When a TCA peel results in a full frost, what layer of the skin has been reached?

When a TCA (trichloroacetic acid) peel results in a full frost, this indicates that the acid has penetrated through the epidermis and into the papillary dermis. The occurrence of full frost is a clinical sign that shows the effectiveness of the chemical peel and the depth of the peel's penetration.

In chemical peels, frost occurs as the TCA causes coagulation of the proteins in the skin, leading to a white appearance. This frosty appearance signifies that the peel has reached a sufficient depth to affect the papillary dermis, which is located just beneath the epidermis.

The epidermis is the outermost layer of skin, and if only this layer were affected, there would be no frost. The reticular dermis lies deeper than the papillary dermis, and while higher concentrations or prolonged contact with TCA can affect this deeper layer, full frost specifically indicates penetration to the papillary dermis. The subcutaneous layer, being even deeper, is not reached during standard TCA peels when frost occurs. Thus, the correct understanding is that full frost indicates involvement of the papillary dermis.