TCA CROSS for acne scars how it rebuilds ice pick scars, and what recovery is really like

The basics

What is TCA CROSS?

TCA CROSS stands for chemical reconstruction of skin scars using trichloroacetic acid (TCA). Instead of peeling the whole face, a doctor uses a fine applicator to place a very small amount of high-strength acid into the floor of each narrow, depressed scar, pressing until the scar turns white, a change called frosting. Only the scar is treated; the skin around it is left alone.

The method was described by Lee and colleagues in Korea in 2002, in 65 patients with darker (Fitzpatrick IV to V) skin. The acid injures the lining of the scar in a controlled way. As it heals, new collagen is laid down inside the pit, and over several sessions the scar becomes shallower.

It is not the same as a TCA peel. A medium-depth peel spreads a lower strength, usually about 20% to 35%, across a whole area. TCA CROSS uses a much higher strength on pinpoint areas, which is why it should only be done by a doctor.

Which scars

Which acne scars TCA CROSS suits

TCA CROSS is designed for scars that are deep and narrow: ice pick scars, which look like large open pores, and narrow boxcar scars with steep walls. Most lasers do not reach the base of these scars, so building collagen from inside each pit makes sense. A 2026 review of 34 publications found it was used mainly for ice pick and boxcar acne scars, and also for chickenpox scars.

It is less suited to rolling scars, which are broad dips pulled down by bands under the skin. In a split-face trial of 20 Korean patients, a 1,550 nm fractional laser improved rolling scars more than TCA CROSS, while for ice pick scars the two did about equally well. TCA CROSS was less painful, but its downtime and redness lasted longer.

Raised scars (hypertrophic scars and keloids) and flat red or brown marks are not treated with TCA CROSS.

Strength

TCA CROSS concentrations doctors use

Published studies have used TCA at 50% to 100%, with 100% the most common. The original study used 65% in 33 patients and 100% in 32, and reported a good response in 82% and 94% respectively, with no significant complications. Since then, head-to-head studies have suggested that a higher strength does not always mean a better result.

In practice, the doctor chooses the strength and the amount of acid by scar depth, skin type and how your skin responded last time. More acid or a stronger solution is not automatically better; too much can widen a scar or leave a pale mark.

The procedure

How TCA CROSS is done, step by step

The steps below describe how TCA CROSS is generally done in studies and clinics. Your own doctor's instructions take priority.

• Assessment: the scars are examined under angled light and the narrow, deep ones are marked; rolling scars and flat marks are planned separately.
• Preparation: in several studies, skin was primed for two to four weeks with a lightening cream such as hydroquinone, a retinoid such as tretinoin, and daily sunscreen. At IN Eternity Clinic, exfoliating acids, scrubs and retinoids are usually stopped about a week before a 4D Scar Reconstruction session.
• On the day: the skin is cleansed and degreased, and a fine applicator carries a drop of acid into the base of each scar. A review found fine-gauge needles and fine brushes allow more precise placement than wooden toothpicks.
• Frosting: gentle pressure is held until the scar turns white. It stings or burns briefly; before a 4D Scar Reconstruction session at IN Eternity Clinic, numbing cream is applied for 45 to 60 minutes.
• Afterwards: the white frost fades to pink within hours, and small dark crusts form over the treated scars.
• Review: the next session is planned once the skin has healed and settled, usually several weeks later.

Downtime

Downtime and aftercare after TCA CROSS

TCA CROSS leaves a dotted pattern of small crusts rather than a raw face, so many people return to work within a few days if they do not mind visible dots. Crusts usually shed in about a week, and pinkness at each treated scar can last a few weeks. In the Korean split-face trial, downtime and redness lasted longer on the TCA CROSS side than on the laser side, and higher strengths tend to crust for longer.

Asian skin

PIH risk in Asian skin, and how it is kept down

Post-inflammatory hyperpigmentation (PIH), temporary darkening after skin injury, is the most common side effect of TCA CROSS. Across studies it was reported in roughly 7% to over 60% of patients and was described as transient, lasting weeks to months. Pale patches are less common, and a few reports describe scars that widened or deepened, mostly when a sharpened wooden applicator was used.

Much of the research was done in darker skin. In 30 patients with skin types IV and V, treated with 100% TCA after two weeks of priming, 73% had more than 70% improvement after four sessions; one had temporary lightening and two had temporary darkening. That is encouraging, but small studies cannot rule out problems in an individual.

• Do not have TCA CROSS while tanned or sunburnt; Singapore's UV is high all year.
• Follow the skin preparation your doctor prescribes.
• Expect a cautious strength at the first session; a 2026 review suggested gaps of six to nine weeks for strong solutions or darker skin.
• Use broad-spectrum sunscreen daily, and reapply outdoors, for the whole course.
• Let the crusts fall off on their own.
• Tell the doctor about any new darkening so the next session can be adjusted.

Sessions and results

How many TCA CROSS sessions, and what results to expect

Most studies used three to six sessions, four being the most common, with two to four weeks between them, although the 2026 review suggested four to six weeks to limit complications. In the original study, everyone in the 100% group who had five or six sessions had excellent results. In 53 patients treated with 70% TCA, 66% had good or excellent improvement (more than 50%) and 81% were satisfied; faces with mainly boxcar scars did better.

The 2026 review, covering 937 patients, reported improvement rates generally between 50% and 80%, with high satisfaction. Most studies were small and many had no comparison group, so the figures are encouraging rather than definitive. Scars become shallower and less obvious; they rarely disappear.

Collagen builds slowly, so improvement continues for weeks to months after each session. Compare photos taken in the same light and position, and judge the result a few months after the last session.

In Singapore

TCA CROSS in Singapore: part of 4D Scar Reconstruction

TCA CROSS is a medical procedure. In our network, Dr Sin Yong performs it at IN Eternity Clinic, 9 Scotts Road, #12-01 Pacific Plaza, beside Orchard MRT, as one of the four tools in his 4D Scar Reconstruction protocol: TCA CROSS for narrow, deep scars, subcision for tethered rolling scars, fractional CO2 laser for the surface and edges, and an injectable where volume has been lost. Not everyone needs all four, and the order is set at consultation. It is priced at consultation by the clinic; WhatsApp +65 8815 3008.

SkinRev Lab, at CityLink Mall #B1-28, linked underground to City Hall and Esplanade MRT, is a non-invasive centre. It does not perform TCA CROSS, prescribe medicines or give injections. It can help calm breakout-prone skin and refine the surface, and it passes scar enquiries to the clinic.

Safety

Who should wait, and why not to try it at home

High-strength TCA is sold online for home use, but placing it into scars is a medical procedure. Too much acid, or acid running onto normal skin, can cause burns, wider scars, infection and lasting pigment change, which are harder to treat than the original scars. See a doctor instead.

• Active acne in the area: control the breakouts first, or new scars keep forming.
• Infection, broken skin or a cold sore near the area.
• Recent isotretinoin: timing is discussed individually with your doctor.
• Pregnancy or breastfeeding: elective procedures and some preparation creams are usually postponed.
• A tendency to keloids or thick scars.
• A fresh tan or sunburn.

Sources

References & sources

1. Lee JB, Chung WG, Kwahck H, Lee KH. Focal treatment of acne scars with trichloroacetic acid: chemical reconstruction of skin scars method. Dermatol Surg. 2002;28(11):1017-1021.
2. Khunger N, Bhardwaj D, Khunger M. Evaluation of CROSS technique with 100% TCA in the management of ice pick acne scars in darker skin types. J Cosmet Dermatol. 2011;10(1):51-57.
3. Agarwal N, Gupta LK, Khare AK, Kuldeep CM, Mittal A. Therapeutic response of 70% trichloroacetic acid CROSS in atrophic acne scars. Dermatol Surg. 2015;41(5):597-604.
4. Kim HJ, Kim TG, Kwon YS, Park JM, Lee JH. Comparison of a 1,550 nm Erbium:glass fractional laser and a chemical reconstruction of skin scars (CROSS) method in the treatment of acne scars: a simultaneous split-face trial. Lasers Surg Med. 2009;41(8):545-549.
5. Dac Thuy LN, Thuy Trang VT, Tran NN, Phuong Thao DT. Comparing the use of 80% trichloroacetic acid and 50% trichloroacetic acid for the treatment of ice pick acne scars. Dermatol Surg. 2024;50(9):847-850.
6. Soysal MÇ, Akçalı C. Comparison of 70% and 100% concentration of trichloroacetic acid peeling efficacy with chemical reconstruction of skin scars technique in atrophic acne scar treatment. Arch Dermatol Res. 2025;317(1):547.
7. Stratman S, He H. The use of chemical reconstruction of skin scars (CROSS) method with trichloroacetic acid (TCA) for atrophic scars: a comprehensive review on application techniques, adjunct therapies, and complications. J Clin Aesthet Dermatol. 2026;19(6):52-67.

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