What should be applied to a client's skin before a Jessner peel?

Before performing a Jessner peel, applying a prep solution to the client's skin is essential. A prep solution usually consists of a toner or other preparatory product that helps to cleanse and prepare the skin by removing impurities, oils, and any residual makeup. This step ensures that the skin surface is clean and ready for the chemical peel, allowing for better penetration of the Jessner solution and enhancing the overall effectiveness of the treatment. Proper preparation also helps to reduce the risk of irritation or adverse reactions during the peel process.

In the context of the other options, using a moisturizer might leave a barrier on the skin that could interfere with the peel's penetration. A cooling gel is typically applied after a treatment to soothe the skin rather than before, and an exfoliating scrub could compromise the skin's natural barrier and lead to potential sensitivities during the peel. Therefore, utilizing a prep solution is the most appropriate and beneficial step in preparing the skin for a Jessner peel.