C. avellana (Hazel) pollen is capable of inducing allergic reactions at a concentration level of 20 to 30 grains per m3 per day (5). Several pollen species (birch, poplar, hazel, oak, and Artemisia) sensitive patients suffering from allergic rhinitis show symptoms such as congestion, runny nose, itching and sneezing (12). These chronic allergies cause physical weakness and reduce mental concentration. To overcome these issues, patients need to undertake several measures such as changing their lifestyle or occupation, following a specific diet, and avoiding allergens, continuing life-long symptomatic therapy, including immunotherapy (13).
Allergic rhinitis and Allergic Conjunctivitis
In a study conducted on 52 patients exhibiting allergic rhinitis (hay fever), 50% (26/52) were allergic to several tree pollens, like hazel, birch, oak, poplar, Artemisia (12).
A Central Europe based study was conducted on 625 atopic individuals suspected of allergy towards airborne pollen. The results reported 14.4% (90/625) of patients were sensitized to tree pollen allergen, and 11.36% (71/625) revealed positive SPT for Corylus sp. (hazel) pollen. Among these hazel sensitized patients, 53% (38/71) had a history of atopic dermatitis, 37% (26/71) with disseminated eczematous lesions, and 10% (7/71) had rhinitis and conjunctivitis (2).
Asthma
A study was conducted on 15-year records of allergenic pollens associated with 1311 allergic patients with asthma in Thessaloniki, Greece. An average yearly concentration of 3% was reported for Corylus spp. (hazel) pollen. 9.6% (126/1311) sensitive individuals exhibited positive skin sensitivity towards hazel pollen (7).
Atopic dermatitis
According to a study, 53% of patients exhibiting positive SPT towards hazel pollen allergens also demonstrated AD correlated symptoms (2).
A study was conducted between 2018-2019 in the Czech Republic on 81 patients (aged ≥ 14 years) with atopic dermatitis. Positive sensitization to hazel pollen allergen (rCor a 1.0101) was observed in 45.7% (37/81) of these patients (8).
Other topics
A 62-years-old Turkish female working on the farm was exposed to hazelnut leaves and complained about intermittent fever, respiratory distress, and cough for the last 20 years. Patterns of chronic exogenous allergic alveolitis with predominant CD8 cell was revealed through Broncho-alveolar lavage (BAL) testing. Serum analysis confirmed elevated titers of IgG antibodies against mold fungi derived from the culture of the hazel-nut husk (14).