Pine trees (Pinus spp.) are distributed widely in the Northern hemisphere, both naturally and as part of commercial forestry. Although pine pollen was thought to have low allergenic potential, it is now an inhaled allergen of growing concern. Pine pollen causes allergic rhinitis, conjunctivitis and asthma in adults and children. Lung function deficits and reduced performance of the bronchial epithelial barrier are reported in clinical literature. There is a high level of cross-reactivity between Pinus species. Cross-reactivity to Cypress, Olive and Perennial Ryegrass allergens has been found in some studies. 

Worldwide distribution 

Pine pollen was long considered to be non-allergenic (8). However, sensitization to conifer tree pollen (Cupressaceae and Pinaceae) is thought to have increased dramatically in recent years; in a Spanish study of conifer pollen allergy, 11 of 499 allergic patients (2.2%) showed a positive skin prick test to Pinus pinea (9). Among 48 patients with suspected pollen allergy, 12% were sensitized to Pinus radiata; this may be primary sensitization to or allergic sensitization to other pines or cross-reactive species. (6).

Pediatric issues 

Aeroallergen sensitization to P. radiata was found in 7.5% of 371 skin-prick tests in pediatric patients studied over 5 years in Cova da Beira, Portugal (10).

The prevalence of ambient Pinus pollen on the day before and 3 days before assessment was associated with reduced lung function (when measured by forced expiratory volume in the first second [FEV1] and forced vital capacity [FVC]) in a cohort of 8-year-old Australian children (4).

Worldwide distribution 

The Scotch pine (P. sylvestris) is the most widely distributed conifer, used extensively in commercial forestry to produce softwood timber (6). The Monterey pine (P. radiata) originated in California and is classified as an invasive species, naturalizing in several countries including Australia, New Zealand, Argentina, Chile, Zimbabwe and South Africa (7). P. radiata is increasingly planted in the Mediterranean for rapid afforestation and as a timber source (6). The Black pine (P.nigra) has a wide but scattered distribution in mountainous areas across Europe and Asia (7).

Main

The main route of exposure is inhalation. The relatively large size of Pinus pollen may limit its exposure to the larger airways (trachea and bronchi); however, pollen grains can rupture into fragments small enough to penetrate the lower airways (4).

Pine pollen is sampled using a vacuum air sampler such as the Burkard spore trap (2) or a large flow pollen collector (1) and extracted using hydrofluoric acid (1) or ammonium bicarbonate (9).

Pine pollen is associated with allergic rhinitis, conjunctivitis and increasingly with asthma (9). It was previously considered of low allergological relevance (5) (6). Regional sensitization has been recorded in excess of 8%, so its clinical relevance is likely to be underestimated (6). Pine pollen is considered a plant allergen of emerging importance (9). Bacteria, endotoxins and molds found on Pinus pollen may contribute to respiratory symptoms in sensitized individuals (5).

Pinus pollen exposure is associated with decreased lung function test measurements (forced expiratory volume and forced vital capacity) (4). Components of P. sylvestris pollen reduce bronchial epithelial barrier functionality, via increased trans-epithelial electrical resistance and polarized release of inflammatory mediators by epithelial cells (11). 

Allergen immunotherapy

Due to the high number of allergic patients mono-sensitized to pine pollen, specific immunotherapy may be useful (8).

Avoidance

Avoidance may be impossible during the pollen season, due to the high prevalence of Pinus species throughout the Northern hemisphere and their global spread. Studies of pollen prevalence in Slovakia and South Korea found Pinus spp. to be the predominant tree pollen (2, 12).

Author: RubyDuke Communications

Reviewer: Dr. Christian  Fischer

Last reviewed:January 2022