Japanese cedar trees (Cryptomeria japonica) are distributed widely across Japan, Taiwan and southern China and cultivated in Europe and North America as an ornamental tree. Cryptomeria pollen is a major allergen source associated with allergic rhinitis, asthma, atopic dermatitis and food-pollen allergy syndrome. Japanese cedar pollen shows high levels of cross-reactivity with other members of the Cupressaceae family including Japanese, Mediterranean and Arizona cypresses and mountain juniper. 

Worldwide distribution 

Cryptomeria japonica pollen is the most common allergen causing seasonal allergic rhinitis in Japan (2, 7). It can disperse >100km from its source, causing widespread pollinosis in major cities such as Tokyo and Osaka (3). There are regional differences in sensitization to Cryptomeria pollen across Japan, although these are relatively small compared to other tree pollens, due to the widespread distribution of cedar trees (7). In South Korea, Japanese cedar was the major outdoor allergen in spring only in Jeju district; this was attributed to localized cultivation of cedar trees (8, 9).

There appears to be a significant worldwide increase in the prevalence of cedar pollinosis (3, 10). In a 2008 national survey of Japanese otorhinolaryngologists, the prevalence of cedar pollinosis among their families was 26.5%; 10% higher than that recorded in a similar survey 10 years earlier (3).

Risk factors 

Co-morbid allergic rhinitis and a family history of cedar pollinosis increased the risk of both subjective and physician diagnosed Cryptomeria pollen allergy in Japanese patients (11). Repeated exposure to cedar pollen for over two seasons increased the risk of sensitization in Korean adults (12).

Pediatric issues 

IgE sensitization to Japanese cedar pollen is common in Japanese children at age 5 years and increases over time; this sensitization is clearly associated with allergic disease (10). In 2008, the prevalence of cedar pollinosis in Japan ranged from 1.1% in children aged 0-4 years to 31.4% in children aged 10-19 years (3). In another Japanese study, high levels of sensitization to the major Cryptomeria pollen allergen (Cry j 1) were found in 32.8% of children aged 5 years and 57.8% of children aged 9 years (10). A recent study of 258 pollen-allergic children aged 13 years found 95.7% were sensitized to Cry j 1 (13). Children sensitized to Cryptomeria showed clinical symptoms of wheeze, asthma, eczema and/ or rhinitis (10).

In a regional study of allergic Japanese children, cedar pollen-specific IgE was detected in approximately 60% of Grade 4 and 5 school children from inland sample areas, compared with 23% of children from a coastal sample area (3).

Worldwide distribution 

Cryptomeria japonica is a naturally growing endemic species in Japan and is widely used to create artificial forests (7). It is used in agroforestry for timber and fuel and cultivated as a boundary, shade, windbreak, or erosion control species and as an ornamental tree (6).

In Japan, pollen is often sampled using the gravimetric method via a Durham sampler, rather than the volumetric Burkard spore trap commonly used in Western countries (3).

Japanese cedar pollen is the most common cause of seasonal pollen allergy in Japan (1, 11). During the spring it contributes significantly to allergic rhinoconjunctivitis and sinusitis (2). Sensitization to cedar (defined as specific IgE levels of class 1 or above) was found in 78.8% of 382 young Japanese adults; the prevalence of cedar pollinosis was 41.2% based on self-reported symptoms and 22.2% based on physician diagnosis (11). Although cedar pollinosis peaks in patients aged 30–50 years, the age of onset is decreasing and it is now commonly diagnosed in children aged 5 years and over (3, 10).

Rhinitis and asthma symptoms can be exacerbated during Cryptomeria pollen season, even in patients who are not sensitized to this pollen. Both Cryptomeria pollen and its major allergen (Cry j 1) induced eosinophil adhesiveness, generated super-oxide anion free radicals (O₂^-) and released eosinophil-derived neurotoxin in non-sensitized healthy donors as well as in Cryptomeria-sensitized patients (14).

Asthma

Cryptomeria japonica pollen is a risk factor for bronchial asthma in Japanese adults (2). Seasonal increases in the level of pro-inflammatory eicosanoids in the bronchial mucosa of cedar-sensitized patients can reduce their pulmonary function, even when receiving maintenance treatment for asthma (15). Among 152 asthmatic and cedar-sensitized patients, asthma control worsened during the pollen season despite 84% of patients receiving concomitant treatment for rhinitis (16).

Atopic Dermatitis

Cryptomeria japonica pollen affects the severity of atopic dermatitis (2).

Other diseases

Of 76 Japanese patients with chronic obstructive pulmonary disease (COPD), 35.5% demonstrated specific IgE to Japanese cedar pollen (5).

Pollen from Cryptomeria japonica is an important factor in oral allergy syndrome (OAS) (2). Pollen food allergy syndrome (PFAS) refers to pollen-allergic patients who develop OAS on consuming fruits and vegetables. Age-independent studies suggest that 10-13% of Japanese patients with cedar pollinosis also have PFAS (13). Among 59 children aged 13 years with PFAS, the top causative foods were pineapple and kiwi, and 93.2% were sensitized to Cry j 1, the major pollen allergen of Japanese cedar (13).

Author: RubyDuke Communications

Reviewer: Dr. Christian  Fischer

Last reviewed:January 2022