What indication shows that a chemical peel is penetrating too deeply?

Frosting, which appears as a yellowish-white coating on the skin during or after a chemical peel, is a significant indication that the peel has penetrated too deeply. This phenomenon occurs when the treatment damages the upper layers of the skin, causing protein coagulation. Frosting indicates that the peel has reached the deeper layers of the epidermis, which can lead to prolonged healing times and potential complications like scarring or hyperpigmentation.

The other indications, such as redness and swelling, can occur with many types of peels and are generally expected responses to chemical exfoliation; they do not necessarily indicate an excessive depth of penetration. Pigmentation changes may occur as a result of a peel, but they are not an immediate indicator of depth. Thus, frosting is the clearest sign of an overly deep chemical peel.