The prevailing interest in non-invasive esthetic treatments to combat aging has led to a vast surge in the use of electrical esthetic devices. Among these popular technologies are microcurrent electrical neuromuscular stimulation (MENS), high-intensity focused ultrasound (HIFU), and radio frequency (RF), which are specifically designed to transmit energy into biological tissue to bring about physiological changes.
Log in to view the full article
The prevailing interest in non-invasive esthetic treatments to combat aging has led to a vast surge in the use of electrical esthetic devices. Among these popular technologies are microcurrent electrical neuromuscular stimulation (MENS), high-intensity focused ultrasound (HIFU), and radio frequency (RF), which are specifically designed to transmit energy into biological tissue to bring about physiological changes.
Energy and Tissue
The skin serves as a barrier against external energy sources, and over 99% of the body's resistance to electrical current comes from the skin's surface. The structure, thickness, and tissue density of the skin can affect how much energy is transferred to underlying tissue, and the skin's response to electrotherapy depends on its properties. Various factors, such as transepidermal water loss, age, medications, nutrient deficiencies, and internal dehydration, can affect the skin's conductivity. Electrical impulses in the body are vital for life and are responsible for functions such as our heartbeat, muscular activity, and nervous system functions, originating in cells.
In the article "Evidences for Biofield," Dr. Igor Jerman notes that every living cell has an electric field of high intensity ranging from 107 V/M (volts to millivolts) to a low intensity below 70 mV (millivolts). When utilizing esthetic devices for facial or body treatments, it is crucial to consider that the human body can produce electricity and contribute to an overall electrical “field” between the body and the device.1
Biological tissue interacts with static and alternating electromagnetic fields across a wide range of frequencies. Static fields are low-energy fields that arise from electrical charges. An electric field is formed when electrical charges exert forces on each other, with like charges repelling each other and opposite charges attracting each other. The combination of iontophoresis and electro-osmosis is termed electrophoresis. The electrical field created allows for the transport of products.2
Human tissue responds differently to electromagnetic fields and various forms of electrotherapy. This response depends on factors such as the type of tissue and the cell's molecular composition. Additionally, the tissue's reaction is influenced by various characteristics of the electromagnetic field, including frequency, intensity, modulation, polarization, pulsing mode, instantaneous and average power, and total absorbed energy. Evidence shows that the electromagnetic properties of tissue change dynamically due to its natural activity, which impacts how biological objects respond to externally applied electromagnetic radiation.
According to Ohm’s Law, the amount of current passing through tissue is determined by the voltage and the tissue's resistance. When using an electrical device, it's important to understand that the current first passes through the electrode, then travels through a gel or other medium, enters the tissue, and finally returns to the electrode. In electrophysiology, the Arndt-Schultz principle applies to all forms of electrical current, including esthetic devices. The physiological response is influenced by the amount of current used. Lower currents can stimulate physiological activity, but the specific effect depends on the type of current. Moderate levels of current can inhibit physiological activity, while strong currents can cause muscle wasting, discomfort, skin burns and depletion of ATP. Furthermore, when the voltage reaches 500 volts or more, the skin's resistance decreases, making the body more susceptible to current flow. The effectiveness of electrotherapy depends on factors such as current type, intensity, conductance, and the size and type of electrodes used.3,4,5
In cellular physiology, electrical impulses respond to various frequencies. Current can be applied to provide sufficient energy to alter cell behavior, while smaller currents are used to stimulate membrane activity, leading to cellular enhancement. Physiologically, stimulated cells carry out important activities as they trigger biological activities in the body. Although cells are electrically neutral, they have a negative charge inside and a positive charge outside. There are high concentrations of potassium ions inside the cell, and cell membranes favor permeability to potassium ions. While sodium ions inside a cell are at a low level, the concentration outside the cells is higher. A sodium-potassium pump in the cell membrane expends energy to maintain this imbalance.
The cell membrane is crucial for generating electromagnetic phenomena by separating charged particles to create a voltage, known as action potential. This separation occurs between electrically charged molecules, resulting in a difference between the two sides of the membrane and creating an electric potential. The stored energy, referred to as resting membrane potential, is facilitated by the imbalance of electrical polarization. The cell membrane effectively manages this energy by utilizing ions with positive charges, such as sodium, potassium, calcium, and hydrogen, as well as ions with negative charges, such as chloride, bicarbonate, and phosphates. This highly functional cell membrane allows electrical transmissions of force to cross the membrane, resulting in high intensity. The separation of charges is subtle, leading to low voltage, but it is enough to create potential energy. It should be noted that the body responds to low levels of current and human tissue does not require intense amounts of electrical energy for a device to “work”.
Electrotherapy is most effective when:
1. The nature of the concern is confirmed;
2. The physiological changes necessary to create improvement or effect are determined;
3) The most appropriate modality or device is selected;
4) An extended treatment plan is determined. It is essential to have a care plan with specific milestones to measure treatment success, and when practical work may need to be replicated.5
Sensory Responses
The skin's sensitivity to pressure and temperature varies from person to person due to factors such as dermis density, blood flow, circulation and hypothalamus function. Subcutaneous tissues, especially fat, can insulate muscle tissues against cold and heat, leading to individual variations in the body's response to treatments. Nerve terminals throughout the body are associated with receptors that sense sensory input. The brain reacts to these signals, resulting in responses in the skin.
There are three types of receptors: thermoreceptors (for heat and cold), nociceptors (for pain) and mechanoreceptors (for mechanical changes or pressure). These receptors transmit external signals to the spinal cord and then to the brain. Sensory nerves are distributed throughout the skin and subcutaneous layer, with the most sensitive receptor sites for temperature being the face, cheeks and lips. Most nerve fibers and endings are in the mid-dermis and papillary dermis. In the epidermis, sensory nerves are connected to keratinocytes, melanocytes, Langerhans cells and Merkel cells.
The epidermal nerves consist of free nerve endings, while the dermis contains free sensory nerve endings and various corpuscles. Peripheral sensory nerves can be classified based on the velocity at which action potentials travel through nerve fibers, such as Aα (alpha) fibers, Aβ (beta) fibers, Aδ (gamma) fibers and C fibers. Aβ and Aδ fibers are primarily sensitive to mechanical stimuli. The skin's nerves include a subset of sensory nerves that are responsive to both mechanical and heat stimuli, known as C fibers. C fibers are the predominant nerve pathway for detecting warmth, while Aδ fibers respond to gentle cooling. Selective C fibers become activated during exposure to extreme cold. It has been discovered through research that there is a connection between the trigeminal nerves and the innervation of facial muscles. Clients with trigeminal neuralgia may experience pain in the sensory territory of the trigeminal nerve due to nerve compression, which can also affect other facial nerves. Symptoms of trigeminal neuralgia can include a burning sensation or sudden shock-like pain that may last for several minutes.5,6,7,8
1. Microcurrent
Microcurrent (MENS) is a low-level, bipolar, alternating, and sub-sensory current, applied at less than 500 microamperes, which mimics the body's own biological current. This current can stimulate physiochemical reactions at the cellular level, activating ATP, collagen and elastin production. As a bioelectric current, it uniquely resonates with the human body and has dielectric properties with the skin. The micro-sized pulsating current aligns with energy channels, circulation, nerve pathways and the lymphatic network. Microcurrent devices use specific electrical frequencies and waveforms to increase cellular metabolism and work internally on muscle fibers and tissues. These frequencies can be aligned to muscle groups and reflex points, along with specific anatomical placement of probes. Applying the current to corresponding muscular regions encourages the "re-education" of distended muscles and assists in revitalizing habitual muscle patterns and atrophy due to the natural aging process and other external and internal influences. Muscle contracture requires ATP, and active muscles require a great deal of energy supported by oxygenation and nutrients. Microcurrents can increase protein and DNA synthesis.
The health of muscles depends on adequate nerve and blood supply. One of the main factors that affect compromised blood flow is the lack of oxygen in the capillary beds, leading to impaired basement membrane function. Without proper blood flow, oxygen and nutrients cannot reach tissues, and waste products of metabolism cannot be removed. Using microcurrent at recommended frequencies can effectively stimulate muscles, causing contraction and relaxation cycles to promote blood circulation. Muscles act as clearing stations for metabolic waste, which can be improved through muscular movement, electrostimulation and increased water intake. Muscles respond well to electrostimulation in small intervals and doses. Microcurrent technology mimics the electrical impulses from the brain and stimulates the Golgi tendon in the muscle, reinforcing its strength and providing definition.9
- Microcurrent range: Direct, pulsed: 300-500 microamps & a range of 20- 300 Hz for vascular and lymphatic stimulation.
- Increased peripheral blood circulation
- Vaso dilation improved venous function
- Improves vascular tone
- Stimulates angiogenesis
- Reduces inflammation
- Reduces edema
- Facilitation of lymphatic movement
- Increase protein synthesis, gluconeogenesis
- Improves cell metabolism and tissue repair5
Contraindications include pacemakers, metal plates, epilepsy, thrombosis, cancer, immunotherapy, chemotherapy, radiation, facial implants, and metal screws or pins.
2. Ultrasonic and Cavitation
The medical field uses ultrasound at frequencies ranging from 2 to 15 MHz to detect anomalies in the body and visualize subcutaneous body structures. "Ultrasonic" refers to anything above audible sound, specifically frequencies over 20,000 Hz. Ultrasonic devices produce sound waves driven by an internal pressure force and should not be compared to other esthetic modalities, as they heat tissues by sound waves rather than by current impulse.
Ultrasonic esthetic skin devices typically operate at frequencies between 1 to 3 MHz and with duty cycles ranging from 20% to 100%. The duty cycle is the ratio between the pulse and the waveform of the electrical output. Duty cycles less than 100% are called continuous and are pulsed to protect the skin from becoming overheated. When the handpiece makes contact, sound waves propagate to stimulate various biochemical effects to assist in product penetration when using the round handpiece or spatula blade.
Cavitation with the spatula blade aims to provide ultrasonic exfoliation; however, due to the diameter of the spatula edge, sonophoresis is limited. Cavitation exfoliation is achieved by the applied water concentration on the skin's surface, the angle at which the spatula blade is held, the frequency range, and the heat generated by the spatula. The primary cleansing mechanism involves the "collapse" of the cavitation water through heat and oscillation, resulting in tiny breaks through the corneocytes and the enlargement of intercellular spaces. The depth of product ionization is determined by probe size and the frequency, with lower frequencies enabling greater penetration depth and higher frequencies facilitating less penetration depth. Low-intensity ultrasonic treatment alters cell permeability and helps re-absorb interstitial fluid. Additionally, it may cause a four-degree rise in core tissue temperature, leading to increased metabolic activity in the cells. Using ultrasound at 2 MHz and 1.5 watts per square inch for five minutes will increase the temperature by three degrees, aiding in oxygenation, phagocytosis, and the transport of cell wastes for removal. Additional frequencies: I MHz 1 million reps/sec 40 MM into tissue for the body, 2MHZ 2 million reps/sec 10-12 MM depth (facial tissue), 3 MHZ 3 million reps/sec 3-5 MM depth (facial tissue and hypertrophic scars).
Sonophoresis significantly enhances the absorption of topical compounds and serums by using sound waves to stimulate micro-vibrations and increase the kinetic energy of molecules within these agents. The level of ultrasonic intensity and the timing of application determines the amount of heat generated. Therefore, it is important to carefully consider the product ingredients to avoid significant molecular changes or degradation. Avoid using the following ingredients with sonophoresis: AHAs, sulfur, masks, acne products, alcohol-based products, and any ingredient that could cause dryness or potential skin irritation when exposed to heat or friction. After treatment, you can use a spatula or sound head to help with the absorption of products.5,10
Contraindications include pregnancy, metal implants (near the face), facial piercings, bone diseases, oral blood thinners, skin cancer, moles, sensitive teeth and dental implants, recent cataract surgery, Retin-A, Differin, pacemaker, frail skin, active pustule acne, recent laser surgery or chemical peel. Do not use over the thyroid, carotid artery, over Botox or fillers received within 10 days.
3. High-Intensity Focused Ultrasound (HIFU)
The HIFU technique is used for facial rejuvenation, lifting, tightening and body contouring. It works by facilitating cellular damage and reducing volume in the target area through the coagulation process. HIFU involves the direct energy of targeted tissue using ultrasound, combined with an additional delivery of focused ultrasound energy. This application has been shown to create precise micro-coagulation zones from the deep dermis to the superficial musculoaponeurotic system (SMAS) and lead to gradual skin tightening through collagen contraction and remodeling. This is achieved by creating microthermal lesions with high-frequency ultrasound beams at the specific tissue site without damaging the epidermis and adjacent tissues. Unlike other thermal technologies, ultrasound frequencies offer low, but adequate amounts of energy that can reach the necessary tissue depth. Frequencies near 4–7 MHz have been found to be most useful for heat deposition, frequencies as low as 0.5 MHz for deep treatments, and frequencies as high as 10 MHz being used for skin treatments.
The optimal choice of focused ultrasound frequency is both application and technique-specific and exemplifies a balance between the desired treatment depth and the rate of heating. The total dose of focused ultrasound energy and the amount of time required to deliver the total dose of energy can be adjusted to achieve anticipated results. The ability to alter the delivery of the energy provides the flexibility of the modality. Commonly reported adverse events associated with this include transient discomfort during the treatment session, erythema, edema, and occasional bruising.
Contraindications: Infections or open skin lesions, active severe or cystic acne, implants (eg, pacemakers, defibrillators), metallic implants, treatment directly over keloids, dermal fillers and smoking.10,11
4. Plasma Technology Devices
The use of plasma devices has been growing in popularity in both medical and esthetic practices for a variety of purposes, such as treating acne scarring and achieving aspects of facial rejuvenation. However, there is a significant amount of controversy surrounding the technology, quality, and variety of devices available in the esthetic market. The complex nature of plasma and its components are subject to valid safety concerns. Components of plasma such as UV radiation, ozone, nitrogen oxide, and electrical current already have existing safety standards issued by national regulatory guidelines in the US, Canada and the EU. Manufacturers are to provide certificates of compliance, and users must receive hands-on training, as devices designed to arc on the skin can cause discomfort and burns. There are instances in the esthetic market where devices marketed as plasma devices may actually function as cauterizing instruments, so it is crucial to acquire the accurate technical information before making a purchase.
Plasma is a form of matter that consists of positively charged ions and free electrons in proportions that offer little to no overall electric charge. Plasma devices rely on ionizing the air (ions, electrons and ROS) between the device tip and the skin to create plasma. The potential difference between these two points generates an arc, delivering the energy to the skin causing immediate changes to cell membranes and their sublimation. Sublimation is the process of turning a solid directly into a gas without becoming a liquid first, which prevents thermal damage to surrounding tissue. The clinical impact of plasma devices on the skin depends on factors such as tissue mechanical and electrical resistance, as well as the potential difference between the device tip and the skin.
Cold plasma technology utilizes oxygen and nitrogen and converts it to non-thermal plasma. Nitrogen plasma devices contain a gas tank and convert medical-grade nitrogen gas into plasma energy. This controlled heating of skin tissue avoids epidermal vaporization and instead focuses on improving the skin's structure, tone, texture and laxity. Neon plasma utilizes electrically charged inert neon gas to create a plasma field, which heats the skin sub-dermally. It produces less heat than nitrogen or oxygen and is similar to nitrogen plasma as it does not cause vaporization.12,13,14
Contraindications: Pregnancy, nursing mothers, metal implants, pacemakers, fever or current infections, cancers, all forms of hepatitis, varicose veins in the area being treated, bone disease, epilepsy, autoimmune disease, diabetes, keloid predisposition, fillers, thread-lift or botulinum toxin in the area being treated, Roaccutane, systemic illness, open wounds, body dysmorphia, allergy to anesthetic agent.
5. Radio Frequency and Heat Tissue Responses
Radiofrequency (RF) utilizes an alternating current to generate thermal energy within the skin by interacting with tissue resistance and is commonly used for tissue tightening. The successful transfer of RF energy relies on various factors, including tissue depth, electrode position, current intensity, application technique and exposure rate. When the current passes through the tissue, ions are drawn to follow the higher-frequency changes, resulting in ionic activity that resists the current flow and produces heat in the tissue.
In a medical spa or physician's office, monopolar devices utilize a single electrode with a grounding pad placed on the patient's body surface. An electric current is produced by the monopolar RF system, which is then transmitted through the skin and into the body, ultimately reaching the grounding electrode. This process heats the dermis to a temperature of 65°C to 75°C without affecting the epidermis. The monopolar RF has a penetration depth of about 20 to 25 mm, which is deeper than that of bipolar or unipolar RF systems.
Monopolar RF devices are commonly used for skin smoothing and tightening. However, due to their deep penetration depth, they may result in more frequent adverse events, such as pain and burning during treatment. Less common adverse reactions include erythema, headache, scarring, edema, fat atrophy and facial palsy.
A unipolar radiofrequency (RF) device has a single electrode and emits RF energy in all directions. It does not have a grounding pad in contact with the patient's body. The penetration depth of unipolar RF ranges from 15 to 20 mm.
Home-use RF devices offer a safer unipolar handpiece, although the power and efficacy are not comparable to those of higher-grade professional models.
The bipolar RF device has two electrodes and no grounding plate with one electrode as the positive pole, while the remaining electrodes serve as negative poles. The penetration depth of bipolar RF is approximately half the distance between the two parallel electrodes, about 2–8 mm.
Multipolar RF devices may also use three electrodes to deliver thermal energy. Bi and Tri polar devices help prevent overheating and tissue damage. Adverse events of bipolar RF therapy are limited to mild erythema and swelling, which usually resolve a few days after treatment. The bipolar contact prongs serve as dual contact points, producing less heat than monopolar devices. Frequencies range from 1 MHz to 6 MHz, with power ranging from 40 W to 240 W. When applying radiofrequency (RF) to the face, it should be limited to 20 minutes, and a dense water-based contact gel should be used before and, if necessary, during the application. To prevent overheating of the skin, a cooling device at 40°F should be applied to the face before and after the session. The skin surface temperature should be maintained at around 100°F (38-40°C) and checked frequently with a digital surface thermometer during the application of each quadrant.
The advantage of using RF to heat tissues, compared to lasers, is that RF at lower frequencies can safely penetrate to a deeper level, helping to improve skin tone and structure and lift tissues. Benefits of RF treatment include promoting local metabolic activity, stimulating dermal collagen, increasing fibroblast activity, firming (with potential impact on both skin and fat), skin tightening, and reducing laxity and wrinkles.5
HSPs in the Skin
There is speculation and concern about the potential for heat from esthetic devices to induce the production of heat shock proteins (HSPs) in the skin. HSPs, also known as stress proteins, occur naturally in the body and are present in all cells of all organisms. Different types of HSPs have varying functions, such as stimulating immune system cells like macrophages and dendritic cells. HSPs help regulate other protein molecules, maintain their structure, and signal the immune system to respond to pathogens or cancerous cells.
Fibroblasts are vital for maintaining the structure of the skin by producing collagen and the extracellular matrix. Under stressful conditions, fibroblasts produce heat shock proteins (HSPs). The presence of HSPs stimulates fibroblasts to multiply by triggering the production of a tissue growth factor called transforming growth factor beta (TGF-β). In addition to fibroblasts, inflammatory cells like neutrophils and macrophages also produce TGF-β. TGF-β affects the proliferation, differentiation, and mobility of fibroblasts. It also encourages increased production of connective tissue growth factor and type 1 collagen.
Collagen can degrade when exposed to specific temperatures, breaking hydrogen bonds within the collagen, resulting in the unwinding of triple helices, and the formation of a gel of random molecules. This leads to changes in tissue tension, shorter fibers, cross-linking, collagen remodeling and new deposition. Collagen contracture happens at different time and temperature combinations rather than occurring at a specific temperature event. Collagen denaturing occurs at temperatures above 149°F (65°C) and is influenced by both heat exposure and tissue hydration levels.
RF energy devices use heat to tighten tissue by relying on Heat Shock Proteins (HSPs). These proteins - HSP27, HSP47, and HSP70, assist in the regeneration of the collagen matrix. HSPs support the survival and replication of skin fibroblasts and aid in the production and assembly of structural components. HSP27 starts working quickly to stabilize cell proteins and prevent cell death. Following collagen deposition, the contraction of the collagen matrix is another key process that occurs after RF treatment. When fibroblast cells were placed in an artificial matrix of collagen and stimulated using platelet-derived growth factor and lysophosphatidic acid, they began to contract the matrix to strengthen it.
Cells that had high levels of HSP27 contracted the matrix more than cells that expressed low levels of HSP27. Fibroblasts overexpressing HSP27 were also better at migration and adhesion. This finding implicates HSP27 to be extremely important for the desired skin-tightening effect of RF therapy. HSP70 increases within the first two days to prevent cells from undergoing programmed cell death and stimulates fibroblasts to produce more HSPs. HSP70 assembles cellular proteins affected by heat treatment and helps determine what to repair and recycle. HSP47 is the collagen assembly protein; its levels rise within two days and continue to increase over the course of 10 weeks. The timeframe of HSP expression after RF treatment explains why clinical results become apparent within 2–4 weeks and then increase in the following months.5, 15,16,17
Contraindications: pregnancy, breastfeeding, active cancer, infections, viral conditions, metal implants, silicone face implants, epilepsy, oral blood thinners, recent fillers or Botox, cataract surgery, bleeding gastrointestinal diseases, chemotherapy, immunotherapy, diabetes, extensive varicose veins, recent IPL/laser, chronic inflammatory diseases, and connective tissue diseases.
Research and Invest Wisely
When incorporating electrotherapeutic devices into facial and body therapy programs, it is crucial to take into account the type and intensity of the energy they deliver, as well as the FDA classification of the device. Before making a purchase, get in touch with the manufacturer of the device to understand its energy parameters and FDA classification.
Investing in professional esthetic equipment that has been carefully researched and sourced, along with conducting comparative cost analyses, is a wise decision. Regardless of the device's size, type, or purpose, choosing quality is essential if you intend to use it frequently and expect it to have longevity, as advised by experienced professionals.
References:
1. https://www.researchgate.net/publication/305469096_EVIDENCES_FOR_BIOFIELD
2. https://www.humanfrequencies.com/electromagnetic-human-field/
3.https://www.bfs.de/EN/topics/emf/lff/introduction/introduction_node.html#:~:text=Constant%20fields%20(static%20or%20stationary,forces%20on%20other%20electric%20charges.
4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763825/
5. https://skininc.texterity.com/skininc/march_2020/MobilePagedArticle.action?articleId=1565497&cmsId=3801206#articleId1565497
6. https://www.sciencedirect.com/science/article/pii/S2352587817300098
7. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4390739/
8. https://www.sciencedirect.com/topics/medicine-and-dentistry/trigeminal-nerve
9. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5385976/
10. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4695420/
11. https://www.dovepress.com/microfocused-ultrasound-for-facial-rejuvenation-current-perspectives-peer-reviewed-fulltext-article-RRFU
12. https://www.thepmfajournal.com/features/features/post/focus-on-plasma-the-application-of-plasma-devices-in-aesthetic-medicine
13. https://www.hmpgloballearningnetwork.com/site/thederm/practice-advances/cold-plasma-dermatology-clinical-uses-and-future-directions
14. https://professionalbeauty.co.uk/site/newsdetails/getting-to-grips-with-the-new-wave-of-plasma-devices
15. https://www.researchgate.net/publication/277668761_Exploring_the_role_of_heat_shock_proteins_in_radiofrequency_energy_therapies
16. https://journals.lww.com/ijdv/fulltext/2022/06000/radiofrequency_in_facial_rejuvenation.6.aspx
17. http://www.americanboardcosmeticsurgery.org/areradiofrequency-treatments-really-safe/
Dr. Erin Madigan-Fleck NMD, LE, LEI is an esteemed figure in the field of dermatological skin sciences, holistic and integrative esthetics and natural health. She is a naturopathic physician, a licensed master cosmetologist-esthetician, an esthetic instructor, and holds a dermatology tech certificate. She serves on the Educational Commission for the International Association of Applied Corneotherapy in Germany and has taught continuing education for over four decades. She is the owner of DemraEducationTV, the Scientific Esthetics Symposium, and her practice Naturophoria, established in 2000.
