Acne Scar Treatment by Type: Improvement Rates for Subcision, Fractional Laser, and Microneedling RF

Scars left behind after acne clears up respond to treatment differently depending on their type. Narrow, deeply pitted marks and broad, gently sloping depressions form for different reasons, so even the same laser can produce very different results on each. That is why treating scars usually starts with identifying the type before choosing the right approach, rather than relying on a single procedure to do everything. The main options are subcision, fractional CO2, microneedling RF, TCA CROSS, and HA filler, and each one is best suited to a particular kind of scar. This article breaks down the three scar types, icepick, boxcar, and rolling, and explains which treatment fits each one and why, along with the improvement rates and downtime backed by clinical research. It also covers the pigmentation risk that matters most for Korean skin.

Scar Type	Key Feature	First-Line Treatment	Evidence	Downtime
Icepick	Narrow, deep pinpoint mark	TCA CROSS	80% saw over 70% improvement after 4 sessions of 100% TCA	5-7 days
Boxcar	Sharply defined, angular depression	Fractional CO2 / microneedling RF	Responds well to fractional thermal injury	RF 1-3 days, CO2 5-10 days
Rolling	Broad, gently undulating, caused by fibrous tethering	Subcision, then filler or energy device	44.3% alone, 68.6% with CO2 combined	3-7 days

What Type of Scar Do I Have?

Atrophic acne scars fall into three types based on shape: icepick, boxcar, and rolling. Most people have a mix of types on the same face, so in real-world practice, the standard approach is to identify each type present and combine treatments accordingly.

Icepick scars are narrow, under 2mm wide, and pit vertically deep into the dermis. Because the channel is so narrow and deep, resurfacing the surface alone struggles to reach the bottom. Boxcar scars are depressions with sharply defined, angular edges, standing like round or polygonal walls. Rolling scars have a broad, gentle wave-like shape, caused by fibrous bands that tether the scar downward.

Type	Width and Depth	How to Spot It	Best-Fit Approach
Icepick	Under 2mm, deep and vertical	Looks like a narrow, pointed hole	Localized regeneration at the scar base
Boxcar	Shallow or deep, angular walls	Clearly defined edges	Even remodeling of walls and base
Rolling	Broad and gentle, tethered	Shows up as waviness under light	Releasing the tethering bands

In practice, the difference in response by type is clear. A study using a non-ablative 1550nm fractional laser found improvement rates of 59.2% for boxcar scars, 40.6% for rolling, and only 19.1% for icepick. That means laser alone has real limits for icepick scars. When multiple types are mixed on the same face, the evidence supports a staged approach: release tethering first, remodel collagen next, and finish with surface and pigment correction.

Why Does Subcision Come First for Rolling Scars?

Rolling scars form when fibrous bands beneath the skin pull the scar downward. A laser that only works on the surface has a hard time releasing that pull. Subcision uses a fine needle or blunt cannula inserted below the dermis to directly cut these tethering bands. Once the tethering releases, the depression lifts, and the small hematoma that forms at the release site helps trigger new collagen production.

The effect has been confirmed with quantitative measures. In a study of 40 patients, subcision alone produced 44.3% improvement. Adding cross-linked HA raised that to 62.3%, and adding fractional CO2 raised it to 68.6%, with combination treatment clearly outperforming subcision alone. The share of patients rated as showing excellent improvement also rose, from 15% with subcision alone to 50% with CO2 combined.

That said, the effect of subcision alone is fairly modest, so it is unrealistic to expect it to erase a scar completely on its own. Sessions are usually spaced about a month apart, up to 3 times. Recovery typically takes 3 to 7 days, with bruising and hematoma being the most common side effects. Redness, swelling, and pain were all lowest when subcision was done alone.

Subcision, then, is the starting point for addressing the actual cause of rolling scars. Releasing the tethering first and then adding filler or an energy device is a well-supported way to boost improvement rates. If a broad, gently sloping depression is your main concern, it makes sense to start with subcision and discuss combination options from there.

How Does TCA CROSS Work on Narrow, Deep Icepick Scars?

Narrow, deep scars like icepick type need a treatment that reaches the very bottom of the channel. TCA CROSS applies a high concentration, 90% to 100%, of trichloroacetic acid to the tip of a wooden toothpick and dabs it precisely onto the scar base only. This coagulates the protein inside the scar, and new epithelium and collagen then fill in the space to close the channel. Its advantage is that it leaves the surrounding normal skin untouched.

The evidence is specific. In a study using 100% TCA in 4 sessions spaced 2 weeks apart, 8 out of 10 patients, or 80%, saw more than 70% improvement. The remaining 2 patients improved by 50% to 70%. For icepick scars, depth is generally reported to shrink by about half over 3 to 6 sessions.

Item	Detail
Method	High-concentration TCA applied only to the scar base
Improvement Rate	80% saw over 70% improvement after 4 sessions
Sessions	3-6, spaced 2 weeks apart
Downtime	5-7 days, localized scabbing

Right after treatment, the applied spot shows a white, frost-like reaction and then scabs over, healing in about a week. In the study above, the only side effects were one case of temporary hypopigmentation and one of hyperpigmentation, with nothing more serious. Because the acid is applied only to a localized spot, the risk of pigmentation spreading over a wide area is relatively low, but given the high concentration, precise, careful application is essential.

For Boxcar Scars, How Do Fractional CO2 and Microneedling RF Differ?

Depressions with walls and a floor, like boxcar scars, respond well to treatments that remodel the area evenly through fractional thermal injury. The two main options are fractional CO2 laser and microneedling RF. Results vary somewhat from study to study, so it is hard to call one unconditionally better than the other.

Fractional CO2 creates a grid of microscopic thermal columns that prompts surrounding tissue to weave new collagen. A meta-analysis pooling 8 randomized studies and 249 patients found CO2 came out slightly ahead in scar improvement. On the other hand, split-face studies comparing one side against the other found the two treatments produced essentially equal improvement, with microneedling RF showing faster recovery and fewer pigmentation side effects.

Category	Fractional CO2	Microneedling RF
Efficacy	Slightly ahead in meta-analysis	Equal in split-face studies
Pigmentation Risk	Relatively higher	Lower, spares the epidermis
Downtime	5-10 days, prolonged redness	1-3 days
Sessions	1-3	3-4

Microneedling RF inserts insulated microneedles into the dermis and releases radiofrequency heat only from the needle tips. The key is that it heats only the deep dermis while sparing the epidermis, which is why its pigmentation risk stays low. In the end, CO2 suits people who want a strong effect in fewer sessions and can tolerate a longer recovery, while microneedling RF suits those who want faster recovery and prioritize pigment safety. Rather than one single best treatment, the evidence-based choice depends on your skin condition and how much recovery time you can allow.

How Careful Should Korean Skin Be About Pigmentation?

When choosing a scar treatment, the biggest concern for Korean skin is pigmentation after the procedure. Many Korean patients have medium to darker skin types, and this kind of skin tends to hold onto brown pigment for a long time after strong thermal stimulation. If the scar fades but new pigmentation shows up in its place, satisfaction drops sharply.

The numbers back this up clearly. Fractional CO2 carried a 4.44 times higher risk of pigmentation compared to microneedling RF. On darker skin, that difference is large enough to shape the actual outcome. The pigmentation rate for non-ablative fractional laser is also reported at around 17%, though narrowing the treatment area can help lower that risk.

For this reason, microneedling RF, which spares the epidermis, non-ablative laser, and TCA CROSS, which acts only on a localized spot, are the relatively safer choices for darker skin. Subcision and filler involve little thermal stimulation, so their pigmentation risk is also low. Strong ablative lasers deliver bigger results, but it is worth choosing with the understanding that pigmentation risk grows along with the effect.

Reducing pigmentation risk depends more on care before and after treatment than on the procedure itself. Strict sun protection is essential both before and after, and pretreatment to settle down existing pigment can help when needed. For darker skin in particular, spreading treatment across several gentler sessions rather than going all-in at once is a more realistic way to lower pigmentation risk while still improving the scar.

When Should You Use Filler, and How Do You Combine Treatments?

Filler works by immediately filling the area beneath a depression to restore volume. It suits scars that can be filled directly, like broad rolling scars or shallow boxcar scars, but is not a fit for narrow, deep icepick scars. In a study of 15 patients treated with HA filler, 92% reported improvement, with a clear drop in scar severity and count, and the effect held up for up to 2 years. Large-scale placebo-controlled studies are still limited, though.

Category	HA Filler	PMMA Bellafill
Reversible	Yes, dissolved with hyaluronidase	No, permanent
Duration	Evidence for up to 2 years	Permanent
Best-Fit Scars	Rolling, gentle boxcar	Moderate to severe atrophic

Bellafill, a PMMA-based filler, has FDA approval for moderate to severe atrophic acne scars on the cheeks. Its particles remain in place and encourage the body's own collagen to build around them, which makes the effect permanent. HA filler, by contrast, can be dissolved with hyaluronidase if a problem arises, which makes it easier to manage risk than the non-reversible PMMA option.

The most important thing to understand is that no single treatment erases a scar completely. In most studies, the goal is partial improvement, not total removal. Even a strong combination approach typically achieves about 60% to 70% quantitative improvement, and a single treatment alone falls short of that. That is why multiple sessions and combined treatments are the standard.

In practice, the typical sequence is to release tethering with subcision first, remodel with fractional laser or microneedling RF, and then fill remaining depressions with filler while addressing pigment. Because collagen builds up gradually over weeks to months after treatment, the final result is best judged 3 to 6 months later. Identifying your scar type first, then combining safe treatments step by step, is the most evidence-based way to improve acne scars.