It is a recent trend in Korea that the uses of trichloroacetic acid(TCA) have been increased as the usual chemical peeling agent for treating abnormal pigmentation like solar lentigo, freckle, melasma, or actinic keratoses, rhytides, acne scar and other facial problems. We made an experiment to see how the different concentrations of TCA affect the guinea pig skin histologically.

The purpose of this study was to evaluate the histologic changes using various concentrations(35%, 50%, 90%) of TCA.

At first, 35%, 50% or 90% of TCA was applied to the each right ear of guinea pigs. After the application, we checked these specimens in intervals - one hour after (D_1hr), the following day(D₁), the third(D₃), fourth(D₄), fifth(D₅) day, one week(D_1wk), two weeks(D_2wks), six-teen weeks(D_16wks) later. The specimens were processed and stained with hematoxylin and eosin (H & E), Verhoeff elasic, and alcian blue stain.

1. In Do_1hr of 35% and 50% TCA treated groups, some keratinocytes with eosinophilic cytoplasm and pyknotic nuclei were scattered in the epidermis. The higher the concentration of TCA, the more evidence of homogenization of the epidermis. The homogenization of epidermis and dermis was most prominent in 90%.

2. In D₁ and D₃, necrosis of the epidermis was proportional to the concentrations of TCA. We could see infiltrates of inflammatory cells in the whole dermis-when 90% of TCA was tried.

3. Desquamation of the necrotic epidermis appeared in each group between 3 and 7 days after the treatment.

4. In groups treated with 50% and 90% TCA, reepithelialization arising from skin appendages was prominent.

5. Hyperplasia of epidermis appeared in every group between the second and sixteenth weeks but dermal hyperplasia was prominent only in the group of 90% TCA at sixteen weeks.

While thirty-five per cent TCA solution produced partial destruction of the epidermis, 50% and 90% of TCA destroyed the entire epidermis and upper dermis. Regeneration of epidermis from skin appendage is a signficant base of deep chemical peeling. Epidermal hyperplasia was found in 50% and 90% of TCA, but dermal hyperplasia was only found in 90% of TCA.