Carbon dioxide beats erbium on acne scars, and costs about four days

Design

systematic review and meta-analysis of five comparative clinical studies

Population

130 analysed participants with atrophic acne scars

Primary outcome

clinical response, defined as more than 50% improvement

Effect

erbium versus carbon dioxide relative risk 0.69 (95% CI 0.49 to 0.97); downtime 3.67 days longer with carbon dioxide (95% CI 1.90 to 5.44)

Five comparative studies with 130 analysed participants were pooled to compare fractional carbon dioxide against erbium-based fractional lasers for atrophic acne scars, with clinical response defined as more than 50% improvement. Four contributed to the efficacy analysis.

Erbium lasers were less likely to achieve more than 50% improvement than fractional carbon dioxide, relative risk 0.69 (95% CI 0.49 to 0.97, I²=45.9%). Restricting to randomised studies kept the direction but widened the interval across the null, relative risk 0.76 (95% CI 0.54 to 1.08). Carbon dioxide cost more in tolerability: greater treatment pain, mean difference 1.86 (95% CI 1.33 to 2.39), and longer downtime, mean difference 3.67 days (95% CI 1.90 to 5.44). Post-inflammatory hyperpigmentation did not differ significantly, odds ratio 1.75 (95% CI 0.67 to 4.57), nor did acneiform events.

The practical shape of this is a trade the patient should make, not the dermatologist. Carbon dioxide probably works somewhat better; erbium hurts less and returns the patient to work about four days sooner. For a student before examinations or a bride three weeks out, four days of downtime is the deciding variable, and that conversation is more useful than a claim about superiority.

The pigmentation result deserves a caveat rather than reassurance. A confidence interval from 0.67 to 4.57 in 130 mostly non-Indian participants does not exclude a meaningful difference in Fitzpatrick IV and V skin, which is most of an Indian acne scar clinic.

• Offer the choice on downtime and pain, not on a claim of clear superiority
• Quote about four extra days of recovery for fractional carbon dioxide when planning around work or events
• Do not tell patients with Fitzpatrick IV or V skin that pigmentation risk is equivalent — the data cannot support that
• Test-spot and use conservative settings in darker skin regardless of platform
• Record scar subtype and baseline photographs; pooled response rates hide large differences between rolling, boxcar and ice-pick scars

The statistics, in plain English

The headline relative risk of 0.69 has an upper limit of 0.97, and when only randomised studies are kept the interval runs from 0.54 to 1.08 — crossing 1.0. That means the efficacy advantage is suggested by the whole dataset but not established by its most reliable part. Heterogeneity of 45.9% is moderate: the studies are not measuring quite the same thing, which is what you would expect across different laser platforms and scar definitions. With 130 participants in total, absence of a significant pigmentation difference is weak evidence of no difference.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.