Why oil dissolves oil (and sunscreen)
The "like dissolves like" principle: oil-based cleansers emulsify oil-based residues — sebum, silicone-based SPF, makeup, and pollution-trapped lipids — without disrupting the aqueous barrier layer. Water-based cleansers cannot effectively penetrate oil-based residues regardless of surfactant concentration. The first cleanse with oil removes the fat-soluble load; the second water-based cleanse removes water-soluble residues and the emulsified oil cleanser itself.