Abstract:
A technique for detecting and providing alerts or indications that can be used for controlling or altering the displacement speed of an applicator coupling skin heating energy across a treated skin. A temperature sensor monitors the rate of skin temperature change and provides feedback related to altering the applicator displacement speed according to the rate of skin temperature change. Disclosed is also an applicator for implementing this method.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is being filed under 35 U.S.C 371 as a national patent application based on International Application Number PCT/IL2009/000856 filed on Sep. 3, 2009 which application claims priority to U.S. Provisional Application 61/095,973 filed on Sep. 11, 2008 and 61/107,744 filed on Oct. 23, 2008, all of which are hereby incorporated by reference. 
    
    
     TECHNOLOGY FIELD 
     The method and apparatus relate to the field of skin treatment and personal cosmetic procedures and, in particular, to safe skin treatment procedures. 
     BACKGROUND 
     External appearance is important to practically everybody. In recent years, methods and apparatuses have been developed for different cosmetic treatments to improve external appearance. Among these are: hair removal, treatment of vascular lesions, wrinkle reduction, collagen destruction, circumference reduction, skin rejuvenation, and others. In these treatments, a volume of skin to be treated is heated to a temperature that is sufficiently high as to perform the treatment and produce one of the desired treatment effects. The treatment temperature is typically in the range of 38-60 degrees Celsius. 
     One method used for heating the epidermal and dermal layers of the skin is pulsed or continuous radio frequency (RF) energy. In this method, electrodes are applied to the skin and an RF voltage, in a continuous or pulse mode, is applied across the electrodes. The properties of the voltage are selected to generate an RF induced current in the skin to be treated. The current heats the skin to the required temperature and causes a desired effect, performing one or more of the listed above treatments. 
     Another method used for heating the epidermal and dermal layers of the skin is illuminating the skin segment to be treated by optical, typically infrared (IR) radiation. In this method, a segment of skin is illuminated by optical radiation in a continuous or pulse mode. The power of the radiation is set to produce a desired skin effect. The IR radiation heats the skin to the required temperature and causes one or more of the desired effects. 
     An additional method used for heating the epidermal and dermal layers of the skin is application of ultrasound energy to the skin. In this method, ultrasound transducers are coupled to the skin and ultrasound energy is applied to the skin between the transducers. The properties of the ultrasound energy are selected to heat a target volume of the skin (usually the volume between the electrodes) to a desired temperature, causing one or more of the desired treatment effects, which may be hair removal, collagen destruction, circumference reduction, skin rejuvenation, and others. 
     Methods exist which simultaneously apply a combination of one or more skin heating techniques to the skin. Because all of the methods alter the skin temperature, monitoring of the temperature is frequently used to control the treatment. In order to continuously monitor skin temperature, suitable sensors such as a thermocouple or a thermistor could be built into the electrodes or transducers through which the energy is applied to the skin. Despite the temperature monitoring, certain potential skin damage risks still exist, since the sensor response time depends on heat conductivity from the skin to the sensor and inside the sensor, and may be too long and even damaging to the skin before the sensor reduces or cuts off the skin heating power. To some extent, this risk can be avoided by reducing the cut-off temperature limit operating the sources of optical radiation, RF energy, and ultrasound energy. However, this would limit the RF energy transmitted to the skin and the treatment efficacy. In some instances, for example, when the applicator is static, the temperature of the skin (and of the electrodes) may increase fast enough to cause skin damage. 
     The devices delivering energy to the skin, such as electrodes, transducers and similar are usually packed in a convenient casing, an applicator, operative to be held and moved across the skin. The user has to adjust applicator movement speed to a given constant skin heating energy supply, such as to enable optimal or proper skin treatment. However, at present the user has no indication if the selected applicator speed is proper or not. 
     There is a need to provide a method to alert or signify the user as early as possible of the undesired skin or electrode temperature changes. There is also a need to allow the user to adapt applicator movement speed at constant skin heating energy supply, enabling optimal or proper skin treatment. This is especially important for the fast developing field of personal skin treatment apparatuses enabling their safe use, as the typical user of such apparatus may be inexperienced. 
     BRIEF SUMMARY 
     When heating energy is applied to a segment of skin to be treated and the applicator is displaced from one segment of skin to another, there is a difference in the rate of the skin temperature increase or change, which depends on the speed of displacement of the applicator. When the applicator is moved too quickly, the rate at which the temperature of the skin increases is significantly lower than the rate of temperature increase in the course of “proper” applicator movement speed. A high rate of temperature change is indicative of a static applicator, a condition that may cause burns, blisters and other skin damage. Proper speed of displacement of the applicator may therefore be achieved by controlling the rate of the skin temperature change. 
    
    
     
       BRIEF LIST OF DRAWINGS 
       The apparatus and the method are particularly pointed out and distinctly claimed in the concluding portion of the specification. The apparatus and the method, however, both as to organization and method of operation, may best be understood by reference to the following detailed description when read with the accompanying drawings, in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the method. 
         FIG. 1  is a schematic illustration of an exemplary embodiment of the apparatus for personal skin treatment. 
         FIGS. 2A and 2B , collectively referred to as  FIG. 2 , are schematic illustrations of front and side views of the first exemplary embodiment of the present applicator configured to apply RF energy to a segment of skin. 
         FIG. 3  is a graphic illustration or plot of the skin (and RF electrodes) temperature dependence on the speed of applicator displacement. 
         FIGS. 4A and 4B , collectively referred to as  FIG. 4 , are schematic illustrations of full and insufficient contact of the electrode with a segment of skin. 
         FIG. 5  is an exemplary schematic illustration of the dependence of skin impedance on the quality of electrode-skin contact. 
       FIGS.  6 A- 6 E-are schematic illustrations of some exemplary configurations of the electrodes of the present applicator. 
         FIGS. 7A and 7B  are schematic illustrations of a second exemplary embodiment of the present applicator including a skin temperature probe configured to measure the level of RF energy applied to a segment of skin. 
         FIGS. 8A and 8B , collectively referred to as  FIG. 8 , are schematic illustrations of a third exemplary embodiment of the present applicator configured to apply RF energy and optical radiation to a segment of skin. 
         FIG. 9  is a schematic illustration of a forth exemplary embodiment of the present applicator configured to apply ultrasound energy to a segment of skin. 
         FIG. 10  is a schematic illustration of a fifth exemplary embodiment of the present applicator configured to apply ultrasound energy and optical radiation to a segment of skin. 
         FIG. 11  is a schematic illustration of a sixth exemplary embodiment of the present applicator configured to apply RF energy, ultrasound energy, and optical radiation to a segment of skin. 
         FIG. 12  is a schematic illustration of a seventh exemplary embodiment of the present applicator configured to apply RF energy, ultrasound energy, and optical radiation to a segment of skin formed as a protrusion. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof. This is shown by way of illustration of different embodiments in which the apparatus and method may be practiced. Because components of embodiments of the present apparatus can be in several different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized, and structural or logical changes may be made without departing from the scope of the present method and apparatus. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present apparatus and method is defined by the appended claims. 
     As used herein, the term “skin treatment” includes treatment of various skin layers such as stratum corneum, dermis, epidermis, skin rejuvenation procedures, wrinkle removal, and such procedures as hair removal and collagen shrinking or destruction. 
     The term “skin surface” relates to the most external skin layer, which may be stratum corneum, epidermis, or dermis. 
     As used herein, the term “rate of temperature change” means a change of the skin or electrode temperature measured in temperature units per time unit. 
     The term “skin heating energy” incorporates RF energy, ultrasound energy, optical radiation, and any other form of energy capable of heating the skin. 
     Reference is made to  FIG. 1 , which is a schematic illustration of a first exemplary embodiment of the apparatus for safe skin treatment. Apparatus  100  comprises an applicator  104  operative to slide along a subject skin (not shown), a control unit  108  controlling the operation of apparatus  100 , and a harness  112  connecting between applicator  104  and control unit  108 . Harness  112  enables electric, fluid, and other type of communication between applicator  104  and control unit  108 . 
     Control unit  108  may include a source of skin heating energy  116 . A few non-limiting examples of a source of skin heating energy include an RF energy generator, a source of optical radiation, or a source of ultrasound energy. Control unit  108  may include control electronics that may be implemented as a printed circuit board  120  populated by proper components. Board  120  may be located, together with control unit  108 , in a common packaging  124 . Board  120  may include a feedback loop  128  configured to monitor, during the course of operation, the quality of the skin heating energy applied by the skin coupling, and a feedback loop  132  for monitoring the temperature of a segment of treated skin and deriving there from the rate of temperature change. The term coupling as applied to various probes and devices with skin within this description refers to creating contact with the skin in such a way that energy can be transferred to the skin or measurements can be taken. Apparatus  100  may receive power supply from a regular electric supply network receptacle, or from a rechargeable or conventional battery based supply. 
     Applicator  104  may include one or more RF energy supplying electrodes  140 , visual skin treatment progress indicator  144 , and an audio skin treatment progress indicator  168 . The indicators may be configured to inform or signify to the user the status of interaction of the RF energy with the skin, and alert the user with regards to undesirable applicator displacement speed or RF energy variations. For example, if the applicator displacement speed is slower than the desired or proper displacement speed, an audio process progress indicator will alert or signify the user by way of audio signal. The visual status indicator may be operative to indicate to or alert the user with a signal that the applicator displacement speed is higher than the desired displacement speed. Any other combination of audio and visual process progress indicator operation is possible. 
       FIGS. 2A and 2B  are schematic illustrations of a front view ( FIG. 2A ) and a side view ( FIG. 2B ) of a second exemplary embodiment of the present applicator. Applicator  200  includes a convenient to hold case  204  incorporating one or more electrodes  208  operative to apply safe levels of skin heating energy to a subject skin  212 . The skin heating energy in this particular case is RF energy. A temperature sensor such as, for example, a thermistor or a thermocouple  214  is built into one or more electrodes  208  and is operative to provide the electrode temperature reading to a feedback loop  132  operating an RF energy-setting control circuit, which may be implemented as a printed circuit board  222 . 
     It has been experimentally discovered that the temperature change of (a) the skin segment located between the RF electrodes and (b) the electrodes in contact with the skin at a constant skin heating energy level, depends on the applicator displacement speed.  FIG. 3  graphically illustrates the skin and RF electrodes temperature dependence on the applicator displacement speed. Curve  300  illustrates the rate of temperature change for a static applicator. Curves  304  and  312  illustrate the rate of temperature change as a function of the applicator displacement speed. The applicator displacement speed was respectively 5 cm/sec and 10 cm/sec for curves  304  and  323 . (The graphs are given for a thermistor with a negative temperature coefficient.) Although the present graphs are based on the use of a thermistor, non-limiting examples of other temperature detectors include termocouples, resistance temperature detectors (RTD), and non-contact optical detectors such as a pyrometer and similar devices. The thermistor was selected because it possesses higher precision within a limited temperature range and a faster response time. 
     Referring once again to  FIG. 1  (circuit board  120 ), and  FIGS. 2A and 2B  (control circuit  222 ) include a feedback loop mechanism  132  configured to generate a rate of temperature change based on temperature sensor  214  readings. The rate of temperature change may be measured in degrees (Celsius or any other temperature unit) per time unit. Alternatively, there may be a customized integrated circuit including thermistor  214  and a mechanism of converting temperature into the rate of temperature change. Temperature measurements may be converted into a rate of temperature change using either digital or analog conversion circuits. 
     Heat transfer from the skin to the electrode, and accordingly the temperature measured by the temperature sensor, is largely dependent on the quality of the contact between the electrode and the skin. Differences in the quality of the contact can cause a large variability in the temperature measurement. Firm contact between electrodes  208  and subject skin  212 , as illustrated in  FIG. 4A , supports a short response time of the temperature sensor to the variations in the skin temperature, whereas with poor contact, as illustrated in  FIG. 4B , the response time of the temperature sensor may be much longer. In order to improve the RF electrode contact with the skin, a coupling gel can be applied to skin  212  improving, to some extent, heat transfer and RF energy coupling. The gel, however does not completely resolve the problem or compensate for poor or improper electrode-skin contact. 
     RF energy coupled to the skin induces an electric current that heats the skin. The current is dependent on the skin impedance, which is a function of the quality of the RF electrode contact with the skin.  FIG. 5  is an exemplary graphical illustration of the skin impedance dependency on quality of the electrodes with the skin contact. The temperature measured by the sensor is dependent on the actual rate of heat exchange between the electrode and the skin and on the quality of the electrode with the skin contact. Proper contact between electrodes  208  and skin  212  ( FIGS. 2A and 2B ) may be detected during the treatment by monitoring skin impedance between electrodes  208  as disclosed in the U.S. Pat. No. 6,889,090 awarded to the same assignee as the present disclosure. The impedance measurement is an excellent indicator of the contact quality. Low impedance between electrodes  208  and skin  212  ( FIGS. 2A and 2B ) means that a firm contact between the electrode and the skin exists and accordingly the temperature sensor can follow the changes in the skin temperature sufficiently quick. Other known impedance monitoring methods may also be applied. 
     Generally, it is possible to measure the quality of the thermal contact through monitoring the rate of heating (or temperature change) of the temperature sensor (i.e., good contact results in a higher rate of heating). However, the measurements taken would not provide an actual indication as to whether the rate of heating is indeed rapid or slow, because it may be affected by firm or poor electrode-skin contact. The impedance measurement is independent of the temperature sensor measurements. Thus, continuous impedance monitoring provides electrode-skin contact quality and allows the electrode skin thermal contact influence on the rate of temperature change measurement to be eliminated or normalized. 
     In addressing this issue, control circuit  222  includes a mechanism  128  ( FIG. 2B ) configured to continuously monitor the skin impedance by measuring the electric current between electrodes  140  ( FIG. 1 ) or  208  ( FIGS. 2A and 2B ). Continuous monitoring of the quality of contact of the electrodes with the skin eliminates the influence of the electrode-skin contact on the measurements of the rate of temperature variations making the rate of temperature variations an objective indicator of the skin RF energy interaction and treatment status. Thus, regardless of the quality of the contact between the electrodes and the skin, an indication of the rate of temperature variations normalized in this manner provides quality feedback to the user regarding the operation of the apparatus. 
       FIGS. 6A ,  6 B,  6 C,  6 D and  6 E are schematic illustrations of exemplary configurations of the RF electrodes of the present applicator. Electrodes  604  may be elongated bodies of oval, rectangular or other shapes. In one embodiment ( FIG. 6A ), electrode  604  is a solid electric current conducting body. In another embodiment ( FIG. 6B ), electrode  616  may be a flexible electric current conducting body. A flexible electrode is capable of adapting its shape, shown by phantom line  620 , to the topography of the treated subject skin enabling better contact with the skin. In still a further embodiment, electrode  604  may be a hollow electrode (A hollow electrode generally has a thermal mass smaller than a comparable sized solid electrodes).  FIG. 6C  shows an applicator  624  containing three equi-shaped electrodes  628 .  FIG. 6D  shows an applicator  632  containing a plurality of equi-shaped electrodes  636 . The electrodes may be of round, elliptical, oval, rectangular or other curved shapes, as appropriate for a particular application. The geometry of the electrodes is optimized to heat the skin in the area between the electrodes. 
     The RF electrodes are typically made of copper or nickel coated aluminum or other metals characterized by good heat conductivity. The electrodes have rounded edges in order to avoid hot spots on the skin surface near the edges of the electrodes. Rounded electrode edges also enable smooth displacement of applicator  104  ( FIG. 1 ) or  204  ( FIG. 2 ) across the skin surface.  FIGS. 6A through 6D  illustrate bi-polar electrode systems.  FIG. 6E  illustrates a uni-polar electrode system  640 . Each of the electrodes may contain a temperature sensor  644  configured to measure the electrode temperature in course of operation. Temperature sensor  644  may reside inside the electrode or form a continuous plane with one of it surfaces. For example, in  FIG. 6B , surface  648  forms direct contact with the skin enabling direct skin temperature measurement. 
     Solid metal electrodes  604  may have a relatively large thermal mass and require time until the correct reading of the temperature sensor  644  is established.  FIGS. 7A and 7B  are schematic illustrations of another exemplary embodiment of the present applicator. The temperature sensor  644  may be located in a spring-loaded probe  704  having a small thermal mass, compared to the electrodes, and adapted for sliding movement across the subject skin  212 . Depending on the size of the skin segment treated, there may be one or more probes  704  with each probe  704  incorporating a temperature sensor  644 . Processing of the temperature sensor readings is similar to the processing manner described above and is directed to defining the rate of skin temperature change, or signifying and informing the user of extreme temperature values. Use of a number of probes  704  with each probe  704  incorporating a temperature sensor  644  enables a more accurate temperature measurement and rate of temperature change assessment and a uniform treated skin segment thermal profile mapping. 
     Electrodes  704 , of applicator  700  may be coated with a thin metal layer sufficient for RF energy application, wherein the electrodes themselves may be made of plastic or composite material. Both plastic and composite materials are poor heat conductors and a temperature sensor located in such electrodes would not enable rapid enough temperature reading required for RF energy correction and may not provide a correct reading. The addition of a temperature sensor located in a spring-loaded probe  712  allows rapid temperature monitoring even with plastic electrodes. This simplifies the electrode construction and enables disposal where needed of electrodes  704  for treatment of the next subject, and variation of the shape of the electrodes as appropriate for different skin treatments. In an alternative embodiment, the temperature sensor may be an optical non-contact sensor such as a pyrometer. 
     A coupling gel can be applied to the skin before applying the RF energy, which to some extent, improves heat transfer and RF energy coupling. Accordingly, applicator  700  may include an optional gel dispenser  752  similar or different from gel dispenser  152  ( FIGS. 1 and 2 ). Gel dispenser  752  may be operated manually or automatically. The gel would typically be selected to have an electrical resistance higher than that of the resistance of the skin. In some embodiments a gel reservoir may reside inside control unit  108  ( FIG. 1 ) and be supplied to the skin to be treated with the help of a pump (not shown). 
       FIG. 8  is a schematic illustration of an additional exemplary embodiment of the present applicator. Applicator  800  includes a source of optical radiation  804  located between electrodes  808  and configured to illuminate at least the segment of the skin located between electrodes  808 . The source of optical radiation may be one of a group consisting of incandescent lamps and lamps optimized or doped for emission of red and infrared radiation, and a reflector  820  directing the radiation to the skin, an LED, and a laser diode. The spectrum of optical radiation emitted by the lamps may be in the range of 400 to 2400 nm and the emitted optical energy may be in the range of 100 mW to 20 W. An optical filter  812  may be selected to transmit red and infrared optical radiation in order to transmit a desired radiation wavelength to the skin. Filter  812  may be placed between the skin and the lamp and may serve as a mounting basis for one or more electrodes  808 . Reflector  820  collects and directs radiation emitted by lamp  804  towards a segment of skin to be treated. When LEDs are used as radiation emitting sources, their wavelengths may be selected such as to provide the desired treatment, eliminating the need for a special filter. A single LED with multiple wavelength emitters may also be used. 
     Operation of the source of optical radiation  804  enhances the desired skin effect caused by the RF energy induced current. All electrode structures described above, visual and audio signal indicators are mutatis mutandis applicable to respective elements of applicator  800 . A temperature sensor  828  may be located in one or more electrodes  808  or probes similar to probe  712  ( FIG. 7A ) may be added (not shown) and located so as not to mask optical radiation. A manually or automatically operated gel dispenser  830  similar to gel dispenser  152  ( FIGS. 1 and 2 ) may be part of the applicator  800 . 
       FIG. 9  is a schematic illustration of a forth exemplary embodiment of the present applicator configured to apply ultrasound energy to a segment of the skin formed as a protrusion. Ultrasound energy is another type of skin heating energy. The ultrasound energy is applied to the skin of a subject with the help of an applicator  900 , which may include a conventional ultrasound transducer  904  and one or more temperature probes  908  arranged to provide the temperature of the treated skin section  912 . Transducer  904  may be of a curved or flat shape and configured for convenient displacement over the skin. Lines  916  schematically show skin volume  912  heated by the ultrasound energy/waves. 
       FIG. 10  is a schematic illustration of a fifth exemplary embodiment of the present applicator configured to apply ultrasound energy and optical radiation to a segment of the skin. The ultrasound energy is applied to skin  1012  of a subject with the help of an applicator  1000 , which may include a phased array ultrasound transducer  1004 , one or more temperature probes  1008  arranged to provide the temperature of the treated skin segment  1012 , and one or more optical radiation sources  1016 . Individual elements  1020  forming transducer  1004  may be arranged in a desired order and emit ultrasound energy  1024  to heat the desired depth of skin segment  1012 . Optical radiation sources  1016  may be configured to irradiate the same skin segment  1012  treated by ultrasound, accelerating generation of the desired skin effect. 
       FIG. 11  is a schematic illustration of a sixth exemplary embodiment of the present applicator configured to apply RF energy, ultrasound energy, and optical radiation to a segment of the skin.  FIG. 11  is a top view of an applicator  1100  configured for application to a segment of skin  1112 . Applicator  1100  includes a bell shaped case  1104  and may include one or more ultrasound wave transducers  1120  configured to couple ultrasound energy to skin  1112 , one or more RF energy supplying electrodes  1124 , and one or more sources of optical radiation  1128 . Applicator  1100  further includes one or more temperature probes  1116  similar to the earlier described temperature probes. Ultrasound wave transducers  1120  are configured to cover as large as possible segment of skin  1112 . RF energy supplying electrodes  1124  may be arranged to provide a skin heating current in the direction perpendicular to that of propagation of ultrasound energy. Presence of firm contact of skin  1112  with electrodes  1124  may be detected, for example by measuring the skin impedance. Firm contact of skin  1112  with ultrasound wave transducers  1120  may be detected by measuring the power of reflected ultrasound energy from the skin  1112 . 
       FIG. 12  is a schematic illustration of an eighth exemplary embodiment of the present applicator configured to apply RF energy, ultrasound energy, and optical radiation to a segment of the skin formed as a protrusion. Applicator  1200  is a bell shaped case  1104  with inner segment  1204  containing one or more ultrasound wave transducers  1208 , one or more RF energy supplying electrodes  1212  and optionally one or more sources of optical radiation  1216 . A vacuum pump  1220  is connected to the inner segment  1204  of applicator  1200 . When applicator  1200  is applied to skin  1224 , the inner segment  1204  becomes hermetically closed or at least sufficiently sealed to enable the creation of a temporary vacuum. Operation of vacuum pump  1220  evacuates air from inner segment  1204 . Negative pressure in inner segment  1204  draws skin  1224  into inner segment  1204  forming a skin protrusion  1228 . As skin protrusion  1228  grows, it occupies a larger volume of inner segment  1204 , and spreads in a uniform way inside the segment. The protrusion spreading enables firm contact of skin  1224  with electrodes  1212 . When firm contact between skin protrusion  1228  and electrodes  1212  is established, RF energy is supplied to skin protrusion  1228 . Presence of firm contact of skin  1224  with electrodes  1212  may be detected for example, by measuring the skin protrusion  1224  impedance, as explained hereinabove. 
     Applicator  1200  further includes one or more ultrasound wave transducers  1208  configured to couple ultrasound energy to skin protrusion  1228 . Ultrasound transducers  1208  may be conventional transducers or phased array transducers. 
     Applicator  1200  and other applicators described may contain additional devices supporting skin and electrodes cooling, auxiliary control circuits, wiring, and tubing not shown for the simplicity of explanation. A thermo-electric cooler or a cooling fluid may provide cooling. The cooling fluid pump, which may be placed in a common control unit housing. 
     For skin treatment procedures, the user couples the applicator to a segment of skin, activates one or more sources of skin heating energy and applies the energy to the skin. For example, applying RF energy or ultrasound energy to skin, or irradiating the skin with optical radiation. RF energy interacts with the skin inducing a current in the skin that heats at least the segment located between the electrodes. The heat produces the desired effect on the skin, which may be wrinkle removal, hair removal, collagen shrinking or destruction, and other cosmetic and skin treatments. In order to improve RF to skin coupling the treated skin segment may be first coated by a layer of suitable gel typically having resistance higher than that of the skin. 
     Ultrasound energy causes skin cells mechanical vibrations. Friction between the vibrating cells heats the skin volume located between the transducers and enables the desired treatment effect, which may be body shaping, skin tightening and rejuvenation, collagen treatment, removal of wrinkles and other aesthetic skin treatment effects. 
     Application of optical radiation of proper wavelength to skin causes an increase in skin temperature because the skin absorbs at least some of the radiation. Each of the mentioned skin heating energies may be applied to the skin alone or in any combinations of them to cause the desired skin effect. 
     For skin treatment, the user or operator continuously displaces the applicator across the skin. When the user displaces the applicator at a speed slower than the desired or proper speed, an indicator, such as an audio signal, can be activated to attract the user&#39;s attention and thereby to help avoid or alleviate the risk of potential skin burns. The temperature sensor continuously measures temperature and may shut down RF energy supply when the rate of temperature increase or change is too fast or when the absolute temperature measured exceeds the preset limit. When the user displaces the applicator at a speed higher than the desired or proper speed, the rate of temperature change is slower than desired. An indicator, such as a visual signal indicator can be activated to attract the user&#39;s attention and thereby to help avoid or alleviate the formation of poorly treated or under-treated skin segments. This maintains the proper efficacy of skin treatment. It should be appreciated that the indicators as presented are just a non-limiting example and any of a variety of types of indicators including speakers, buzzers, vibrators, lights, etc can be used for any of the various alerting requirements. 
     The applicator may be configured to automatically change the RF energy coupled to the skin. In such mode of operation, where the applicator is displaced at an almost constant speed, a controller based on the rate of temperature change may automatically adjust the value or magnitude of RF energy coupled to the skin. For example, at a high rate of temperature change the magnitude of RF energy coupled to the skin will be adapted and reduced to match the applicator displacement speed. At lower rates of temperature change, the magnitude of RF energy coupled to the skin will be increased to match the applicator displacement speed. The user or operator may be concurrently alerted in a manner disclosed hereinabove. This mode of operation also maintains the proper efficacy of skin treatment. 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the method. Accordingly, other embodiments are within the scope of the following claims: