Hazel (Tree)
Description
Hazel trees (Corylus species) are deciduous shrubs or small trees belonging to the birch family (Betulaceae). They are recognized by their rounded, doubly-serrated leaves and production of edible hazelnuts enclosed in leafy husks. Hazels are commonly found in woodlands, hedgerows, and urban areas across Europe and parts of Asia. They produce distinctive yellow catkins in late winter that release abundant pollen before leaves emerge. Common species include common hazel (Corylus avellana) and Turkish hazel (Corylus colurna).
Allergy Symptoms
Hazel pollen commonly causes:
- Sneezing and runny or congested nose
- Itchy, watery, and red eyes
- Coughing and throat irritation
- Wheezing and exacerbation of asthma symptoms
Hazel pollen contains the allergen Cor a 1, which is closely related to Bet v 1 found in birch pollen. This means individuals allergic to birch often also react to hazel pollen. People with hazel allergies frequently experience Oral Allergy Syndrome (OAS), causing itching of the mouth and throat when consuming raw hazelnuts, apples, pears, cherries, peaches, and carrots. Cooking these foods typically reduces the allergic reaction.
Typical Pollination Period
Hazel trees are among the earliest pollinating trees, with timing varying by region:
- United Kingdom and Western Europe: Pollination can begin as early as January, peaking between February and March
- Central and Eastern Europe: Pollination typically occurs from February to April
- Other regions: Timing varies based on local climate but generally occurs in late winter to early spring
Geographic Distribution
Hazel trees are widely distributed across temperate regions:
- Europe: Common throughout, especially in woodlands, hedgerows, and as understory trees
- Asia: Found in Turkey, the Caucasus region, and extending into parts of China and Japan
- North America: Some species present, including American hazel (Corylus americana), though less prevalent than in Europe
Tips for Reducing Exposure and Managing Allergies
- Monitor local pollen forecasts and limit outdoor activities during high pollen days
- Keep windows closed and use air purifiers with HEPA filters indoors
- Shower and change clothes after spending time outdoors
- Use antihistamines or nasal corticosteroids as recommended by a healthcare professional
- Be aware of cross-reactivity with birch pollen and related foods if you have Oral Allergy Syndrome
- Consider allergy testing and immunotherapy for persistent or severe symptoms