M.linariifolia); however, other species may
qualify.^2
PHARMACOLOGY AND BIOLOGICAL
ACTIVITIES
Australian tea tree oil (M.alternifolia) exhi-
bits a broad spectrum ofin vitroantibacterial
activity that includes laboratory strains of oral
bacteria,^4 methicillin-resistant Staphylococ-
cus aureus,^5 Propionbacterium acnes,^6 and
Escherichia coli.^7 In vitroantifungal activity
from the oil is found against Malassezia
furfur,Candida albicans, and various other
species ofCandida.8–10Among eight compo-
nents of the essential oil, greatestin vitro
antibacterial (11 species) and antifungal
activities (C.albicans) were found from lin-
alool, followed by terpinen-4-ol,a-terpineol,
a-terpinene, and terpinolene.^7 (Linalool oc-
curs in only trace amounts in the oil.^2 ) The oil
has also shownin vitroactivity against herpes
simplex virus.^11
Essential oils from the leaves ofMelaleuca
(M.armillaris,M.ericifolia, andM.leucaden-
dron¼ M. cajuputi) have shownin vitro
antibacterial, antifungal (C. albicans), and
antiviral activities (HIV-1);in vitropotentia-
tion of catalase, superoxide dismutase, and
glutathione in erythrocytes; andin vitroinhi-
bition of lipid peroxidation.^12 BothM.alter-
nifolia leaf oil and terpinen-4-ol induced
differentiation of white blood cellsin vitroin
human myelocytic (HL-60) cells.^13
Contact hypersensitivity response and skin
swelling in mice were inhibited by topical
application of tea tree oil,a-terpineol, or
terpinen-4-ol; however, ultraviolet B- or irri-
tant-induced swelling was not suppressed.^14
Antitussive activity against capsaicin-
induced cough in guinea pigs was shown
from oral administration of tea tree oil and
from some of its main constituents (cineole,
terpinen-4-ol,a-pinene, andg-terpinene).^15
A clinical trial in 124 patients provided
evidence of the effectiveness of topical
M.alternifoliaoil in the treatment of moderate
(noninflamed) acne vulgaris. A 5% tea tree oil
in a water-based gel was less effective than
a 5% benzoyl peroxide in a water-based lotion
because of slower onset of action. However,
clinical assessment and self-reporting of side
effects indicated that the tea tree oil prepara-
tion was better tolerated by facial skin, pro-
ducing less skin scaling, dryness, pruritus, and
irritation than a benzoyl peroxide preparation
(TYLER1–3).^16 A study in 27 volunteers found
that topical application of tea tree oil inhibited
histamine-induced weal volume on the arm,
but not flare volume.^17 In placebo-controlled
clinical studies, symptomatic improvement
of tinea pedis was found from topical use of
a 10% tea tree oil cream;^18 reduced time
before re-epithelization was reported in pa-
tients using a 6% tea tree oil gel topically on
herpes labialis sores;^19 and reduced itchiness
and greasiness but not scaliness of dandruff
after using a 5% tea tree oil shampoo.^20TOXICOLOGYUse of tea tree oil for the topical treatment of
burn wounds is not recommended due to
in vitroinhibition of human epithelial cell
and fibroblast viability from 24 h exposure to
the oil.21,22Application of the pure oil to the
abraded skin of rabbits (Draize acute dermal
irritation test) resulted in increased skin irri-
tation, suggesting that the oil should not be
applied in cases of dermatitis.^23
There are a number of case reports of
contact dermatitis from topical use of tea tree
oil, including allergic contact dermatitis.23,24
No irritant effects were found in the skin
sensitization test in guinea pigs from tea tree
oil. No skin irritation was visible from topical
application of tea tree oil in a 30-day irritation
test in rabbits; no apparent signs of dermal
toxicity were found after 24 h exposure of
the normal skin to a high concentration of the
undiluted oil (2 g/kg). The healing of superfi-
cial dermal wounds in rabbits was neither
inhibited nor prolonged from topical applica-
tion of tea tree oil. Noin vitromutagenic
activity was produced by tea tree oil in the
Ames test.^23Cajeput oil 125