Global Inhalant Allergen Reference

Birch

The most significant tree allergen across Northern and Central Europe and much of North America. Its major protein cross-reacts with apple, hazelnut, and stone fruits.

Where: Northern & Central Europe, Scandinavia, northern USA/Canada

Common reactions: Sneezing, itchy/watery eyes, and a runny nose; frequently triggers oral allergy syndrome — an itchy mouth or throat — after eating apples, hazelnuts, or stone fruits.

Oak

Extremely widespread across the Northern Hemisphere and a heavy pollen producer, though generally less potent per grain than birch or ragweed.

Where: Nearly all temperate Northern Hemisphere regions

Common reactions: Sneezing, nasal congestion, and itchy or watery eyes, generally milder per grain than birch or ragweed.

Japanese cedar (Sugi)

Japan's defining allergy — sugi (Japanese cedar) and hinoki (cypress) pollinosis affects an estimated 1 in 3 people in Japan each spring. Mediterranean cypress plays a similar role in southern Europe.

Where: Japan; Mediterranean Europe

Common reactions: Intense sneezing, nasal congestion, and eye irritation — regularly cited as one of the most severe pollen allergies worldwide.

Olive

Dominant allergen across the Mediterranean basin, where olive cultivation is dense — Spain, Italy, and Greece see especially severe seasonal rhinitis.

Where: Spain, Italy, Greece, wider Mediterranean; also California

Common reactions: Sneezing, conjunctivitis, and nasal congestion, often severe enough during peak season to disrupt sleep and daily activity.

Alder

One of the earliest pollens of the year, often overlapping with late winter — frequently the first allergy signal before birch season begins.

Where: Europe, northern North America

Common reactions: Sneezing and nasal symptoms much like birch's, and can trigger the same oral allergy syndrome with related tree fruits.

Plane tree (Sycamore)

Planted as an urban avenue and park tree across Europe because it tolerates pollution — which concentrates its pollen in dense city centers.

Where: Urban Southern & Western Europe

Common reactions: Nasal and eye irritation from its pollen, plus additional throat and skin irritation from the tree's fine seed-ball hairs.

Timothy grass

The reference species for grass-pollen testing and immunotherapy worldwide, thanks to its wide range across temperate climates.

Where: Temperate Northern Hemisphere

Common reactions: Sneezing, an itchy throat, and watery eyes — the classic hay-fever pattern, often worse on dry, windy days.

Rye grass

A dominant pasture and turf grass across Europe, Australia, and the Americas — a major contributor to spring/summer hay fever.

Where: Europe, Australia, temperate Americas

Common reactions: Sneezing, nasal congestion, and conjunctivitis, typically worsening right after mowing or during dry spells.

Bermuda grass

The dominant lawn and turf grass through hot, humid, and subtropical regions, where its long growing season means a correspondingly long allergy season.

Where: Southern USA, Australia, Mediterranean, subtropics

Common reactions: Sneezing and nasal or eye symptoms similar to other grasses, but over an unusually long season.

Ragweed

The most potent weed allergen known — a single plant can release roughly a billion grains in one season. Historically North American, now spreading through Central and Eastern Europe.

Where: North America (native); increasingly Hungary, France, Italy, the Balkans

Common reactions: Sneezing, nasal congestion, and itchy eyes; also linked to oral allergy syndrome with melon, banana, and zucchini.

Mugwort

The ragweed of the Old World — the dominant late-summer weed allergen across Europe and much of temperate Asia, including Korea and Japan.

Where: Europe, temperate Asia (Korea, Japan, northern China)

Common reactions: Sneezing, rhinitis, and conjunctivitis, with a well-documented oral allergy syndrome link to celery, carrot, and various spices.

Pellitory

A Mediterranean specialty with an unusually long season — in mild coastal climates it can release pollen for eight months or more of the year.

Where: Mediterranean coast, especially Italy and southern France

Common reactions: Persistent sneezing and nasal congestion, notable mainly for how much longer its season runs than other weed pollens.

Alternaria

Widely considered the single most clinically significant outdoor mold worldwide — strongly linked to severe asthma attacks when spore counts spike.

Where: Global; heaviest in agricultural regions, worst after summer storms

Common reactions: Rhinitis and conjunctivitis, but most notably a well-documented trigger of sudden, severe asthma attacks.

Cladosporium

The most abundant airborne mold spore on the planet by raw count, found on decaying plant matter nearly everywhere.

Where: Global, essentially everywhere with vegetation

Common reactions: Nasal congestion and eye irritation, and can worsen asthma, especially after storms stir spores into the air.

Aspergillus

Common both outdoors and in damp indoor spaces; of particular concern for people with asthma or compromised immune systems.

Where: Global, indoor and outdoor

Common reactions: Rhinitis and asthma symptoms; in people with weakened immune systems, can occasionally cause more serious lung infections.

Dust mite (D. pteronyssinus)

Thrives in humidity above roughly 50% — the reason dust mite allergy is markedly worse in coastal and tropical climates.

Where: Global, worst in humid/coastal/tropical climates

Common reactions: Year-round nasal congestion, sneezing, and itchy eyes; a major trigger for asthma flares and eczema.

Dust mite (D. farinae)

More tolerant of drier conditions than its European counterpart, making it the more common species across much of North America.

Where: North America especially; global

Common reactions: The same year-round rhinitis, asthma, and eczema pattern as its European counterpart.

Cat dander

One of the most potent indoor allergens known — so pervasive it's routinely detected in homes and offices with no cat ever present, carried in on clothing.

Where: Global, wherever cats are kept as pets

Common reactions: Sneezing, nasal congestion, itchy or watery eyes, and contact hives; a frequent trigger for asthma flares.

Dog dander

Levels vary significantly by breed, but no breed is truly hypoallergenic — all dogs produce some quantity of the allergenic protein.

Where: Global, wherever dogs are kept as pets

Common reactions: Sneezing, nasal congestion, and eye irritation, with contact hives and asthma flares possible in sensitized people.

Cockroach (Bla g 1/2)

Saliva, droppings, and shed body parts — not the insect itself — are the allergen source, and a major driver of childhood asthma in low-income urban housing.

Where: Global, worst in warm/humid urban environments

Common reactions: Nasal and eye symptoms, but most significant as a leading asthma trigger, especially in children.

Fine particulate matter (PM2.5)

Particles small enough to penetrate deep into the lungs; can also bind to pollen grains, making them more potent triggers.

Where: Global, worst in dense urban/industrial areas

Common reactions: Not an allergen itself, but irritates the airway and intensifies sneezing, coughing, and asthma symptoms from other allergens.

Ground-level ozone

Forms from sunlight reacting with other pollutants, so it peaks on hot, still, sunny days — often the same days pollen counts are highest.

Where: Global, worst on hot sunny days in urban areas

Common reactions: Coughing, throat irritation, and reduced lung function, commonly worsening asthma and existing pollen-allergy symptoms.