Aesthetic Dermatology MCQ - Trichloroacetic acid peel

A 45-year-old woman with actinic keratoses on the face seeks chemical peeling treatment. You decide to use a peel that acts by coagulating epidermal proteins, producing frosting proportional to depth of penetration. Which of the following peeling agents works primarily by caustic action?

A. Glycolic acid
B. Trichloroacetic acid (TCA)
C. Salicylic acid
D. Pyruvic acid
E. Azelaic acid

Correct Answer:
B. Trichloroacetic acid (TCA)

Explanation:
Peeling agents with caustic action work by causing coagulative necrosis of epidermal (and sometimes dermal) proteins. This leads to frosting, which indicates the depth of protein denaturation and correlates with the depth of the peel.

• Trichloroacetic acid (TCA) is the prototype caustic peel.

  • Concentrations <30% → superficial peel (epidermis)

  • 30–40% → medium-depth peel (up to papillary dermis)

  • 50% carries a risk of scarring and is generally avoided

Other options:

• A. Glycolic acid: Keratolytic (alpha-hydroxy acid) → breaks corneocyte cohesion, no protein coagulation.

• C. Salicylic acid: Metabolic action (sebostatic, comedolytic) rather than caustic.

• D. Pyruvic acid: Keratolytic, causes epidermolysis rather than coagulative necrosis.

• E. Azelaic acid: Primarily used topically for acne and pigmentation disorders; not a peeling agent with caustic action.

Key Point:
TCA is the classic caustic peeling agent, causing protein coagulation and frosting, making it effective for actinic keratoses, dyschromias, and superficial scars.