Lighter, oil-based substances such as jojoba oil or squalene are classified as emollients. Emollients are typically unsaturated fatty acids that are prone to oxidizing. Oxidation is when components in the oil break down due to heat, light, and oxygen exposure, turning the product into a rancid, smelly, and unsightly mess (read: bacteria heaven). Therefore, they occasionally cause inflammation, clogged pores, and a spattering of acne. While they prevent some water loss, they are not the most effective moisturizers—something often masked by their ability to make skin feel smooth.