Skin Impedance: Why Medium Frequency Feels Better and Reaches Deeper？

To understand the advantage of medium-frequency stimulation, one has to start with skin impedance. The outermost layer of the skin, the stratum corneum, is composed largely of dry, dead cells surrounded by lipids, and it behaves electrically like a capacitor: the higher the frequency, the lower the impedance. In practical measurements, skin impedance at 50 Hz is on the order of 3,000 ohms or more, while at 4,000 Hz it drops sharply to roughly 40–50 ohms — an eighty-fold difference. That number directly determines both sensation and effectiveness. High impedance means higher voltage is needed to push enough current into the body, and it also tends to bring a sharper stinging or surface-burning sensation; meanwhile, a large share of the energy is dissipated at the skin surface, leaving less current available to reach deeper structures. Low impedance, by contrast, lets the current flow in with less voltage, a milder feel, and deeper reach. This is the fundamental reason medium-frequency currents such as interferential current outperform low-frequency currents in both comfort and depth. Using medium frequency to cross the skin is like opening a door first — the current enters easily, and then performs its fine-grained low-frequency work inside the body. For the user, the immediate experience is less surface irritation, a more pleasant session, and more complete coverage of the area. This principle also sets requirements for electrode design. For current to enter the skin efficiently and evenly, the electrode must maintain stable, full contact with the skin; poor contact concentrates current density in small spots, causing stinging or "hot spots." A well-designed device therefore does not only optimize frequency — it also carefully engineers the contact surface, so that the advantage of low impedance is actually realized. For modern wearable devices, this principle matters even more. A device meant to be used regularly at home must feel comfortable enough to wear, yet it must also reach deep structures in the shoulder, knee, or lower back to be genuinely useful. Applying the impedance characteristics of medium frequency, together with a stable contact design, is precisely the way to satisfy both goals at once. At bottom, the principle of skin impedance reveals a simple truth: the body's outer barrier is not insurmountable — it just needs the right approach. What medium-frequency current does is to borrow a path along the skin's own physical properties rather than fight against them. That is both the technical elegance and the source of its gentle, comfortable feel. In the end, the story of skin impedance is a reminder that good design follows physics rather than fighting it. The body has a natural barrier, and the smartest devices do not try to overpower it — they work with it, choosing frequencies and contact surfaces that let the current flow where it is wanted. That is why medium-frequency stimulation feels effortless: not because the current is weaker, but because it is traveling a path the skin was already willing to let it take.