Patch testing to plants: sensitisation associated with exposure to plants, essential oils and botanicals in cosmetics

Contact allergy to plants, particularly Compositae, presents with dermatitis and is diagnosed with skin patch testing. Sesquiterpene lactone mix is a common screening allergen for plant allergy. The rate of plant allergen sensitisation in New Zealand, which is affected by local horticultural factors, has not previously been documented.

To investigate the rate of plant allergen sensitisation in New Zealand's regional population, characterise common allergens and reassess appropriate allergens for patch testing.

Retrospective analysis of patient demographics and patch-test results over an eight-year period (2012 to 2020) was performed at a tertiary patch-test clinic in Auckland, New Zealand.

820 patients completed patch testing. There was a 12.9% sensitivity rate (a positive reaction on patch testing) to at least one plant allergen and a 6.2% plant allergy rate (positive reaction of current relevance). The most frequent positive reactions were Myroxylon pereirae (n=38), colophonium (n=35) and sesquiterpene lactone mix (n=14). Of patients with a plant allergy (n=51), the allergy source was a botanical in a cosmetic product in 27 cases (52.9%), a plant in ten (19.6%) and an essential oil in two (3.9%).

Reactions to plant allergens were related to botanicals in cosmetics and creams, plants and essential oils. Rates of plant sensitisation in our cohort are comparable with international data.