In ultrasound therapy, frequency acts as a precise depth control mechanism that determines where energy is delivered within the skin. Specifically, a lower frequency like 4MHz allows energy to penetrate deeply to target foundational muscle layers, while a higher frequency like 7MHz concentrates energy in the more superficial dermal layers.
The Core Takeaway The true efficacy of modern ultrasound therapy lies in multi-layered stimulation. By utilizing different frequencies, practitioners can bypass the skin’s surface to simultaneously target the deep foundation (SMAS) and the upper dermis, creating a comprehensive "sandwich" effect of collagen regeneration that single-depth treatments cannot achieve.
The Physics of Penetration Depth
The Inverse Relationship
There is a fundamental rule in ultrasound physics: frequency is inversely related to penetration depth.
Low Frequency (4MHz)
A 4MHz frequency is designed to travel further into the tissue with less attenuation. This allows the energy to bypass the upper skin layers and impact the deep dermis and the SMAS (Superficial Muscular Aponeurotic System) layer.
High Frequency (7MHz)
Conversely, a 7MHz frequency is absorbed more quickly by tissue. This restricts the energy to the superficial dermis, focusing the thermal effect on the layers closer to the surface where fine lines occur.
Targeting Specific Tissue Layers
Anchoring the Structure
The primary goal of using a lower frequency (4MHz) is structural lifting. By delivering thermal energy to the SMAS layer—the same layer surgeons tighten during a facelift—the treatment creates thermal coagulation points that tighten the skin's structural foundation.
Refining the Surface
The higher frequency (7MHz) addresses the quality of the skin itself. By heating the superficial dermis, this frequency stimulates the contraction of existing collagen fibers and triggers the production of new collagen to smooth out texture and fine lines.
Comprehensive Regeneration
The primary reference highlights that effective treatment is not about choosing one depth over another. It is about a combined treatment protocol that stimulates regeneration across all tissue depths simultaneously.
Understanding the Trade-offs
Depth vs. Precision
While deeper penetration (4MHz) offers dramatic lifting effects, it requires high precision. The energy must be focused exactly on the SMAS layer to avoid affecting underlying structures inappropriately.
Sensation and Comfort
Treatments involving deeper frequencies often result in more intense sensations. Because the energy affects the fibromuscular layer, the patient may feel a deeper ache compared to the superficial heat sensation of higher frequencies.
Variable Recovery
Although non-invasive, multi-layered treatments deliver significant energy. While there is generally no downtime, the comprehensive nature of treating both deep and superficial layers can result in temporary, mild tenderness that single-layer treatments might not induce.
Making the Right Choice for Your Goal
To maximize facial rejuvenation, the specific frequency used should align with the clinical objective.
- If your primary focus is Structural Lifting: The treatment must prioritize lower frequencies (like 4MHz) to target the SMAS layer and address deep tissue laxity and contour loss.
- If your primary focus is Dermal Densification: The treatment should utilize higher frequencies (like 7MHz) to target the superficial dermis for improving skin texture and reducing fine wrinkles.
Ultimately, the most effective rejuvenation comes from a protocol that utilizes both frequencies to rebuild the face from the muscle fascia up to the skin surface.
Summary Table:
| Frequency | Target Depth | Tissue Layer | Clinical Objective |
|---|---|---|---|
| 4MHz | Deep | SMAS & Deep Dermis | Structural Lifting & Contouring |
| 7MHz | Superficial | Upper Dermis | Fine Line Reduction & Texture |
| Combined | Multi-Level | Full Thickness | Total Facial Rejuvenation |
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References
- Ana Cristyna Saad Murad, Fernanda Soubhia Liedtke. Collagen biostimulation in skin aesthetics with micro-focused ultrasound in the presence or absence of calcium hydroxyapatite and poly-L-latic acid: a concise systematic review. DOI: 10.54448/mdnt22306
This article is also based on technical information from Belislaser Knowledge Base .
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