During a medium depth peel, which skin layer is penetrated when the skin has frosted?

When a medium depth peel is performed and the skin develops a frosty appearance, it indicates that the peel has penetrated into the papillary dermis. The frosty appearance is a sign of coagulation of the proteins in the dermal layer, specifically within the upper portion of the dermis. A medium depth peel, typically using agents like trichloroacetic acid (TCA), is intended to reach this level of skin where more significant changes can occur compared to superficial peels.

The papillary dermis is the layer of skin just beneath the epidermis, containing connective tissue, blood vessels, and nerves that support the epidermis. By reaching this layer, the peel can effectively improve skin texture, tone, and address various skin conditions such as pigmentation issues and fine lines.

Reaching the epidermis alone would not produce the same level of change, while penetration into the reticular dermis or subcutaneous tissue is generally associated with deeper, more aggressive peels or surgical procedures, which go well beyond what is considered a medium depth peel.