Magnesium ascorbyl phosphate (MAP) is a synthetic form of vitamin C that's used in many cosmetics and personal care products. It's a salt of ascorbic acid and magnesium, and it appears as a white or pale yellowish powder or granule. MAP is water-soluble and oil-loving, and it's considered the most stable form of vitamin C derivative. It's also non-irritating and antibacterial, making it suitable for sensitive skin.