Route Of Exposure

The species vary from 1 m shrubs to 20 m trees; some are deciduous, but the majority of species are evergreen. The plants can grow in soils that are very poor in nitrogen. Bayberry is a shrub or slender tree growing up to 12 m in height. The leaves are spirally arranged, simple, 2.5 to 12 cm long, lanceolate or wedge-shaped, shining or resinous, dotted on both sides, and with a crinkled or finely toothed margin. They have a fragrant odour when crushed.

The flowers are catkins, with male and female catkins borne on separate trees (dioecious reproduction), the male flowers in cylindrical yellow clusters and the female flowers in green, somewhat shorter clusters. The flowers appear in spring, generally before the leaves are fully expanded.

The fruit is a small drupe, which remains on the tree for several years and consists of clusters of round, 1-seeded, somewhat berrylike nuts covered with a greenish-white wax.

The wax coating on the fruit is indigestible to most birds, but a few species have adapted to be able to eat it. The seeds are then dispersed in the birds' droppings. The wax coating of several species of Myrica, including Myrica cerifera, is known as Bayberry wax, and was used in the past to make candles. The foliage of Myrica gale is a traditional insect repellent, used by campers to keep biting insects out of tents. Several species are also grown as ornamental plants in gardens. Myrica is used to spice beer and schnapps in Denmark.

Clinical Relevance

IgE-mediated reactions

Anecdotal evidence suggests that Bayberry may induce symptoms of hay fever in sensitised individuals; however, few studies have been reported to date; it is possible that the allergy occurs more frequently than has been reported, in particular as southern bayberry was reported to be the source of the fifth most common windborne tree pollen in Tampa, Florida, in the USA.

A 12-year-old girl reported severe symptoms when she contacted pollinating bayberry shrubs each spring; the shrubs had been planted as an ornamental hedge around her cottage. She reacted to bayberry (wax-myrtle) in skin tests, and inclusion of the allergen in her injection programme appeared helpful. Another patient, a 39-year-old forester with acute hay fever during spring with symptoms including sneezing, severe irritation of the eyes, profuse rhinorrhea and nasal occlusion, was evaluated. Skin tests by the pressure puncture technique revealed a three-plus reaction to bayberry pollen. Immunotherapy appeared helpful. The authors stated that they believed that bayberry (southern wax-myrtle) pollen was a significant inhalant allergen in the southern and south-eastern United States.

In a study of 400 consecutive subjects evaluated for allergic respiratory symptoms in this area, 15% had positive skin prick tests to bayberry pollen extract. When bayberry pollen extract was used to perform 25 nasal and 22 bronchial challenges on 45 of these subjects, 12 of 13 (92%) subjects with allergic rhinitis and positive bayberry-pollen skin-prick tests had positive nasal challenges. Four of 7 (57%) subjects with asthma and positive bayberry-pollen skin tests had positive bronchial challenges. Bayberry-specific IgE was present in the sera of 8 of 13 (62%) subjects with positive challenges, and absent in 15 of 18 (83%) subjects with negative challenges. Intradermal skin tests with bayberry pollen extract were more predictive of provocation challenge results than was plate radioimmunoassay.

Immunotherapy with bayberry extract has been reported to be of use.

Other reactions

The stem bark of a close family member, Myrica sapida, has been shown to possess not only bronchodilator activity but also to decrease bronchial hyper-responsiveness in animal models.