Reduction of nickel-induced contact hypersensitivity reactions by topical tea tree oil in humans.
OBJECTIVE
Whilst the anti-microbial properties of tea tree oil (TTO) are established, the anti-inflammatory effects of TTO in human skin remain largely anecdotal and require evaluation. This study examined the effect of topically applied TTO on nickel-induced contact hypersensitivity reactions in human dorsal skin.


METHODS
TTO (100%), a 5% TTO lotion, a placebo lotion (no TTO), or 100% macadamia oil were applied at days 3 and 5 after nickel exposure.


METHODS
The flare area and erythema index were measured on days 3, 5 and 7. The regulatory effects of TTO were also investigated on the proliferative response to nickel or polyclonal mitogens by peripheral blood mononuclear cells from nickel-sensitive and control subjects.


RESULTS
TTO (100%) significantly reduced the flare area and erythema index when compared to the nickel-only sites. With respect to the erythema index, the anti-inflammatory effects were predominantly, but not exclusively, seen in a subgroup of nickel-sensitive subjects with a prolonged development phase of nickel-induced contact hypersensitivity response. The 5% TTO lotion, the placebo lotion and the 100% macadamia oil were all without significant effect. TTO significantly inhibited proliferation to nickel but not to non-specific polyclonal mitogens by peripheral blood mononuclear cells from nickel-sensitive subjects.


CONCLUSIONS
Topical application of 100% TTO may have therapeutic benefit in nickel-induced contact hypersensitivity in human skin. The mode of action of TTO requires further investigation, but may be an effect on the antigen presenting cells or the antigen presenting process in nickel-induced contact hypersensitivity, as well as vascular changes associated with this response.
Pearce
A L
AL
Department of Microbiology and Infectious Diseases, School of Medicine, Flinders University, Adelaide, Australia.
Finlay-Jones
J J
JJ
Hart
P H
PH
D000287:Administration, Topical; D000328:Adult; D049109:Cell Proliferation / Q000187:drug effects; D003877:Dermatitis, Contact / Q000188:drug therapy*; D005260:Female; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000166:cytology / Q000187:drug effects; D008297:Male; D008875:Middle Aged; D008934:Mitogens / Q000494:pharmacology; D009532:Nickel / Q000037:antagonists & inhibitors / Q000633:toxicity*; D008517:Phytotherapy; D020947:Tea Tree Oil / Q000008:administration & dosage* / Q000009:adverse effects / Q000494:pharmacology*
D008934:Mitogens; D020947:Tea Tree Oil; D009532:Nickel