Oil
Essential oils are concentrated plant extracts, obtained through expression or steam distillation of flowers, bark, leaves, fruits and roots. Essential oils are highly concentrated and must be diluted with carrier oil before applying to the skin.

Silicone Oil
Silicone oils (polymerized siloxanes) are silicon analogues of carbon based organic compounds, and can form (relatively) long and complex molecules based on silicon rather than carbon. Chains are formed of alternating silicon-oxygen atoms (...Si-O-Si-O-Si...) or siloxane, rather than carbon atoms (...C-C-C-C...).