Unit 3 · Fractional laser & radiofrequency
Two ways to protect the epidermis while still remodelling the dermis beneath it
Fractional delivery and radiofrequency solve the same problem — heating tissue deeply enough to stimulate remodelling without unacceptable downtime — through entirely different mechanisms. This unit works through how fractional photothermolysis spares surrounding skin, then how radiofrequency heats tissue without needing a chromophore at all.
Learn · Fractional laser technology
Treating a fraction of the skin to heal all of it faster
Fractional photothermolysis, introduced by Manstein et al. in 2004, changed the risk–benefit profile of laser resurfacing by replacing confluent tissue treatment with an array of discrete microscopic treatment zones (MTZs). By treating only a fraction of the skin surface per session, the untreated skin between MTZs acts as a reservoir of viable cells that rapidly repopulates the treated columns — accelerating healing while preserving cumulative collagen stimulation.
| Parameter | Ablative fractional (AFR) | Non-ablative fractional (NAFR) |
|---|---|---|
| Mechanism | Microscopic ablative columns through the epidermis into the dermis, with an RTD zone around each column. Epidermis is disrupted. | Microscopic coagulative zones within the dermis. Epidermis is intact but heated — no ablation. |
| Common wavelengths | CO₂ 10,600 nm; Er:YAG 2940 nm fractional modes. | 1440, 1540, 1550, 1927 nm. |
| Treatment fraction | Typically 10–40% surface area per session. | Typically 15–50% surface area per session, density adjustable. |
| Depth of effect | Epidermis to 1–4 mm reticular dermis, parameter-dependent. | 0.4–1.5 mm mid-dermis, parameter-dependent; epidermis relatively spared. |
| Downtime | 3–7 days re-epithelialisation; 1–4 weeks erythema. | 1–3 days erythema and oedema; micro-exfoliation over 3–7 days. |
| Clinical applications | Deep rhytids, acne scarring, significant skin laxity, photodamage reversal, surgical scars. | Mild-to-moderate rhytids, tone and texture, early photodamage, maintenance, periorbital and neck with adjustment. |
| Session frequency | 1–3 sessions, higher per-session efficacy. | 3–6 sessions, lower per-session efficacy, cumulative benefit. |
Predict · Density and depth
Why a conservative practitioner sometimes turns both dials down
Fractional treatment has two independent variables: treatment density (the percentage of surface area treated per session) and treatment depth (how far each MTZ extends into the dermis). Increasing either one increases the collagen stimulus. Before reading on, predict why a practitioner treating a sensitive area such as the neck would deliberately reduce both, even though that lowers the stimulus per session.
Higher density and greater depth both increase collagen stimulus per session, yet a conservative protocol for the neck or periorbital area often reduces both. What is being traded for what?
Hold your answer before you open this. The value is in having reasoned through the trade-off first.
Increasing density reduces the untreated reservoir of viable cells between MTZs, which raises downtime and adverse event risk. Increasing depth reaches further into the dermis for structural improvement, but also increases risk in thinner-skinned or higher-risk regions. Reducing both trades per-session efficacy for reduced downtime and risk, with results accumulated over multiple sessions instead of maximised in one.
A conservative approach for the neck or periorbital area typically sits at a density of around 8–15%, with reduced depth, precisely for this reason.
A patient wants improvement in deep rhytids and acne scarring, and can tolerate a 5–7 day re-epithelialisation window in exchange for fewer overall sessions. Based on the difference in epidermal disruption between ablative and non-ablative fractional delivery, the better-matched option is:
Select an option to commit. The reasoning appears afterwards.
Ablative fractional delivery creates microscopic ablative columns through the epidermis into the dermis, reaching 1–4 mm depending on parameters — appropriate for deep rhytids, acne scarring and significant skin laxity. Its higher per-session efficacy typically requires only 1–3 sessions, against a downtime of 3–7 days for re-epithelialisation.
Non-ablative fractional delivery spares the epidermis and reaches a shallower 0.4–1.5 mm, which suits mild-to-moderate concerns and lower downtime tolerance, but needs 3–6 sessions to accumulate an equivalent benefit — the opposite trade-off to what this patient has stated.
Predict · Chromophore-independent heating
Why radiofrequency does not care about Fitzpatrick skin type
Radiofrequency (RF) devices use alternating electrical current at 0.3–10 MHz to generate heat within tissue via dielectric heating — also called resistive or Joule heating. Unlike laser, RF does not rely on a chromophore. Before reading on, predict why melanin content would be irrelevant to how much heat an RF device generates.
Every laser wavelength in this module has been chosen around what it is absorbed by. RF works equally well across all Fitzpatrick phototypes. What is RF heating tissue with, if not a light-absorbing molecule?
Hold your answer before you open this. The value is in having reasoned through the mechanism first.
When the alternating current of an RF device passes through tissue, it causes oscillation of water molecules and charged ions as they attempt to follow the alternating electric field. This molecular friction generates heat directly — based on the tissue's electrical impedance, not on how much light a particular molecule absorbs. Because melanin is not part of this pathway at all, RF is equally effective across all skin phototypes.
The depth and distribution of that heat is instead determined by the RF device type, electrode geometry, and the impedance characteristics of the target tissue — the variables covered in the device table below.
Collagen fibres denature — partially "melt" — at 60–70°C. This denaturation causes immediate collagen fibril contraction, which is the tightening effect visible immediately post-treatment. The subsequent biological response — fibroblast stimulation and new collagen synthesis — produces the longer-term remodelling benefit over 3–6 months. RF devices are calibrated to reach these temperatures within the target dermal or subdermal layer while the overlying epidermis is actively cooled throughout treatment.
Radiofrequency devices are described as chromophore-independent. This means RF energy heats tissue by:
Select an option to commit. The reasoning appears afterwards.
RF's alternating current causes water molecules and charged ions to oscillate as they attempt to follow the alternating electric field. That molecular friction generates heat directly from the tissue's electrical impedance — no chromophore is involved at any point in the pathway.
This is why RF is equally effective across all Fitzpatrick phototypes, in direct contrast to every laser and IPL device covered earlier in this module, all of which depend on melanin or oxyhaemoglobin absorption and therefore behave differently across skin types.
Learn · Radiofrequency device types
Electrode configuration decides how deep and how broad
RF devices vary primarily by electrode configuration, which determines both the depth of heating and how confined or diffuse it is across the treated tissue.
| Device type | Electrode configuration | Depth & mechanism | Clinical applications | Key consideration |
|---|---|---|---|---|
| Monopolar RF | Single active electrode; current returns through the body to a distant ground plate. | Broad, deep current path to subdermal fat and SMAS (3–6 mm). | Facial and neck laxity, jawline and jowl improvement, body contouring. | Significant patient discomfort; contraindicated with implanted metal in the treatment field. |
| Bipolar RF | Two electrodes on the handpiece; current confined between them. | Depth ≈ half the electrode spacing — more superficial and localised than monopolar. | Skin texture and early laxity; often combined with other modalities. | Requires consistent skin contact — air gaps cause impedance spikes and hot spots. |
| Fractional RF (microneedling) | Insulated microneedles deliver RF at the needle tips within the dermis. | Programmable depth, typically 0.5–4 mm; epidermal heating minimised by insulation. | Acne scarring, laxity, pore refinement, melasma (chromophore independence is an advantage here). | Risk of grid-pattern PIH in darker skin if settings are too aggressive; test patch recommended. |
| Multi-polar RF | Three or more electrodes; current alternates between pairs in rotation. | More uniform heating across a larger volume; often combined with pulsed electromagnetic fields. | Facial and body tightening, cellulite treatment, maintenance programmes. | Lower per-session energy than monopolar — high comfort, but less dramatic single-session results. |
A patient with significant jawline laxity needs energy delivered to the subdermal fat and SMAS layer, at 3–6 mm depth. Based on electrode configuration and penetration depth, the most appropriate RF device type is:
Select an option to commit. The reasoning appears afterwards.
Monopolar RF passes current from a single active electrode through the body to a distant ground plate, giving it a broad current path that penetrates deeply — to the subdermal fat and SMAS layer, at 3–6 mm. This is precisely the depth and tissue plane significant jawline and jowl laxity requires.
Every other RF configuration in this unit trades that depth for something else: bipolar and fractional RF are confined to more superficial or dermal planes, and multi-polar RF favours uniform, comfortable heating over deep, focal reach. Depth requirement is what should drive the device choice here, not general familiarity with a device.
Unit 3 summary
Clinical takeaways
- Fractional delivery trades confluent treatment for a faster reservoir-driven recovery. Untreated skin between microscopic treatment zones repopulates the treated columns, which is what makes fractional resurfacing recover faster than confluent treatment at an equivalent depth.
- Ablative and non-ablative fractional delivery solve different problems. AFR disrupts the epidermis for deeper, higher-efficacy treatment in fewer sessions; NAFR spares the epidermis for lower downtime at the cost of needing more sessions to accumulate the same benefit.
- Density and depth are independent dials, and both carry a cost. Reducing either trades per-session efficacy for a smaller healing reservoir disruption and lower risk — the basis of conservative protocols in the neck and periorbital area.
- Radiofrequency heats tissue without a chromophore. Dielectric heating from molecular friction is why RF performs consistently across all Fitzpatrick phototypes, and electrode configuration — not wavelength — is what determines how deep and how broad that heat reaches.