From a book on advanced aromatherapy, I’ve learned that mixing essential oils into some commercial products can be unwise, depending on the ingredients in it. Because our skin has high permeability to EOs, mixing them with products having undesirable ingredients ( PEGs, for example) possibly could allow the unwanted ingredients to piggyback on the EOs and enter the skin.
I experienced this after adding lavender to a face cream I had used for years. After I added the EO, the cream stung when I applied it. I blamed it on the EO until I read about the permeability/piggyback issue. Lesson learned!