Think of a facial essence as an illuminating moisturizer. Essences contain powerful humectants and emollients like hyaluronic acid and glycerin. As humectants, these ingredients act as magnets for water, drawing moisture into the skin and trapping it. But each humectant has its own unique benefits. Hyaluronic acid can carry 1,000 times its weight in water and bind water to skin cells; while glycerin molecules are smaller and can penetrate deep within the skin, carrying water into the inner layers of the dermis for deep hydration. As far as emollients, butters like shea and cocoa work to lock in hydration by preventing a natural function of the skin known as TEWL, or trans-epidermal water loss.