The chemical composition and biological activities of 19 essential oils and seven of their major components were tested against free and intracellular forms of
Leishmania chagasi
and
Trypanosoma cruzi
parasites as well as Vero and THP-1 mammalian cell lines. The essential oils were obtained from different species of
Lippia
, a widely distributed genus of Colombian plants. They were extracted by microwave radiation-assisted hydro-distillation and characterised by GC-FID and GC-MS. The major components were geranial, neral, limonene, nerol, carvacrol, p-cymene, γ-terpinene, carvone and thymol. The essential oil of
Lippia alba
exhibited the highest activity against
T. cruzi epimastigotes and intracellular amastigotes with an IC
50 of 5.5 μg/mL and 12.2 μg/mL, respectively. The essential oil of
Lippia origanoides
had an IC
50 of 4.4 μg/mL, in
L. chagasi promastigotes and exhibited no toxicity in mammalian cells. Thymol (IC
50 3.2 ± 0.4 μg/mL) and S-carvone (IC
50 6.1 ± 2.2 μg/mL), two of the major components of the active essential oils, were active on intracellular amastigotes of
T. cruzi infected Vero cells, with a selective index greater than 10. None of the essential oils or major components tested in this study was active on amastigotes of
L. chagasi infected THP-1 cells.