Category Archives: Allergy

Hay fever

=allergic rhinoconjunctivitis due to seasonal triggers, typically grass and/or tree pollen. First described by John Bostock in 1819! More likely if born in early months of year!

So itchy, swollen, watery eyes, runny and/or blocked nose, sneezing. Often itchy throat and ears too. Cobble stone appearance can be seen at the back of throat.

Not dangerous, but can seriously affect quality of life: poor sleep, poor concentration (exams usually at worst time of year), embarrassment about snot. One study showed children in England were less likely to get their predicted exam grades if they had hay fever, especially if prescribed sedating antihistamines.

Associated with other atopic conditions, such as food allergy and asthma. Under recognized as trigger for asthma exacerbations – pollen is too large to trigger the lower airways directly, rather pollen exposure in the upper airways trigger inflammation that travels down over a period of weeks to the lower airways. An exception is when pollen grains are fragmented, as seen in thunder storm asthma [Australia, Clin Exp Allergy. 2018;48:1421‐1428]

There are many different species of grass, but if allergic to one you tend to be allergic to all of them. Trees on the other hand vary, you tend to be allergic to specific groups of trees. In Europe the most important are birch (northern Europe) and olive (Southern Europe). Birch is related to alder, hazel, beech and oak.  Olive is related to ash.  Weeds belong to various unrelated families.

Hazel trees can start producing pollen in February, weeds can continue produce pollen through September! Moulds seem more associated with asthma than hay fever. Cypress blooms in winter! 

It’s not just pollen count – the amount of allergen carried by the pollen varies too. Correlate pretty closely but varies by time and place. Pollen potency varies (4-5 fold difference) geographically, especially grass. France has the highest yearly average grass pollen potency, 7-fold higher than Portugal. Olive pollen from two locations 400km apart varied 4-fold in their allergen potency – in Portugal there are times when pollen from Spain probably more of a problem for triggering hay fever than pollen from “local” trees! [Health Impacts of Airborne Allergen Information Network (HIALINE project)]


Watch the pollen count, and choose activities accordingly. Pollen levels fall in evening in countryside, but in cities not until 1am!

Closing windows, or at least not sitting near windows, washing hair, not drying clothes outside, pollen barrier balms.

Choose where you are going on holiday carefully!

Antihistamines – oral or nasal. Various, some people find one works better than another Sedating antihistamines eg Chlorphenamine should be avoided except at night. Nasal steroids useful if used correctly. Combination steroid/antihistamine available. Leukotriene receptor antagonist licensed for hay fever in children with asthma.

Short courses of oral steroids might be justified for special occasions.

Immunotherapy available – deaths reported in asthmatics with poor control.

Sublingual – age not important cf ability to hold in mouth for 2 minutes. Not approved by SMC in Scotland yet. Combined grass and house dust mite coming.

[Sian Ludman, St Mary’s]

For symptoms all year round (perennial), triggers such as house dust mite and pets are more likely.

Tree nut allergy

Group of nuts that includes hazelnut, almond, brazil nut, cashew, pecan, pistachio, walnut and macadamia. Definition of nut is actually a bit complicated, to do with whether the shell comes off spontaneously or not, but I stick to those defined by food labelling law.

Does not include peanut (a legume), coconut, pine nut, chestnut or tiger nut.

You can be allergic to just one, a couple or the whole lot. Risk of allergy to peanut is higher than if you weren’t allergic to anything.

Hazelnut and cashew allergies are common. Almond rare.

Hazelnut allergy goes along with fruit allergy and oral allergy syndrome.

Cashew allergy goes with pistachio allergy. Cashew allergy is particularly associated with anaphylaxis, even more so than peanut (but less common as allergy and allergen so less well known).

Pecan allergy goes with walnut allergy.

Hazelnut allergy

One of the tree nuts. One of the most common food allergens in the UK. Adults seem to get less severe reactions than children. Anaphylaxis rare compared with peanut and other tree nuts.

Hazel tree is related to birch, and indeed hazelnut allergy can be associated with tree pollen allergy (hay fever), as well as fruit allergies.

Cor a 1 is the least likely to cause systemic reactions, and then only with raw cf roast.  Cor a 8/9/14 associated with systemic, although 8 is LTP so may only be local (and likely fruit allergy too) – probably seen more often in Mediterranean populations. The others are storage proteins so more likely to cause severe reactions.

Cor a 9 and 14 seem most useful  – >1kU/l and/or >5 respectively give specificity of >90% and sensitivity of 83% in kids for “allergy with objective symptoms” viz more than just a tingle/itch. That translates to a negative predictive value of about 93% (PPV not given). [Dutch study, JACI 2013;132(2):393]

German study found  Cor a 14 had best AUC (0.89, cf 0.71 for whole hz).  Level of 0.35 gave 85% sensitivity with 81% specificity.  PPV doesn’t hit 90% until 47.8 though…

Bell pepper allergy

The names get confusing!

Bell peppers or sweet peppers (capsicum) come in red, yellow and green varieties.  The colour just tells you how ripe it is, they are the same thing! 

They are related to potato, tomato, aubergine, latex (the nightshade family).  You are not automatically allergic to all of these things, but you may have a higher risk if you are already allergic to one or more of them.

Chilli peppers are closely related to bell pepper.  There are lots of different ones, both red and green eg bird’s eye, Scotch bonnet, jalapeno, chipotle. 

Chilli powder, paprika, cayenne, pimento are all spices made from these plants, so if you are allergic to the vegetable there’s a good chance you will react to these spices too. These get used to make pepperoni, salami, chorizo sausage and others.

Black and white pepper are completely unrelated! You do not need to avoid these.

Cross contamination can be a big problem, since in restaurants, the same knife and chopping board will get used for chopping bell peppers and all other vegetables.  Chargrilled food is also a risk if cooked on the same surface as roast peppers! Ask restaurants to use separate knives, chopping boards, frying pan etc.

Ketchup, baked beans, BBQ sauce, crisp flavourings, stock cubes, soups are all potentially a problem, as are most ready meals, you will need to look closely at the ingredients label.

Paprika extract is used as red/orange colouring in lots of things.

You might need to avoid anything with unidentified ‘spices’ or ‘flavourings’ until you can get further details from the manufacturer.

You may not react if the amount of spice used is very low, but this is hard to predict and you may find that one time you don’t react but another time you do react to the very same thing. 

Abroad, food can be very different and you need to be much more careful.  In Serbia and Croatia, for instance, there is a traditional tomato sauce ajvar that often gets served on the side of meals, which is made with red peppers.

(With thanks to Julia Marriott)

Celery Spice Mugwort syndrome

An allergy syndrome, where there is cross reactivity between mugwort (a pretty nondescript weed, pollen can cause hay fever and trigger asthma) and a wide range of foods, including:

  • Fruit – esp apple, melon, peach, orange, watermelon
  • Tomato
  • Vegetables – esp  celery, carrot, green pepper, onion, parsnip
  • Spices – eg mustard, paprika, pepper, coriander, basil, dill, oregano, parsley, thyme, anise, caraway, fennel, tarragon
  • Chamomile
  • Sunflower seeds

You are not automatically allergic to everything, just be aware that you are at higher risk of being allergic to something else on the list if you are allergic to one or more things.

Mustard allergy

One of the 14 ingredients that must be highlighted on EU food labels.

Probably more common in France, not much data for UK but seems rare.

One of the spices that has cross reactivity with mugwort so look for other foods causing problems, as in celery spice mugwort syndrome.

Used in lots of different cuisines across the world eg black mustard seeds in curry, not just mustard as used on hot dogs and sandwiches. Also a key ingredient in:

  • mayonnaise (more usually the egg causes problems but could be either or both),
  • ready meals and other prepared foods,
  • Salad dressings,
  • Honey and mustard sauce eg for chicken, gammon,
  • Chutneys,
  • Pickles eg gherkins

Sometimes mustard leaf gets used as a vegetable!

Vaccine allergy

The most common adverse events of vaccines are fever, local pain or irritation, and local redness or swelling, which are not signs of allergy

With live vaccines, adverse effects can be delayed until 7 to 21 days after immunization; this includes vaccine-induced delayed-onset urticaria, which is commonly mistaken for allergy.

Assessment and allergy-focused clinical history

  • Testing appropriate for all, whether anaphylaxis, mild symptoms, unknown history or family history.
  • Gold standard is an oral challenge with a therapeutic dose of amoxicillin, 1hr observation, then 5 day course at home to ensure no delayed reaction.
  • Low risk individuals, where IgE mediated reaction unlikely, can go direct to challenge without testing.
  • Puncture and intradermal skin testing is recommended where reaction was within last 12 months, or there were respiratory symptoms. 
  • Skin testing using only penicilloyl-polylysine, with at least 5 mm of wheal and flare greater than wheal as the criteria for a positive test result, is now sufficient to rule out a high risk of having anaphylaxis during a confirmatory oral amoxicillin challenge

Egg is used in the manufacture of a number of vaccines. Whether this is clinically significant or not depends on the vaccine and the severity of the allergy:

  • MMR – only contraindication is anaphylaxis to MMR or other constituent of MMR vaccine
  • Influenza – (live nasal or inactivated injectable) patients with “severe anaphylaxis” (ie requiring intensive care) should be vaccinated in hospital.
  • Varicella, Rabies – no contraindication for egg allergy
  • Yellow fever – discuss with specialist if egg allergy

Gelatine (derived from pork or beef) can be a cause of allergic reactions esp MMR, Varicella, Japanese encephalitis. Allergy would usually be established from history of food reactions eg gummy/jelly sweets, marshmallows.

Latex – can be present in syringe or bung. See Latex allergy.

Despite these potential causes of allergy, immunisation can often be achieved through graded administration.

Fruit allergy

A range of possibilities!

  • Isolated type 1 allergy
  • Multiple type 1 fruit allergies – usually to similar fruit but also some common co-sensitivities eg banana and melon
  • Oral allergy syndrome – esp peach and related stoned fruit, cross reactivity with birch pollen (so hay fever), sometimes nuts too
  • Salicylate intolerance esp cherries, raw tomato, pineapple juice

Berry allergy

Some evidence of cross reactivity between raspberry and strawberry but there’s not much evidence to suggest cross reactivity with other berries.  There’s a theoretical link with blackberry, and other things in the same family (Rosaceae – massive group of fruit including apples, peach, pear, apricot, cherry).

Only one report of blueberry allergy ever!

Found one paper that said tree nuts, celery and parsley might also be related to berries, but again I think theoretical.