The sphere of cosmetology has been experiencing major progress in recent decades and now offers an extensive selection of beauty treatments at low costs. The desire of people to change or enhance their physical appearance drives the industry forward, and hair and skin treatments constitute the two primary sources of demand. The use of light sources is common in the field of cosmetology, and the two most prominent technologies are intense pulsed light and laser devices. Although both of them utilize light as the key component, they are different and possess unique features and characteristics. The current paper will explore in detail the aspects of the implementation of intense pulsed light and laser devices such as Nd:YAG and alexandrite lasers. Specifically, information will be provided on how these technologies can be used for skin rejuvenation treatments and hair removal on the face and body.
As mentioned above, there are many differences between intense pulsed light and laser devices, and one of the main of them concerns the wavelengths used in these two types of therapies. Intense pulsed light (IPL) devices emit multiple wavelengths at the same time. The appropriate wavelengths of IPL devices, such as EpiLight in the case of hair removal procedures, range from 590 to 1200 nm (El-Domyati et al., 2017). At the same time, IPL devices can utilize special cut-off filters which can limit certain wavelengths. Specifically, cut-off filters are primarily used to remove shorter wavelengths in order to ensure that only the longer ones are emitted since they are more deeply penetrating. Such filters, namely the 755 nm one, are used in hair removal procedures performed on people with darker hair. IPL devices also can be used successfully in skin rejuvenation treatments with the wavelength spectrum set at 1200 nm (Abrouk et al., 2022). Thus, in both types of treatment, the shorter wavelengths are cut off to achieve the desired results in removing hair and rejuvenating skin.
The hair removal and skin rejuvenation treatments also can be performed with the help of laser devices such as Nd:YAG and alexandrite lasers. The former devices, which include Lyra and CoolGlide, always use 1064-nm wavelengths which are deeply penetrating and can reach the hair follicles (Dorgham and Dorgham, 2020). Such a wavelength has a reduced absorption by melanin which implies the need for higher treatment fluences in order to damage the hair structure properly. At the same time, the poor absorption by melanin at 1064-nm, as well as the epidermal cooling device used by Nd:YAG lasers, make them a safe tool for hair removal and rejuvenation treatments. Moreover, Nd:YAG lasers are frequently used on patients who have the darkest skin phototype.
Alexandrite lasers are another laser technology device extensively used for the removal of hair on the face and body, as well as for skin rejuvenation procedures. An alexandrite laser’s main distinctive feature is the use of an alexandrite crystal which constitutes the source of the laser or medium. The primary function of the alexandrite laser is the production of a certain wavelength of light in the infrared spectrum. Specifically, alexandrite lasers utilize a wavelength of 755 nm, which makes them red-light lasers (Nistico et al., 2018). The wavelength has been found to be effective in the removal of hair. Although alexandrite lasers are not used as a solution for skin rejuvenation treatments, there is evidence that they can help to reduce skin dryness (Pancar, Kalkan and Eyupoglu, 2020). Thus, alexandrite lasers are a common tool in cosmetology used primarily for hair removal.
A major principle which needs to be taken into account when utilizing the aforementioned treatment methods is selective absorption. The phenomenon of selective absorption refers to the idea that absorption of certain wavelengths of intense pulsed light and laser devices depends on skin types or, particularly, their chromophores (Evans et al., 2017). Specifically, chromophores constitute regions in molecules where the difference in energy between two molecular orbitals exists within the visible spectrum range. Any light which reaches chromophores is absorbed by exciting an electron. In the case of hair removal and rejuvenation procedures, the main organ is the skin which has three primary chromophores, hemoglobin, water, and melanin. Thus, selective absorption implies that maximal absorption of certain light sources occurs when their wavelengths approximate the wavelength of the chromophores.
IPL devices produce a range of different wavelengths and thus are rather flexible and can be used on different skin types. As a result, IPL devices, unlike lasers, can target several chromophores at the same time and thus be more effective to a certain extent. Melanin is a chromophore which tends to absorb light mostly in the lower wavelengths, as a result, the darker skin absorbs more light. Therefore, IPL devices, when targeting melanin for hair removal procedures, utilize wavelengths from 500 nm to 800 nm and 980 nm for darker skin (El-Domyati et al., 2017). In the case of skin rejuvenation treatments, IPL devices use longer wavelengths of more than 1200 nm to target water. Therefore, IPL uses several wavelengths depending on the skin type and chromophores which are being targeted.
Unlike IPL, Nd:YAG and alexandrite lasers cannot change their wavelengths and thus have specific use cases and can be utilized on particular chromophores and skin types. Nd:YAG is a laser that uses the longer wavelength of 1064-nm and targets several chromophores, yet primarily the hemoglobin (Dorgham and Dorgham, 2020). Due to the fact that Nd:YAG uses longer wavelengths, it is used for the removal of hair and skin rejuvenation, particularly on darker skin types which have a high level of melanin. Alexandrite lasers which have a wavelength of 755 nm, are primarily absorbed by melanin and used for hair reduction for lighter skin types.
The use of the aforementioned technologies is guided by numerous principles, and one of the basic ones concerns selective photothermolysis. The concept of selective photothermolysis postulates that thermally mediated radiation damage should target only the chosen pigmented targets, both epidermal and dermal, at the structural levels of cells or tissues (Martella and Raichi, 2017). As a result of the implementation of the selective photothermolysis principle, the tissues which surround the targeted structures, such as the overlying cells, do not become affected by the intervention. Thus, potentially nonspecific, widespread thermal injury can be reduced or completely avoided. As mentioned above, the main skin chromophores are water, hemoglobin, and melanin. All of these chromophores have relatively broad absorption peaks of light energy, which allows them to be successfully targeted by a range of wavelengths or specific light. The broad absorption peaks of chromophores make it impossible to engage in selective heating of the targeted structures only, even when using monochromatic light beams.
In the case of IPL devices which emit a broad range of wavelengths, different chromophores are targeted concurrently since they get affected by green, yellow, red, and infrared light. When engaging in the hair removal procedure, it is important to target melanin which is contained primarily in the hair follicle epithelium and not in other areas. Thus, IPL devices utilize longer wavelength settings up to 755nm when removing hair to perform selective photothermolysis. In terms of skin rejuvenation, the principle of selective photothermolysis implies using the 1200 nm setting since such a wavelength spectrum is absorbed by water in the dermis, stimulating new collagen formation (Bibilash et al., 2017). Therefore, different types of wavelengths need to be utilized according to the aforementioned principle.
The selective photothermolysis concept also applies to the utilization of Nd:YAG and alexandrite lasers. As already mentioned, the hair removal procedures mainly imply targeting melanin and Nd:YAG, which uses higher wavelengths and thus is more effective in darker skin types. Alexandrite lasers rely on the principle in question by targeting the melanin in lighter skin types since they use shorter wavelengths.
The need to adhere to the principle of selective photothermolysis is also important not because otherwise, an intervention will be ineffective but because non-compliance may lead to detrimental consequences. The incorrect choice of a wavelength spectrum of IPL in the instances of hair removal can cause hyperpigmentation due to the impact on melanin which results in darker skin spots. At the same time, hypopigmentation is also possible when using IPL for hair removal. There is also evidence that the improper use of IPL devices can lead to erosions and crusts on the skin (Bibilash et al., 2017). In the case of rejuvenation procedures, the symptoms are similar, yet, there also can be persistent erythema which is redness on the skin. Additionally, people undergoing rejuvenation interventions using IPL may gain hypertrophic scars.
Similarly, the incorrect use of Nd:YAG and alexandrite lasers and non-adherence to the selective photothermolysis principle can have negative implications. The complications which arise are, to a significant extent, the same as in the case of IPL. Specifically, patients may have hypopigmentation and hyperpigmentation on their skin, as well as blistering and crusting. There is also a possibility of edema being developed which constitutes a spot retaining excessive fluid. The condition which is particularly notable in the case of hair removal procedures using lasers is folliculitis which is an inflammation of hair follicles. Thus, it is important to use the devices in question in an appropriate way while observing the principle of selective photothermolysis.
The utilization of intense pulsed light and laser devices such as Nd:YAG and alexandrite lasers in treatments such as hair removal and skin rejuvenation have been found successful. At the same time, it is important to note that each device should be used in accordance with the principle of selective photothermolysis. As a result, it is essential to analyze each case and to choose the right wavelength spectrums. For instance, intense pulsed light is a flexible solution which can change wavelengths and thus can be adjusted for different situations. For example, IPL devices must have a 755 nm setting when removing hair and a 1200 nm setting when performing skin rejuvenation procedures. Nd:YAG and alexandrite lasers have fixed wavelengths which have been thoroughly studied and recognized as effective in removing hair. Nevertheless, the higher wavelengths of Nd:YAG are more appropriate for darker skin types, while alexandrite lasers are the choice for lighter skin. Setting the correct wavelength setting when removing hair or performing skin rejuvenation is a must because, otherwise, interventions may damage the health of the patient.
Reference List
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