692.1 - I think it would fit. The category says "excludes eczema of the external ear - 380.22", but I don't think they're saying dermatitis due to the toxic effect of an oil is the same as eczema, just because it happens to be on the ear. I think they're making a distinction between this, and eczema. I'd also assign an E-code, like E946.9, for example. If the note specifies it as an allegic reaction, though, you should probably go that route to find the diagnosis, which s in the 995.2X area.