Focal, high-strength TCA has been used for ice pick scars for many years. We wanted to know whether the same idea works for boxcar and mixed (polymorphic) acne scars, which are wider and shallower and are usually treated with lasers.
What are boxcar scars?
Boxcar scars are round or oval depressions with sharp, well-defined edges. Unlike ice pick scars, the opening and the base are roughly the same width. Many patients have a mixture of boxcar, ice pick and rolling scars, which is why a single treatment rarely fixes everything.
What is TCA paint?
Trichloroacetic acid (TCA) is a chemical peeling agent. At high strength, applied only into a scar, it creates a controlled injury that stimulates new collagen from within the scar. In our technique, 90% TCA is painted into each scar with a fine cosmetic brush, so the surrounding normal skin is not treated.
How the study was done
Forty-one patients with boxcar and mixed acne scars were treated. Each had three sessions, spaced seven to nine weeks apart, and results were graded using the Jacob and colleagues scale.
The results
- All participants had good to excellent outcomes.
- Patients with skin types 3 to 6 had more excellent outcomes (59%) than those with skin types 1 to 2.
- Two participants (5%) had complications after the procedure.
- Five participants were taking isotretinoin at the same time, with no increase in healing time or complications.
Treating only the scar reduces downtime and cost, because the whole face does not need to be treated to improve a handful of scars.
Why it works well in darker skin
Full-face peels and aggressive lasers carry a higher risk of pigment problems in darker skin. Because TCA paint treats only the scar, far less skin is injured, which lowers that risk. In our study, darker skin types actually had more excellent results.
Can you have TCA paint while on isotretinoin?
Traditionally, patients were told to wait six to twelve months after isotretinoin before any scar procedure. In our study, patients on isotretinoin healed just as well. This means scar treatment can often begin earlier, which many patients value.
What to expect
- Treatment takes minutes; the scars frost white briefly.
- Small crusts form and fall off over five to seven days.
- Redness in treated scars fades over weeks.
- Three sessions are typical, spaced about two months apart.
Common questions
References
Sun C, Lim D. Trichloroacetic acid paint for boxcar and polymorphic acne scars. Dermatol Surg 2022;48(2):214–218.
Dr Davin Lim is a consultant dermatologist with a procedural practice in lasers, scar revision and pigmentation. This article is general information and not personal medical advice.
