Which of the following examples of exfoliants would be considered physical?

Physical exfoliants work by physically removing dead skin cells from the surface of the skin through scrubbing or abrasive mechanisms. Microdermabrasion is a perfect example of this, as it involves the use of specialized equipment to spray fine crystals across the skin, gently buffing away the outer layer. This process helps to promote new cell turnover and can improve the appearance of the skin without the use of chemical agents.

On the other hand, lactic acid, salicylic acid, and glycolic acid are all chemical exfoliants. They work by dissolving the bonds that hold dead skin cells together or by increasing cell turnover rate through chemical reactions rather than through a physical scrubbing method. Each of these acids has different properties and benefits, but they do not fit the criteria for physical exfoliation. Thus, microdermabrasion stands out as the solely physical exfoliant among the given options.