July 04, 2025

Episode 31 - Son of a Birch! The Pollen Predicament

48 minutes

Show Notes

On this month's episode, Sue, John and Paul invite Darragh O'Hanlon (@thetopicalvet) onto the pod to discuss pollen allergies.

Chapter 1 – How Pollens Affect Animals

(02:32) John introduces the topic of pollen allergies and welcomes guest Darragh O’Hanlon.

Darragh shares how Sue’s lecture on otitis sparked his dermatology journey, and how John’s CPD also played a role.

(04:09) John asks how pollens cause allergic reactions in animals. Darragh explains that pollens are airborne reproductive grains from grasses, trees, and weeds, and describes their microscopic structure and typical transmission routes.

He shares the story of Mitzi the fox terrier, one of the first dogs documented with airborne pollen allergy.

(06:30) Sue asks whether pollens affect more than just the skin. Darragh explains that:

In dogs, pollens mostly trigger atopic dermatitis but can also affect eyes and ears.

Cats may show respiratory and skin symptoms, including asthma and eosinophilic conditions.

Horses show skin reactions like urticaria and, in some regions, respiratory issues like heaves.

(08:45) John asks why grass pollens are so problematic over say garden flowers.

Darragh notes a rising trend in grass pollen allergy and explains the volume and dispersal of wind-pollinated plants. Garden flowers are less allergenic due to heavier, insect-borne pollen; wind-pollinated plants like grasses and trees produce vast quantities of light airborne pollen. Sue discusses tree flowers and their pollen production.

(11:30) Sue asks which trees cause the worst reactions. Darragh highlights birch as a major allergen in Northern Europe. He explains its cross-reactivity with other tree pollens and regional variations such as cypress (Mediterranean) and cedar (Japan). Conifers and pines, though present in air samples, are less allergenic due to their size and resin content.

Chapter 2 – Seasons, Cross-Reactions, and Geography

(14:20) Sue asks about pollen season overlap and the role of allergy testing. Darragh agrees and describes how pollen calendars can predict seasonal challenges.

He outlines Ireland’s pollen calendar, from alder and hazel in winter through to weeds in autumn.

(16:20) John asks if pollens cross-react with each other or be linked to food sensitivities.

Darragh explains:

Cross-reactivity is common among grasses and within trees and weeds.

Birch is highly cross-reactive.

Some food cross-reactions exist in humans (e.g. Mugwort-Birch-Celery Syndrome), but evidence in dogs is limited.

(19:55) Sue mentions bee foraging and asks about using tape strips to detect pollens on animals. Darragh shares anecdotes and online interest in identifying pollens via tape stripping.

(21:36) Sue asks about ragweed in Ireland. Darragh says it’s rare locally but problematic in the US. He discusses its introduction to Europe and control measures.

(23:20) John asks how pet owners can reduce pollen exposure. Darragh shares advice:

Allergen avoidance is difficult; pollens travel long distances.

Regular washing, foot rinsing, and barrier-supporting shampoos help.

Avoid walking dogs on freshly cut grass or on high pollen days.

(26:10) John asks about environmental factors like altitude or proximity to the sea.

Darragh explains:

Pollen can travel thousands of kilometres.

Grass pollen is more localised than tree pollen.

Higher altitudes and coastal winds can reduce exposure.

(29:12) Sue mentions a 2023 study on reactions to grass sap, not just pollen.

Darragh reflects on cases that may fit contact dermatitis patterns seen with grass sap exposure.

Chapter 3 – Testing, Treatment & Takeaways

(31:14) Sue asks for practical advice on pollen avoidance and resources.

Darragh recommends:

Monitoring pollen forecasts (e.g. Met Office, Met Éireann).

Using allergy maps from dermatology providers.

Avoiding warm, dry, windy days; walking dogs after rain.

Understanding how weather affects pollen counts, including the impact of thunderstorms and urban pollution.

(35:15) John asks about immunotherapy and vaccine formulation.

Darragh explains:

Allergen-specific immunotherapy aims to desensitise.

Earlier intervention is better.

Cross-reactivity helps simplify formulations.

(38:36) Sue stresses that vaccine components must reflect relevant, local allergens.

Darragh notes the importance of seasonal coverage and discusses challenges with mixing mould and pollen extracts.

(41:05) Sue shares an anecdote about a mismatched allergy vaccine and wraps up with thanks to Darragh.

Useful Links:

Nextmune – Veterinary allergy diagnostics and immunotherapy.

https://nextmunelaboratories.co.uk/

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By elearningvet