Sweet chestnut (Castanea sativa) is a tree of warmer, hilly regions — it thrives in Istria, the Croatian highlands, on Medvednica, and elsewhere where soils are acidic and the climate mild. For allergy sufferers it is interesting primarily because it flowers late, when almost all other trees have long finished flowering, mixing its pollen with the beginning of grass season and thus extending spring-summer symptoms.

What plant are we talking about

Sweet chestnut belongs to the beech family (Fagaceae) — the same as oak and beech. This kinship is not just a botanical detail: it explains why sensitivity to chestnut often appears together with sensitivity to other members of the order Fagales.

It is important not to confuse it with horse chestnut (Aesculus hippocastanum), a tree of city tree-lined streets with white "candle" flowers — it is a completely different, unrelated plant and not significant for allergy sufferers.

Season

  • June and July, much later than birch, oak, and beech
  • peak usually mid-June, depending on elevation and year
  • late flowering means chestnut pollen overlaps with grass peak

How strong an allergen

Chestnut is classified as a weak to moderate allergen. Some pollen is carried by insects (the tree is known for chestnut honey), but a measurable amount is also released into the air, sufficient to cause symptoms in sensitive individuals — especially where stands are dense.

In measurements throughout Croatia concentrations are usually low, locally moderate in continental cities during peak flowering.

Symptoms

  • watery nasal discharge and nasal congestion
  • sneezing
  • itching and redness of the eyes
  • itching of the palate and throat
  • in sensitive individuals — worsening of asthma

Cross-reactivity

Due to belonging to the order Fagales, cross-sensitivity has been described with pollen from oak, beech, and birch. In practice this means that someone sensitive to spring trees may react to the later pollen of chestnut, and the symptom season imperceptibly extends into early summer.

Diagnosis

  • skin prick tests (prick) for chestnut as part of a tree allergen panel
  • specific IgE blood tests when skin tests are unreliable
  • symptom diary — symptoms persisting after birch and oak finish point to late allergens like chestnut

What helps

  • Second-generation antihistamines during the flowering period
  • Nasal corticosteroid spray for pronounced or long-lasting symptoms
  • Eye drops for allergic conjunctivitis
  • Ventilation at times of day with lower concentrations, avoid drying laundry outdoors

Note

This is not medical advice. If you suspect you have an allergy to sweet chestnut pollen or any other pollen, consult your family doctor or allergist. For symptoms extending from spring into summer, accurate diagnosis helps distinguish trees from grasses.