A unique method to protect the epidermal layer from thermal injury.

Introduction
Removal of unwanted body hair is of major importance to most women and to increasing numbers of men who spend tremendous sums of money and invest much time and energy in pursuit of this smooth look. Over 80 million women use depilatories, epilators, waxing or shaving kits on a regular basis spending an estimated $500-$600 million annually. Over $1 billion is spent annually on electrolysis, which is a painful and invasive procedure requiring many treatments. An exciting new development is the use of intense light devices for hair removal. The potential benefit of photo-epilation over existing methods is faster treatment. Photo-epilation also has some risks associated with it due to the application of high energy light to the skin. For this reason it is important that this mode of hair removal be conducted by properly trained medical practitioners, who understand the clinical applications as well as the dynamics of light-tissue interaction. Removing unwanted hypertrychotic and hirsutic hair using intense light requires that the hair shaks and follicular structures be heated to a high enough temperature to induce thermal injury. The chromophores responsible for light absorption in the hair follicles are melanin (eumelanin and pheomelanin), which are part of the cellular components of these structures. However, melanocytes containing eumelanin are also found in the epidermis and in the epidermal/dermal junctions. The concentration of the eumelanin varies according to skin type. Intense light applied to skin with high concentrations of melanin may cause unwanted adverse effects since the eumelanin in the epidermis competes with the melanin in the hair shaft and follicles for the absorption of the intense light. Commercially available light devices use lasers and high fluence pulses to attempt to combat this problem. However, unlike laser systems, EpiLight Hair Removal System uses a pulse mode technique, inherently related to its non-laser principle of operation, which divides the desired fluence into multiple pulses and amplifies the effect of hair destruction, while sparing the skin.
EpiLight Hair Removal System is designed with maximum flexibility to ensure safe and effective hair removal with little to no risk of unwanted thermal damage to the dermis and epidermis.

Differential heating of epidermis and follicle by light pulses
Tissue which is heated to temperatures higher than surrounding tissue cools by conduction of the excess thermal energy to its surroundings. The time interval during which the temperature is equalized to its surroundings is the thermal relaxation time. The relaxation time is strongly dependent upon the size of the heated object. It is given by the relation:-  tr=d2/ga - where tr is the thermal relaxation time of the object, d2 is the dimension of the target, g is a geometrical factor, and a is the thermal tissue diffusivity. Figure I presents the cooling times of the epidermis and of hair follicles of different sizes. According to Figure I the cooling time of the epidermis is between 8-10 ms, while the cooling time of hair follicles (0.2-0.3 mm. in diameter) is 20-60 ms. The difference between the cooling times suggests how in principle, the follicles and the epidermis could be differentially heated by pulsed light. Idealiy, if the duration of the light pulse is between the cooling time of the epidermis and the relaxation time of the hair follicles, say 15-40 ms, it should be possible to cool the external skin and in this manner to extract heat from the epidermis by conduction, whereas the heat injected into the follicles is bound to remain confined in their anatomy. Indeed, in this case, the hair follicle could be destroyed, sparing the epidermis. EpiLight Hair Removal System's pulse sequencing technique puts this theoretical concept into practice. Using this reasoning, it is possible to significantly spread the high light fluence required for hair follicle destruction over a number of successive pulses. For example a time delay of 20ms is introduced between the individual 3ms long pulse segments, which is significantly longer than the relaxation time of the epidermis, but shorter than the cooling time of the hair follicle. The temperature of the epidermis decays during the long delay intervals as a result of the thermal contact of the outer skin with the cooling gel. Conversely, the heat injected into the hair follicles can not diffuse into the surrounding tissue because pulses are fired at intervals shorter than their relaxation time. The heat accumulates from pulse to pulse in the follicles, until tissue denaturation occurs. Figure 2 demonstrates the temperature distribution in and around a hair follicle, as a function of depth and lateral spread. The temperature values were calculated using Monte Carlo simulations which follow individual photon tracks and average the fluence and energy deposition distribution for a large number of photons (1,000,000). Denaturation temperatures are achieved all along the hair follicle, down to its full depth. At the same time, the temperature of the epidermis is not raised excessively. Cooling time of the hair and the hair follicle are a function of hair thickness. Cooling time varies by a factor of 16 between a 0.05mm external hair diameter and a 0.2mm follicle diameter. The delay between pulses is varied, according to skin color, hair color, and the depth of the follicle. For example, the darker the color of the skin the longer the delay between pulses which enable the epidermis to conduct away a larger heat quantity absorbed by the dark skin.

EpiLight – Today's Answer for Effective Hair Removal
Clinical results indicate that EpiLight Hair Removal System safely and successfully eliminates hair of all colors, black, brown, red, blond and even white, enabling physicians to widen their base of potential patients. The before and after pictures shown here demonstrate its high degree of selectivity. Hair was removed from the trunk, pubis, and breasts of a young patient. In spite of the high degree of pigmentation in the nipples, and the sensitivity of this area, hair can be removed effectively and selectively while maintaining the excellent appearance of the normal surrounding tissue. EpiLight 's high degree of success is a result of the flexibility to tailor treatments and adjust parameters to fit the patient's needs. Pulse sequences can be varied from two to several, with pulse durations and the delays between them adjusted according to patient skin type, hair color and location. The multiple pulsing capability, a unique feature of EpiLight, maximizes selectivity of treatment and minimizes side effects in the surrounding skin. The large spot size enables large areas to be covered quickly, reducing treatment time. Wavelength range selection provides flexiblity in treating hair of different colors and in varying depths of skin. These versatile features are unique to EpiLight and are unmatched by any other existing hair removal system.

26 year-old female with black hair on chin. Before and after four treatments with a break of 3, 4 and 5 weeks respectively.

Foto gentilmente concesse da David Wilder, MD, Oberndorf, Germany.

21 year-old female with dark hair on truncal area. Before and after four treatments.

Foto gentilmente concesse da Christian Raulin, MD, Karsruhe, Germany.