For pollen allergy sufferers, the following three pollen types in Iceland are the main allergy triggers. All are fairly common:
- Birch (Betula spp.) – Betula pubescens, Betula nana
- Grass (Poaceae) – many species
- Docks and sorrels (Rumex) – Rumex acetosa, Rumex acetosella, and Rumex longifolius
Birch (Betula spp.)
Two species of genus Betula grow in Iceland. These are the downy birch (Betula pubescens) and the dwarf birch (Betula nana). Pollen counts do not distinguish between pollen of these species.
Like most trees, birches produce a large volume of tiny pollen grains, which are light and capable of travelling long distances when airborne in strong winds. Birch is one of the most potent allergens in the Nordic countries. In mainland Scandinavia, birch forests are common and birch trees begin to produce pollen already in April. It occasionally happens that a waft of birch pollen from abroad is detected in spore traps in Iceland before the Icelandic birch pollen season begins.
Spring weather, and temperature in particular, is a major factor in when the annual pollen season begins. In Iceland, birch can begin to bloom in the middle of May. Generally, pollen begins to be airborne in the later part of May. Pollen levels then peak either in late May or early June. Birch pollen is airborne for a period of 2–4 weeks, depending on the weather. Cold and wet weather can prolong the period during which birch pollen is airborne.
Birch allergy sufferers may also experience symptoms when alder blooms in March/April, since the major birch-pollen allergen is very similar to that of the alder.
Around fifty species of the grass family, Poaceae, grow wild or are cultivated in Iceland. Some are extremely common, others very rare. All produce pollen, which cannot be identified below the family level using an ordinary microscope.
Airborne pollen concentrations and the length of the grass pollen season depend largely on seasonal conditions. Grass pollen counts are usually low in June. Pollen levels peak in late July and early August in Iceland.
The first species to bloom in late May include meadow foxtail (Alopecurus pratensis). Grasses producing pollen in June include tufted hairgrass (Deschampsia cespitosa). Timothy-grass (Phleum pratense) blooms at the end of July. Bent (Agrostis spp.) often does not bloom until into August. Pollen from a shifting variety of grass species is thus airborne by the beginning of June and into September.
Docks and sorrels (Rumex)
Three species of genus Rumex grow in Iceland, in addition to several seldom-seen casuals (non-naturalised species). These species are: common sorrel (Rumex acetosa), red sorrel (Rumex acetosella), and northern dock (Rumex longifolius). These plants are in bloom for most of the summer, from June and into August, but pollen levels typically peak in the beginning of July. Rumex pollen is an allergy trigger, but it is not considered serious. People with grass allergies are also commonly allergic to dock and sorrel pollen.
Dock and sorrel pollen is airborne from early June and into August.
A number of other plant species grow in Iceland that are known allergy triggers. However, they are either so rare in nature or produce such little pollen that their effects are only felt in certain circumstances.