Tissue Impedance and RF Heating Depth: The Physics Behind Frequency Choice

Simplify skin as a circuit: the stratum corneum is a capacitor (insulator), epidermis and dermis a parallel resistor-capacitor, subcutaneous fat a high-impedance layer, muscle and blood (water-rich) low impedance. RF current preferentially follows the lowest-impedance path — the “shunting effect” from which all RF heating models start.

• Low (<1 MHz): cell membranes act as insulators, forcing current through deeper tissue — deep penetration but strong nerve stimulation.
• Mid (1-10 MHz, e.g., 6.78 MHz): balances depth against neuromuscular stimulation thresholds; the mainstream aesthetic range.
• High (>10 MHz): easy capacitive coupling, uniform superficial heating, low stimulation — but energy stays shallow.

• Fat is water-poor and high-impedance — RF crosses it inefficiently, which is why monopolar claims of fascial reach rarely mean deep fat heating.
• Edematous tissue lowers impedance and heats more at equal energy; immediate post-op and one-week strategies should differ.
• Real-time impedance monitoring with automatic energy matching is the watershed feature of high-end systems.

When vendors claim “X cm penetration”, ask for frequency, electrode configuration and measured tissue-model data — not a bare depth number. LEIJEX ships impedance-energy test reports with its systems; see the product center.

Why do results vary so much between people?

Skin thickness, fat thickness and hydration shift energy distribution. Individualized protocols and disciplined course management matter more than brand.

Can RF be used over implants?

Metal concentrates current and heat. Pacemakers, stents and zones near silicone implants are contraindicated or relatively contraindicated — screen before treatment.

• Monopolar RF
• RF Treatment Depth
• Reading Device Parameters