Allergy season
The period of elevated pollen concentrations in Croatia
The time of year when allergen pollen levels in the air are high enough to cause symptoms - in Croatia it runs from January to October in three main waves.
What it is
The allergy season is the time of year in which at least one allergen is flowering and releasing enough pollen into the air to cause symptoms in allergy sufferers. In Croatia the season runs from January (hazel, alder - the first heralds of spring) to October (ragweed, weed plants). Three main waves are tracked separately: early spring (trees), late spring and summer (grasses), and late summer and autumn (weeds).
How it is measured
The season of an individual allergen is determined by phenology - the biological cycle of the plant. Warmth speeds up flowering and cold delays it, but each species has its own window of a few weeks to a few months when it releases pollen. Climate change is shifting these windows: in Croatia the birch season has moved a few weeks earlier over the past 20 years, and the ragweed season has lengthened.
Sources and data
Season start dates by region have been tracked for years through Štampar's and local public health institute (ZJZ) measuring stations. The differences between regions are pronounced: olive in Dalmatia starts 6-8 weeks earlier than the tree season is even beginning for inland allergens, while ragweed in Slavonia has a markedly higher annual concentration than in Istria.
What you can do
Ways to reduce exposure during the season:
1. Follow the forecast - alergija.hr provides a daily forecast for 21 allergens across 6 regions.
2. Set up email alerts for your allergens with a threshold that matches your tolerance.
3. Prevention - an antihistamine 2 weeks before the expected start of your season reduces the intensity of symptoms.
4. Plan outdoor activities - on days at level 3 or higher, avoid being out in the early morning (the highest concentration in the air).
5. Shower and wash your hair when you come inside, to remove the grains that stick to your clothes and hair.
Context in Croatia
The three waves in Croatia:
• Early spring (January - April): hazel, alder, ash, willow, poplar, birch, oak. Birch is the most intense in late March and in April.
• Late spring and summer (May - July): grasses (Poaceae) are dominant. The peak is in May and June, lasting until the end of July. The longest continuous phase.
• Late summer and autumn (August - October): ragweed, mugwort, nettle, plantain. Ragweed is especially intense in continental Croatia (Slavonia, the Zagreb area).
Frequently asked questions
- Why has the allergy season lasted longer in the past few years?
- Climate change is lengthening the season in two ways: trees flower earlier because of milder winters, and weeds (especially ragweed) stay active longer into autumn because of a later first frost. In Croatia the overall allergy season has lengthened by about 3-4 weeks over the past 20 years, according to Štampar's pollen-monitoring data.
- I have symptoms all year round - isn't it just a seasonal problem?
- Seasonal pollen allergy is just one type. Year-round symptoms (perennial allergic rhinitis) usually mean an allergy to indoor allergens: dust mites, cat or dog dander, mould. The distinction matters because the treatment is not the same - talk to an allergist about testing if symptoms last more than 4 weeks outside your pollen season.
- How do I know when my specific season starts?
- On alergija.hr/kalendar there is a flowering calendar for 21 allergens, shown by month with intensity (weak, moderate, strong). In your profile you select your allergens, and the system sends you a notification 1-2 weeks before the estimated start of your season, based on historical data for your region.
- Is there a difference in the season between regions?
- Yes, a considerable one. Mediterranean Croatia (Dalmatia, Istria) has a longer tree season because warmer winters mean earlier flowering, and olive is a dominant allergen that does not grow in continental Croatia. Continental Croatia has a stronger ragweed season (Slavonia is the European epicentre of ragweed pollution). alergija.hr provides separate forecasts for 6 regions precisely because of these differences.
- When should I start medication before the season?
- Second-generation antihistamines (loratadine, cetirizine, desloratadine) are most effective if you start 1-2 weeks before the start of your season, not when symptoms appear. For severe allergy, talk to an allergist about nasal corticosteroids, which need 4-7 days of regular use to reach their full effect. Immunotherapy (SLIT/SCIT) is the long-term solution for severe cases and is started outside the season.