The effects of nine essential oils (ylang-wild, lavender, orange, ginger, chamomile, peppermint, sage, nutmeg, and eucalyptus), three known chemical penetration enhancers (tricaprylin, liquid paraffin, and mineral oil), and six plant oils (olive, sunflower, soybean, canola, corn, and grape-seed oil) on the skin permeation of p-aminobenzoic acid were studied using attenuated total reflection-Fourier transform infrared spectroscopy. We applied essential oil creams to the skin of volunteers and then used a high performance liquid chromatograph with a fluorometric detector to evaluate levels of p-aminobenzoic acid and its metabolites in urine that was not pretreated with solvents and directly injected into the liquid chromatograph. After 1–2 days of treatment with different formulations of essential oils, levels of p-aminobenzoic acid and its metabolites were higher in the urine of the participants treated with essential oils than in the urine of the untreated controls.
