The technical explanation involves the micellar surfactant structure, the close packing of particles and the effect these have on the film surface of the bubbles. But the basic conclusion is…
Oils depress foam
Oils also impact (usually reduce) viscosity
Some oil are worse than others because they impact the particle dynamics differently.
What can you do? Lots of things you can try but they may or may not work.
1. Use less EO.
2. Use a solubilizer like Polysorbate 20
3. Use different EOs
4. Don’t use EOs in your cleansing formulas
5. Adjust your surfactant levels (higher)
6. Reduce your salt levels (if you have any)
7. Use a thickener system that isn’t impacted by the micellar particle packing