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The Cupressaceae family (16 genera and 140 species) is widely distributed throughout the world. The Cypresses are composed of 6 genera, and all are rather closely related: Cupressus (Cypresses), Juniperus (Junipers), Thuja (White cedars or Arborvitae), Libocedrus (Incense cedar), Chamaecyparis, and Callitris. They are distinguished by their small opposite or whorled leaves, which are usually scale-like, and their small pistillate cones with few scales. The pollen grains of this group are extremely uniform and spheroidal in form.

The Italian cypress tree (Cupressus sempervirens) is the most abundant plant in the Mediterranean area, followed by the Arizona cypress. The Juniperus genus is represented by Red cedar (J. virginiana), Mountain cedar (J. ashei), Prickly juniper (J. oxycedrus), and Juniper berry (J. communis).

There are approximately 60 species of Juniperus shrubs and small trees scattered throughout the Northern Hemisphere and the high mountains of the tropics. Red cedar (J. virginiana) is native to North America east of the Great Plains, from southeastern Canada to the Gulf of Mexico. Red cedar is a form of Cypress tree, not a true Cedar (genus Cedrus) but a variety of Juniper. Red cedar is the most abundant Juniper in all of the eastern United States and southeastern Ontario, appearing in fields and pastures and dry rocky places (1). 

In the USA, Mountain cedar (J. sabinoides) is a major cause of seasonal allergy in Texas and elsewhere in the Southwest. In Europe, this species is present only in the Balkan peninsula and the Crimean mountains (2,3).

Red cedar is a dense, evergreen, slow-growing tree that on poor soil may never become more than a bush. It grows about 5-20 m in height, with a trunk 30-100 cm in diameter. The bark is reddish-brown, thin, and fibrous, and peels off in narrow strips. The heartwood is bright purple-red to dull red; the sapwood is white. The sapwood develops a brownish tint in winter in the north and is sometimes used in windbreaks or screens.

The seed and pollen cones are found on separate trees (dioecious reproduction). The seed cones are 3-7 mm long and berry-like, with fleshy scales, and ripen into dark purple-blue with a white wax cover, giving an overall sky-blue colour (though the wax often rubs off). They contain 1 or 2 (rarely up to 4) seeds and are mature in 6-8 months from pollination. The fruit is ornamental when produced in quantity. Birds eating the fruit may “plant” it along farm fences and in abandoned fields.

The pollen cones are 2–3 mm long and 1.5 mm broad, shedding pollen in late winter or early spring. Pollination is entirely by wind. J. virginiana is a weak pollen producer compared with the notorious Mountain cedars (J. ashei and J. scopulorum), with their enormous pollen loads. However, it is still a significant cause of early spring hayfever, and occasionally asthma, in the southeastern states (1)

Red cedar wood is highly aromatic. It is used for pencils, posts, veneers, panelling, and clothes chests. Its oil may be used for the essence of soap and for use in microscopy. Red cedar and its oil were found to be effective for killing and repelling house dust-mites. (4) Juniper berries have a sweetish, resinous taste and are used for flavouring foods or gin.

IgE-mediated reactions

Although only sparse reports document sensitisation to Red cedar, anecdotal evidence suggests that asthma and hayfever are possible following exposure to pollen from this tree. Red cedar has been reported to be a significant cause of early spring hayfever, and occasionally asthma, in the southeastern states of the USA (1).

“Cedar” pollens may also be significant allergens in areas where they are prevalent but their effects have not been suspected. Red cedar and White cedar (Thuja occidentalis) are common plants in western New York State. In an examination of skin test results from 158 patients with asthma, rhinitis, or both, 102 had positive skin tests to at least 1 pollen. Among those, 52 patients (51%) had positive skin tests to at least 1 of the Cedar pollens. Patients sensitive on skin testing to Cedar pollen were very likely to be sensitive to deciduous tree, grass, or Ragweed pollen. The authors stated that sensitivity on skin testing to indigenous Cedar pollens was common in this region and therefore could be clinically significant (5)

Other reactions

uniper tar (cade oil) is distilled from the wood of the Prickly juniper tree (J. oxycedrus) and contains etheric oils, triterpene and phenols. It is used for many purposes in folk medicine. An individual who ingested a spoonful of homemade Juniper tar developed fever, severe hypotension, renal failure, hepatotoxicity, and severe cutaneous burns on the face. (6) Whether a similar result would occur from Red cedar is unknown.

The following allergens have been characterised:

• Jun v 1, a pectate lyase (7).
• Jun v 3, a thaumatin, a PR-5 protein (7).
• Jun v 4 (7).

Jun v 1 was shown to be highly homologous to the allergens of the Cedar pollens. Jun v 3 was also shown to be highly homologous to its counterpart in Mountain cedar (Jun a 3), but with some epitope differences. The findings of the study suggested that mutations in the genes or post-translational modifications may explain why Red cedar pollen is reported to be less allergenic than those of other members of the Cupressaceae and Taxodiaceae families (7).

Cross Reactivity

The group 1 allergens of other “Cedar” trees are reported to be a major cause of pollen hypersensitivity in several geographic areas, and allergens from several taxa have been shown to cross-react. Although cross-reactivity of Red cedar has not been elucidated, an inference of cross-reactivity with other pollens may be made from knowledge of its closely related genus member, Mountain cedar. For example, cross-reactivity has been reported between the group 1 allergen from Mountain cedar (Jun a 1) and Japanese cedar (Cry j 1) (8). High cross-reactivity (75-90% homology) has been reported between Cup a 1 (C. arizonica), Cha o 1 of Japanese cypress (Chamaecyparis obtuse) and Jun a 1, the major allergen of Mountain cedar; all have an active pectase lyase site (9). The authors concluded that the high degree of homology of Jun a 1 with Cha o 1 and Cry j 1 may explain the cross-reactivity of conifer pollens (10).

Similarly, Cup a 3 from C. arizonica, a thaumatin-like, pathogenesis-related protein (11), was shown to have a high homology with Jun a 3 from Mountain cedar (12).

Last reviewed: May 2022