Answer
Exposure to light, heat and air can promote oxidation. Oxidised components have greater potential to irritate or sensitise the skin.
Sources for this answer
- Care Tea Tree Oil 100% / Natures Aid Tea Tree Oil 100% — Current selected SmPCemc · Summary of Product Characteristics
- PubMedPubMed · Reputable Web
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.