Some essential oils, such as Gaultheria procumbens, contain methyl salicylate, which is a cyclooxygenase inhibitor. As a result, some believe it may be of some use to treat tendinities (e.g., (1), although it is quite debated (2,3)).
The simplified mechanism is as follows (source: (4)):
Is there any way to improve the penetrability of oil used to treat a tendinitis (e.g., diluting the oil with some cream)?
I am mostly interested in the lateral epicondylitis of the humerus.
(1) Corrand, Laura. La place des huiles essentielles dans la prise en charge des douleurs articulaires et musculaires à l'officine. Diss. 2013.
(2) Matthews, P., et al. "Topical rubefacients for acute and chronic musculoskeletal pain in adults." (2011).