Trichloroacetic acid destroys protein on contact. Painted on skin, it coagulates the proteins in the layers it reaches, which kills that tissue in a controlled way. The body then replaces it. New epidermis grows over within about a week, and the dermis underneath lays down fresh collagen over the following months. That second, slower part is where most of the improvement in texture and fine lines comes from.
Depth is everything, and depth is set by three things: the concentration of the acid, how many coats are applied, and how the skin was prepared beforehand. A degreased face with a week of retinoid use will take a peel deeper than an untouched, oily one at the same concentration.
Providers read depth from the frost — the white film that appears as proteins coagulate. Light, patchy frost means the peel is in the epidermis. An even white frost with a pink background means the upper dermis. A solid, opaque white frost means deeper still, and at that point the operator should stop. This is not a decorative detail. Frost is the only real-time feedback available, which is why an experienced set of eyes matters more here than on almost any other peel.
Unlike glycolic acid, TCA is self-neutralizing. It stops when it has used itself up. There is no rinse that halts it partway, which is the reason it is applied slowly and read carefully rather than slapped on and timed.
Get a real depth conversation. Ask directly: what concentration, how many coats, and what depth are you aiming for. A provider who cannot answer that precisely is not the person to do a medium peel on you.
Prime the skin. Most protocols use four to six weeks of a retinoid such as tretinoin, often with a pigment-suppressing agent like hydroquinone, before a medium peel. Priming makes the peel penetrate more evenly and lowers the chance of blotchy pigment afterwards. On brown and Black skin this step is not optional.
Stop the retinoid and any exfoliating acids about five to seven days before the peel itself.
Start antiviral tablets if you have ever had a cold sore. For a medium peel most providers prescribe them regardless of history, because a herpes outbreak on freshly peeled skin can scar.
Clear the calendar honestly. For a medium peel, plan on seven to ten days out of sight and three to four weeks before you look normal in photographs.
Arrange the supplies you were told to buy — bland ointment, gentle cleanser, mineral sunscreen — before the day, not on day two when your face hurts.
Arrive with clean, product-free skin.
Eat beforehand and bring someone to drive you if you are having sedation or oral pain relief for a medium peel.
Expect the provider to degrease your skin hard with acetone. It feels excessive. It is what makes the peel even.
Say something if you have had a recent laser treatment, waxing, or any procedure on the area in the last two weeks.
Your skin is cleaned and then degreased thoroughly with alcohol or acetone. This step takes several minutes and determines how evenly everything that follows lands.
Petroleum jelly is placed at the eye corners, nostril creases and lip line to stop acid pooling in the folds.
For a medium peel, a base layer — Jessner solution or strong glycolic acid — may go on first.
The TCA is applied with gauze or cotton tips, one area at a time: forehead, then each cheek, then nose, then around the mouth. The provider waits and watches between areas.
The burn is real. For a light peel it is a strong sting for thirty to sixty seconds per area, then it fades. For a medium peel it is a serious burning that peaks at around a minute and takes several minutes to settle. Cold air from a fan is the main relief, and it helps genuinely. Numbing cream is of limited use because the acid works below where it reaches, but oral pain relief or light sedation is common for full-face medium peels.
You watch your skin turn white. Frosting appears within thirty seconds to two minutes and looks alarming the first time. It is expected and it is how the provider knows where they are.
Cool saline compresses go on afterwards, which is a substantial relief.
A light peel takes about fifteen to twenty minutes. A full-face medium peel takes thirty to forty-five minutes including waiting between areas.
Throughout: keep the skin covered in a bland ointment or occlusive balm — dry crust cracks and cracked crust scars. Do not pick, do not pull, do not scrub, do not "help" the peeling along. Wash gently with plain water or a mild cleanser. No sun at all, not even through a car window, and mineral sunscreen every day from the moment the skin is intact enough to tolerate it.
TCA is sold online in concentrations from 10 to 100 percent, marketed for home use. Do not. This is one of the few places on this site where the answer is a flat no rather than a qualified one.
The reason is that TCA gives no warning before it goes too deep. There is no rinse that stops it. The only guide to depth is reading frost in real time, which takes training and experience, and by the time an untrained person realizes a spot has gone too far, it already has. Home TCA burns are a recurring cause of permanent scars and permanent pale patches, particularly on the neck and around the eyes, and they are not repairable.
Dotting high-strength TCA into individual scars — the CROSS technique — is even more commonly attempted at home and is worse, because the concentrations involved are 65 to 100 percent and a slip enlarges the scar you were treating.
What is reasonable at home: a leave-on glycolic acid, lactic acid or salicylic acid product, and a retinoid. Used steadily these deliver a decent share of what a light TCA peel offers, spread over months. Nothing sold for home use approaches a medium peel, and nothing should.