Botanicals in Dermatology: An Evidence-based Review

Juliane Reuter; Irmgard Merfort; Christoph M. Schempp


Am J Clin Dermatol. 2010;11(4):247-267. 

In This Article

8. Adverse Effects of Plant Extracts on the Skin

This section is not intended to address each commonly used botanical. It should rather stoke the awareness of clinicians for the eventuality of adverse effects and how they may present.

Virtually all herbal remedies may provoke allergic reactions, and several botanicals hold the risk of photosensitization. The prevalence of contact sensitization against some botanical compounds, such as oxidization products of monoterpenes, terpinene, balsam of Peru, and Compositae plants, is quite high in Europe.[146] Contact sensitization towards cosmetics containing plant extracts as a fragrance is increasingly reported. Such patients should avoid plant extracts in their personal care products.[147] Therefore, clinicians should not only be informed of the beneficial effects of botanicals for dermatologic disorders but also of specific adverse effects that might be caused by the use of herbal remedies.

Botanicals may cause phytodermatitis, which can be classified into non-immunologic, such as toxic or phototoxic dermatitis, and immunologic phytodermatitis, such as immediatetype hypersensitivity, allergic contact dermatitis, or photoallergic dermatitis.[20] An example of toxic phytodermatitis is the irritant phorbol dermatitis caused by the sun spurge (Euphorbia helioscopia).[148] Furocoumarins represent the principal agents responsible for phototoxic phytodermatitis. They comprise psoralens such as 5-methoxypsoralen (5-MOP, bergapten) and methoxsalen (xanthotoxin), which possess a distinct photosensitizing potential. Furocoumarins also occur in burning bush (Dictamnus albus) and garden rue (Ruta graveolens), which belong to the Rutaceae plant family.[149,150] Phototoxic skin reactions to psoralens include the Berlock dermatitis caused by 5-MOP, which is contained in cosmetically used Citrus bergamia (bergamot oil). Dermatitis bullosa pratensis is frequently caused by methoxsalen that mainly occurs in the Apiaceae family (Umbelliferae), which includes plants such as the giant hogweed (Heracleum mantegazzianum)[151] and various vegetables/herbs such as celery, parsnip, and parsley.[152]

Besides toxic and phototoxic phytodermatitis, some botanicals may cause allergic contact dermatitis sensitized to plants or plant products. The Asteraceae A. montana has been classified as a strong allergen according to sensitiziation studies with guinea pigs.[153] Its sesquiterpene lactones, especially those with an α-methylene-γ-lactone moiety, are the most important allergens responsible for inducing allergic contact dermatitis. In a recent clinical study, 443 patients were patch tested with Compositae mix, sesquiterpene lactone mix, arnica, marigold, and propolis. Other plant species from the Asteraceae family that also contain sesquiterpene lactones, such as tansy (Tanacetumvulgare), fever few (Tanacetum parthenium), yarrow (A. millefolium), or elecampane (Inula helenium), may also induce sensitization or elicitation of Compositae dermatitis. Chamomile (M. recutita) and marigold (C. officinalis) are different from the mentioned Asteraceae species.[154] As extracts of these plants are frequently used in occupational and cosmetic products, patch testing with additional plant extracts or adjustment of the commercial Compositae mix to regional conditions has been recommended.[155] However, the sensitizing potential of arnica may be overestimated. Recent studies have shown that arnica tinctures and sesquiterpene lactones are only weak contact sensitizers.[156,157] The potent anti-inflammatory effects of sesquiterpene lactones are dominant and fail to overcome immune regulation, which prevents contact hypersensitivity.[156] In essential oils such as peel oil from citrus fruits or tea tree oil from M. alternifolia, the allergens are oxidized degradation products of monoterpenes.[158,159] Tea tree oil has become one of the most common contact allergens. Moreover, tea tree oil and lavender oil have recently been reported to cause prepubertal gynecomastia.[160]

A recent review on the adverse effects of herbal drugs in dermatology summarizes the different sensitizing potential of herbal remedies, such as aloe vera, chamomile, or curcumin, and aromatherapy oils, such as lavender or tea tree oil.[161]


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