Auckland Allergy & Eczema Clinic

Pollen Allergy and Cross-Reactions in New Zealand

Pollen Allergy and Cross-Reactions in New Zealand

By Vincent St Aubyn Crump

Seasonal Allergic rhino conjunctivitis (Hay fever) is one of the most common allergic conditions. It usually starts in early teens, and varies from trivial sneezing for a few weeks at the peak of the ryegrass pollen season, to severe debilitating rhino conjunctivitis, asthma and aggravation of facial eczema, lasting for up to 6 months in someone who is polysensitized to grass, weeds & tree pollens.

Perennial Ryegrass

Perennial Ryegrass

Perennial Ryegrass

In New Zealand the introduced plants are the most troublesome source of allergenic pollen. The plant causing the biggest problem here is the perennial ryegrass. It is the biggest pollen producer of all and the major cause of springtime hay fever. The majority of atopics are sensitive to it. The pollen, being small, will travel in the wind for many miles and the patient’s exposure is dictated by their proximity to grasslands and the prevailing wind. In New Zealand the pollen season varies, starting about one month earlier at the top of the North Island than the bottom of the south Island. In Auckland the main pollen season is between October and February, but because the seasons are so variable the pollen season is not well defined as in Europe and certain parts of the USA.

As general rule pollen concentrations are lower in coastal areas, but in New Zealand everywhere is surrounded by grazing lands and therefore experience high concentrations of grass pollen. Inland pastoral areas such as Hamilton and Palmerston North, for example, can have relatively severe seasons.


English Plantain (Plantago)

Flowering period: October to February

Plantains are extremely abundant weeds in New Zealand, growing in parks, lawns and roadside verges. Only small amounts of pollen are produced, but the pollen is very allergenic and plantain is a very common cause for hay fever in New Zealand.

English Plantain in flower

English Plantain in flower

Tree Pollen


Cupressus spp. are small to large evergreen trees commonly grown as shelter-belts on farms, or cultivated as ornamentals in gardens. One of the most cultivated species is C. macrocarpa.

Flowering Period: July to November

Allergens: These trees are big pollen producers, but probably not as clinically allergenic as the birch. My suspicion is that it is an underestimated cause for late winter — early spring rhinitis. More research is needed in this area.


Flowering period: July to October

Huge amount of pine pollen come from forestry plantations of pinus radiata. As with all pines, the pollen is not very allergenic, and only a very small proportion of patients with allergic rhinitis will be sensitized to it.

David Fountain, PhD, Director of Center for Plant Reproduction & Seed Technology at Massey University, has taken a particular interest in pine pollen largely because population surveys indicated "allergenic" people often cited pine as a problem. Pollen is produced in late winter in sufficient quantity to cover standing water with a yellow film and to be swept in clouds from trees. Lab experiments suggest that grass pollen probably cross-react with pine pollens. So it is theoretically possible that pine could cause some allergic problems in patients allergic to grass pollen.

It is my experience that very few patients react on skin prick testing (to any clinically significant level) to pine. Most of those who react to pine are strongly reactive to grass and will have a wheal size of less than 6mm to pine, supporting a botanical cross-reaction with grass. However, by virtue of the size, quantity and certain chemicals carried on the pine pollen surface, this pollen may cause some irritation in the nose if a large amount is inhaled. The reaction is more an irritant one as opposed to an allergic one.

Privets (Ligustrum)

Privets are hardy plants. This plant grows abundantly throughout New Zealand. It produces a highly scented flower, which is an irritant to most allergy sufferers, but is not a strong allergen. In doing skin prick tests in patients with allergic rhinitis it is very rare to get positive reactions to privet. Most people who think they are allergic to privet are actually allergic to ryegrass, which is not as visible as privet.


Flowering period: August to October

The silver birch (Betula pendula) was introduced from Europe and was therefore found in only a few areas. Because of its increasing popularity as a garden specimen and because it produces pollen abundantly, the birch is now the main tree pollen causing allergic symptoms in New Zealand. It is a very potent allergen.

The birch pollen is interesting because there is a very strong cross-reaction between birch pollen and several fruits (especially apples) and vegetables. This causes itching and swelling of the inside of the mouth, tongue & back of the throat when they eat fresh apples. These oral symptoms associated with birch pollen allergy is known as the Oral Allergy Syndrome.


Silver birch in flower

Silver birch in flower

Pollen Cross-reactions

In an allergic reaction antibodies are produced that are specific to each individual allergen. In other words the antibody should bind to only one type of antigen (allergen), like a tailor-made glove. Occasionally, gloves designed for one particular hand will fit another person’s hand that is of similar size and shape. Similarly, most grass pollens are of similar size & shape & will have areas that are almost identical. So antibodies produced against the ryegrass pollen will cross-react with timothy grass. Grass pollens are quite different from tree pollens; therefore there is not much cross-reaction between grass and tree pollens. Trees in the Birch family, Betulaceae (silver birch, alder & hazel) cross-react with each other, but very little with other trees & not with grasses. In New Zealand the silver birch is probably the commonest tree pollen causing ‘hay fever’.

Pollen Cross-reactions with Foods

There are also some fruit & vegetables that have similar & sometimes identical molecular appearance to pollens, and the antibodies produced against these pollens will cross-react with the fresh fruits & vegetables, mistaking them for pollens.

For the majority of hay fever sufferers, cross-reaction to foods is very mild and affect the mouth only, the so-called Oral Allergy Syndrome (OAS).

Oral Allergy Syndrome

Symptoms of OAS may include itching or swelling of the lips, tongue, throat, or roof of the mouth. Heating or digestion usually destroys the allergens causing these reactions. Therefore affected individuals can usually eat fruits or vegetables that have been cooked, baked, or canned.

OAS was first described in 1942 for apple & hazelnut, in patients allergic to birch pollen. Since then many other kinds of allergic reactions to various fruits and vegetables have been described in association with pollen allergy.

Allergy to fruits and vegetables occur most frequently in hay fever from birch allergy. In one study 35% of subjects with birch pollen allergy had positive skin prick tests to fresh fruits & vegetables. Another Scandinavian study, based on 2626 hay fever subjects, found 63% of birch allergic patients presented with allergy to 1 or more fruits or vegetables. Similar finding was reported in Austria, where more than 75% of birch allergic patients complained of allergic symptoms after eating apples.

These are some known cross-reactions, with the most commonly implicated fruits & vegetables listed first for each pollen:

pollen cross reactions.png

It is important to differentiate OAS from Food induced Anaphylaxis. IgE antibodies cause both reactions, but anaphylaxis is a much more severe food allergy. Anaphylaxis is usually a generalized reaction, which could include hives, breathing difficulty, swelling of the face and hands, wheezing or loss of consciousness. The foods commonly causing anaphylaxis include peanut & nuts, fish & shellfish, eggs and milk. However, some foods, particularly celery, seeds, or nuts, can cause either anaphylaxis or OAS.

Diagnosis of Oral Allergy Syndrome

The clinical history of oral symptoms occurring when a patient with hay fever eats fresh fruits or vegetables is almost certainly OAS. The diagnosis is confirmed with a skin prick test to all the local pollens & to the suspected (preferably) fresh fruits & vegetables, as the commercial extracts are very unreliable for fruits & vegetables. RAST can also be done.

Treatment of OAS

Antihistamines can reduce the symptoms to some extent.

There are recent reports of immunotherapy given for birch pollen, reducing the Symptoms OF OAS due to birch pollen.

Self help for Pollen Allergies

The height of the grass pollen (the main seasonal allergen) season in New Zealand occurs between October and Christmas and the major amount of pollen in the air occurs between 6.00am and noon. Although the pollen is known to be blown long distances on windy days, most pollen are deposited within a short distance of its source. The highest pollen counts occur on calm, hot, sunny days in late October, November and December. It is important to know that the tree pollen (like silver birch, wattle and oaks) allergy season starts in August and runs through October and weeds like plantain flower between October to February. In some individuals who are allergic to trees, grass and weed pollens their allergy season lasts from August through to March. The best treatment for allergy is avoidance

Avoidance of pollen is difficult but the following advice may help:

  • Make use of pollen counts. Pollen forecast is more helpful in pollen avoidance than retrospective counts (pollen counts related to the previous day).
  • Staying indoors until after midday (if possible) will reduce your exposure. Try to avoid going out on windy days.
  • Wear sunglasses to protect your eyes. The protective effect of the glasses can be improved by adding shields at the top bottom and sides of frames.
  • Do not mow the grass even when the grass is not in flower, and stay inside when it is being mown. If mowing is unavoidable wear a mask:
  • Cutting the lawn at frequent intervals will help it prevent from flowering, although grasses will adapt to regular mowing and may flower when very short. Make sure the edges of the lawn are trimmed, and the grasses are cut down in the weedy corners of the garden;
  • Keep windows closed both at home and particularly when in your car.
  • Ideally, a car with air conditioning will keep you cool and reduce the pollen load considerably.
  • If an air conditioned car is beyond your means, consider fitting a filter over the air intake, or install a car ionizer or air filter
  • Do not picnic in parks or in the country during the pollen season
  • Try to plan your holiday in New Zealand out of the pollen season or holiday at the seaside;
  • If you are sensitive to particular weeds or trees that are outside your bedroom window have them removed. Always have your allergies confirmed before, as many people wrongly blame privet for ryegrass pollen allergy
  • Shower (making sure you wash the pollen grains from your hair) when you arrive home and bathe your eyes frequently. Carry a supply of tissues.
  • Seek advice from your pharmacist and your family doctor about medications and treatments that will relieve your symptoms, remembering that most medications work best if taken before the symptoms get very bad.
  • For patients who still have severe symptoms despite taking all the simple precautions and medications there is the option of injection immunotherapy or desensitization.