for sale. One of them is lupin, which I am not familiar with as a food, only as a flower.
From List of 14 Allergens | Food Safety Authority of Ireland
1. Cereals containing gluten, namely: wheat (such as spelt and khorasan wheat), rye, barley, oats or their hybridised strains, and products thereof, except:
(a) wheat based glucose syrups including dextrose
(b) wheat based maltodextrins
(c) glucose syrups based on barley
(d) cereals used for making alcoholic distillates including ethyl alcohol of agricultural origin
Crustaceans and products thereof
Eggs and products thereof
Fish and products thereof, except:
(a) fish gelatine used as carrier for vitamin or carotenoid preparations
(b) fish gelatine or Isinglass used as fining agent in beer and wine
Peanuts and products thereof
Soybeans and products thereof, except:
(a) fully refined soybean oil and fat
(b) natural mixed tocopherols (E306), natural D-alpha tocopherol, natural D-alpha tocopherol acetate, and natural D-alpha tocopherol succinate from soybean sources
(c) vegetable oils derived phytosterols and phytosterol esters from soybean sources
(d) plant stanol ester produced from vegetable oil sterols from soybean sources
7. Milk and products thereof (including lactose), except:
(a) whey used for making alcoholic distillates including ethyl alcohol of agricultural origin
(b) lactitol
Nuts, namely: almonds (Amygdalus communis L.), hazelnuts (Corylus avellana), walnuts (Juglans regia), cashews (Anacardium occidentale), pecan nuts (Carya illinoinensis (Wangenh.) K. Koch), Brazil nuts (Bertholletia excelsa), pistachio nuts (Pistacia vera), macadamia or Queensland nuts (Macadamia ternifolia), and products thereof, except for nuts used for making alcoholic distillates including ethyl alcohol of agricultural origin
Celery and products thereof
Mustard and products thereof
Sesame seeds and products thereof
Sulphur dioxide and sulphites at concentrations of more than 10 mg/kg or 10 mg/litre in terms of the total SO2 which are to be calculated for products as proposed ready for consumption or as reconstituted according to the instructions of the manufacturers
Lupin and products thereof
Molluscs and products thereof
Same general critter - but this is the food crop version. The flowers always look roughly the same. So lupins are always pretty, but not always good to eat. While the seeds of that first pictured species are generally edible (at least if slightly processed), by contrast this one is somewhat toxic. Don’t mix them up !
I see you’ve never tried braised lupin in lupin sauce.
In the US, most oats are processed in equipment shared with wheat products, so they’re not considered gluten-free. But we can get oatmeal that is labeled gluten-free that’s processed on dedicated equipment.
I’ve never even heard of a celery allergy. Google says that it is indeed rarer in the US than in the UK and Ireland.
Haven’t heard of this one, either.
Yeah, I have a friend with a celery allergy. Initially, I scoffed. But it’s true, and difficult because so many cured meats and sauces contain celery juice or celery powder. Friend is of Northern European extraction and also has the birch allergy constellation.
