What it is and where it grows
Alder is widespread in damp woodland, riverbanks and wetlands across the UK. A Latin name matters because “Alder” can describe a broad plant group or a particular species. The forecast row represents the configured CAMS variable for this group; its concentration is a model estimate, not a plant count.
For this pollen type, the configured UK seasonal window is January to March. That is a broad reference window, not a promise that every year begins and ends on the same day.
Who may react
Alder pollen can affect people with tree-pollen allergy, often before birch becomes the dominant spring tree pollen. A pollen forecast describes airborne concentration, not the chance that an individual will develop symptoms. Sensitivity varies, and symptoms can occur at concentrations that look low on a general scale.
If you have asthma or symptoms that are difficult to control, use the pollen exposure guide and follow advice from a healthcare professional.
How to reduce exposure
Check the type that you know affects you rather than relying on the overall “pollen” label. Wraparound sunglasses, changing clothes after time outdoors and drying laundry indoors are practical ways to reduce contact. The practical care guide explains these steps without promising that any one measure removes all exposure.
Across the UK
Latitude and local weather shift the timing. For this dataset, the numeric guide applies a 2-day delay per degree of latitude above the London reference, so northern locations generally reach the same seasonal stage later. Local planting and land use still matter more at street level than a national calendar can show.
On 2026-10-28, the London guide is the typical season ended about 30.1 weeks ago. Its calculated window is 1 Jan to 31 Mar.
Common misconceptions
- A zero forecast does not mean that every plant of this type is absent.
- A high daily peak does not by itself predict a person’s symptoms.
- National seasonal windows are not local start dates.
- Seeing this pollen in the data does not mean it is a significant allergen in the UK. This matters especially for olive and ragweed.