What the research shows
What the peel is. The standard medium-depth peel applies Jessner's solution and then 35% TCA, for sun-damaged skin, precancerous spots and fine lines (Monheit 1989). Glycolic acid before TCA gives a similar, consistent depth (Coleman 1994). Freezing the skin with solid carbon dioxide first goes slightly deeper, which helps with scars, and repeated coats of TCA deepen any of these peels (Brody 1989).
What it improves. The peel did most for brown sun spots, rough precancerous spots and skin texture, and least for wrinkles (Humphreys 1996). Around the eyes, a CO2 laser smoothed wrinkles far more than the peel, but redness lasted about two and a half months after the peel against four and a half after the laser (Reed 1997).
Precancerous spots. One peel cleared as many visible spots as three weeks of fluorouracil cream, and most patients preferred the single treatment (Lawrence 1995). Photodynamic therapy cleared more spots than a TCA peel at a year, and only the TCA side scarred, in about 1 patient in 5 (Holzer 2017). Pooled trials found peels cleared fewer spots than fluorouracil or photodynamic therapy (Steeb 2021).
Preparing the skin. Two weeks of tretinoin cream before the peel made the skin heal faster, with no difference in the final look (Hevia 1991).
With a facelift. Surgeons long kept peels and facelifts apart for fear of losing skin. TCA up to 35% applied to lifted skin on the day of a deep plane facelift caused no complications (Dingman 1994), and TCA up to 40% on undermined facelift skin produced a predictable burn without killing the skin, while phenol-croton oil should not be used there (Gonser 2017). On eyelid skin, peel depth rose with TCA strength, and the strengths tested were unlikely to pull the lid down (Dailey 1998).
Darker skin and melasma. Complications rise with peel depth and are more likely in darker skin and after sun exposure (Nikalji 2012). For melasma in darker skin, TCA peels worked better than hydroquinone cream alone, and glycolic acid peels better still (Dorgham 2020). For acne scars in darker skin, about half of patients improved moderately; most had temporary dark patches that cleared within three months (Al-Waiz 2002).
Where surgeons disagree
- Peels for precancerous spots. An early split-face trial found the peel as good as fluorouracil (Lawrence 1995); a later trial and pooled data favor fluorouracil and photodynamic therapy (Holzer 2017, Steeb 2021).
- Glycolic acid or TCA for melasma. Pooled trials favor glycolic acid (Dorgham 2020); a direct comparison in Indian women found them equal, with fewer side effects from glycolic acid (Kumari 2010).
- Tretinoin before the peel. It speeds healing (Hevia 1991) but did not improve the final result when used before and after a 40% peel (Humphreys 1996).
What is new
- Adding monthly microneedling to TCA peels improved melasma more than peels alone (Hofny 2023).
- Pooled data now rank peels below fluorouracil and photodynamic therapy for clearing precancerous spots (Steeb 2021).
What is still unknown
- The best peel protocol for precancerous spots; studies carry a high risk of bias and protocols vary (Steeb 2021).
- How to keep melasma from returning; it came back within three months after either a TCA peel or a laser, and maintenance treatment may be needed (Hong 2012).
Key papers
- Monheit 1989: the Jessner's and TCA medium-depth peel.
- Brody 1989: how peel combinations and coats change depth.
- Hevia 1991: tretinoin before a peel speeds healing.
- Dingman 1994: TCA peel on the day of a deep plane facelift.
- Lawrence 1995: one peel matched fluorouracil for precancerous spots.
- Humphreys 1996: the peel helps spots and texture more than wrinkles.
- Reed 1997: CO2 laser against a peel for eye wrinkles.
- Holzer 2017: photodynamic therapy beat TCA for precancerous spots.
- Dorgham 2020: peels for melasma in darker skin.