Regulation of Wheal and Flare by Tea Tree Oil: Complementary Human and Rodent Studies

Abstract

When applied 20 min after injection of histamine into human forearm skin, tea tree oil (TTO) reduces the developing cutaneous vascular response. In this study, the effect of TTO on inflammatory microvascular changes was dissected at the base of an experimental blister on rat skin. 1,8-Cineole, representing 2% of TTO, reduced vascular changes induced by sensory neuropeptides released when the distal portion of a cut sciatic nerve was electrically stimulated. The pre-terminal modulatory effect of 1,8-Cineole was confirmed in tests in sensory-denervated rats. Terpinen-4-ol (approximately 40% TTO) reduced substance P-induced microvascular changes and protein extravasation by a direct nitric oxide-mediated effect on the microvasculature, without sensory nerve involvement. alpha-Terpineol (3% of TTO) regulated both pre- and post-sensory nerve terminals. In human skin, terpinen-4-ol applied 10 min after histamine injection, but not alpha-terpineol or 1,8-cineole, regulated the developing wheal and flare suggesting that the histamine-induced responses in humans (at the dose used in this study, 50 microL of 330 microM histamine) are in large part determined by histamine directly affecting the vasculature via post-terminal-mediated events. The underlying strength of these studies is the use of a well-established rat physiologic model to differentiate the mechanism of regulation of microvascular changes by modulatory agents.

Treatment of acne with tea tree oil (melaleuca) products: A review of efficacy, tolerability and potential modes of action

“…In human studies, tea tree oil reduced experimentally induced skin reactions (nickel-or histamine-induced contact hypersensitivity) [50][51][52], which was suggested to be a result of decreases in vasodilation, microvascular blood flow and plasma extravasation [53]. Three non-acne clinical studies also report reduced inflammation following application of tea tree oil products for treating haemorrhoids [54], ocular demodecosis [55] and tinea [56].…”

Melaleuca alternifolia(Tea Tree) Oil: a Review of Antimicrobial and Other Medicinal Properties

“…Erythema and flare associated with nickel-induced contact hypersensitivity in humans are also reduced by neat TTO but not by a 5% TTO product, product base, or macadamia oil (119). Work has now shown that terpinen-4-ol, but not 1,8-cineole or ␣-terpineol, modulates the vasodilation and plasma extravasation associated with histamine-induced inflammation in humans (94).…”

Essential Oils and Antioxidants Derived From Citrus By-Products in Food Protection and Medicine: An Introduction and Review of Recent Literature

“…A study by Murakami et al (2000) identified citrus nobiletin as an effective, topicallyapplied inhibitor of skin inflammation, oxidative dermal stress response, and skin tumor promotion. A similar effect has been demonstrated using tea tree oil, which contains many of the same essential oils as those derived from citrus peel, in a parallel rodent-human study (Khalil et al, 2004). One explanation for the success shown by essential oils in skin treatment may be the extraordinary ability of these oils to penetrate the skin to the subsurface layers where active skin growth (and presumably inflammatory processes) occur.…”