What is the difference between hydration and moisture in skincare?

Hydration refers to the water content in skin cells — humectant ingredients like hyaluronic acid draw water into the skin to increase hydration. Moisture refers to the oil/lipid content of the skin's barrier — emollients and occlusives like squalane, shea butter, and petroleum jelly seal in water and prevent transepidermal water loss. Both are needed: hydrators attract water and moisturizers lock it in. Dehydrated skin lacks water; dry skin lacks oil.