Hi,
TCA cross treatment of deeper acne scars entails precise application of high concentration of Trichloro-Acetic acid (TCA) to the base of the scar. Frosting occurs when treated skin turns white due to irreversible damage done to the upper layers of the skin by the acidic solution. This frosting generally lasts 6-12 hours on the average.
Following the acute injury by the TCA cross, the skin initiates a healing process and the frosting fades. The frosting is first replaced by redness and swelling and later by scabbing over the following 5-8 days.
Hope this helps!