Infrared spectroscopy for tracing of topically applied ointment vehicles and active substances on healthy skin.

Infrared spectroscopy was used to trace active substances and ointment vehicles applied on the skin. Vaseline and lanoline could be traced after 8 hrs but not olive oil. From the active substances, ethyl-4-amino-benzoate (5 per cent), clioquinol (5 per cent), parabenes (15 per cent), 5,7-dichlor-8-hydroxy-2-methyl-chinolin (5 per cent), balsam of Peru (25 per cent) and pyroleum pini (12 per cent) could be traced 1 hr after application but had disappeared after 8 hrs. Ethylenediamine (1 per cent), chlorcresol (1 per cent), pyroleum lithantracis (5 per cent), were not traceable after 1 hr, and curiously neither neomycine sulphate in spite of its high concentration (20 per cent). The reaction of the skin surface lipids, after application of different substances, was deduced from the spectra. Clioquinol and pyroleum lithantracis seem to give rise to hydrolysis of the triglycerides, the free fatty acids being clearly identifiable. It is felt that infrared spectroscopy can be used as an effective method to trace different substances such as potent allergens on healthy or diseased skin.