Which ingredient is commonly included in moisturizing creams?

Glycerin is a highly effective humectant, which means it has the ability to attract and retain moisture in the skin. This property makes glycerin a staple ingredient in many moisturizing creams. When applied, glycerin draws water from the atmosphere and the deeper layers of the skin to the surface, helping to keep the skin hydrated and plump. By maintaining moisture levels, glycerin contributes to skin elasticity and overall skin health, making it an ideal choice for inclusion in products designed to provide hydration.

In contrast, salicylic acid is primarily used for its exfoliating properties and is beneficial in treating acne rather than providing moisture. Caffeine is often included in skincare for its antioxidant properties and may also aid in reducing puffiness, but it does not function as a moisturizer. Tea tree oil is known for its antimicrobial effects and is often used to treat acne or blemishes, not for moisturizing purposes. Therefore, glycerin stands out as the most appropriate ingredient for moisturizing creams.