Which of the following ingredients is commonly used in microdermabrasion?

Aluminum oxide crystals are commonly used in microdermabrasion because they are effective at exfoliating the skin. These tiny, sharp crystals create a mechanical action that helps to remove the outermost layers of dead skin cells, promoting skin renewal and improving its texture. The use of these crystals in microdermabrasion treatments allows for precise control over the level of exfoliation, making them ideal for various skin types and concerns.

Other ingredients listed, while beneficial in different skincare contexts, do not serve the same purpose in microdermabrasion. Glycerin is primarily a humectant that attracts moisture to the skin, Vitamin E is an antioxidant that helps protect and heal the skin, and citric acid is an exfoliating alpha-hydroxy acid that works through chemical exfoliation rather than mechanical. Thus, aluminum oxide crystals stand out as the go-to choice for the microdermabrasion process.