Peel Depth: Superficial, Medium, Deep

Peel depth is the single most important variable in peeling, and it is defined histologically — by the deepest skin layer the controlled injury reaches, not by the acid on the label. The three working bands are superficial (epidermis), medium (papillary dermis) and deep (reticular dermis). Each band maps to a predictable set of indications, a predictable downtime, and a predictable risk profile — and you select it deliberately by choosing the agent, its concentration and free acid, the contact time, and how many coats you layer.

The three depth bands

Superficial — epidermis

Superficial peels injure within the epidermis, at most reaching the dermo-epidermal junction. They produce controlled desquamation and accelerated turnover without dermal wounding.

• Indications: dullness and uneven tone, superficial dyschromia and PIH, comedonal/mild inflammatory acne, texture refinement, and priming before deeper work.
• Agents: glycolic 20–70%, lactic 20–40%, mandelic, salicylic 20–30%, low-strength TCA (~10–15%).
• Downtime: roughly 1–3 days of mild flaking or none at all; usually a series of 4–6 sessions.

Medium — papillary dermis

Medium-depth peels destroy the epidermis and wound the papillary dermis, triggering meaningful collagen remodeling.

• Indications: moderate photoaging, epidermal melasma and stubborn PIH, actinic keratoses, mild atrophic acne scarring.
• Agents: TCA ~35%, Jessner's + TCA, glycolic-70%-primed TCA, retinoid/multi-acid combination peels.
• Downtime: roughly 5–7 days with visible exfoliation; typically 1–3 sessions spaced weeks to months apart.

Deep — reticular dermis

Deep peels reach the mid-reticular dermis with substantial tissue destruction and the highest efficacy and risk.

• Indications: severe photoaging, deep rhytides, significant scarring.
• Agents: phenol (Baker-Gordon), high-strength TCA (>50%, now largely superseded for full-face by phenol or laser).
• Downtime: 10–14 days minimum, prolonged erythema for weeks. Generally reserved for Fitzpatrick I–III; phenol requires cardiac monitoring.

How depth is actually controlled

Depth is not a fixed property of an acid — it is something you dial in. Five levers move it:

For metabolic AHAs, depth is dominated by free-acid value, pH and dwell time, and you stop the peel by neutralising. For coagulant TCA, depth is dominated by concentration and coat count, read live off the frost. Layering a keratolytic primer (Jessner's, or a glycolic prep) before TCA breaches the barrier and lets a lower TCA concentration reach medium depth — more control, less peak insult.

Depth selection in skin of color

The depth–risk curve is steeper in Fitzpatrick IV–VI. The same papillary-dermal injury that remodels collagen also risks tipping labile melanocytes into PIH. The practical rule: in darker skin the working window is superficial to carefully-titrated medium, reached with controllable agents (AHAs, mandelic, low-to-mid TCA) on primed skin, building depth across a series rather than chasing it in one aggressive session. Deep peels are generally contraindicated in IV–VI.

Key takeaway

Decide the depth first, then choose the agent and protocol that reach it predictably. Superficial buys safety and maintenance; medium buys remodeling at the cost of downtime; deep buys maximal correction at the cost of risk and is off the table for most darker skin. Every other lesson in Foundations is, in effect, about hitting the depth you intended — and no deeper.