1. IntroductionStriae distensae (SD), also known as stretch marks, affect a large part of the world’s population and are becoming challenging to treat. In 1936, the first correct description of these lesions appeared, entitled as striae atrophicae [1]. Stretch marks are linear prevalent cutaneous lesions [2], characterized by epidermal atrophy [3]. The exact origin of this type of skin condition remains unclear; however, they occur mostly in some physiological and pathological situations, such as in adolescent growth, obesity, pregnancy, and topical steroid use [3,4]. Stretch marks appear at a higher frequency in pregnant woman and adolescents, in whom the prevalence ranges from 6 to 86% [5]. Lower back and knees are the most affected areas in males, while in women they mostly affect the calves, buttocks, and thighs [5].Clinically, stretch marks are characterized by rapid elongation of the skin, which destroys the elastic fibers, affecting the dermis by decreasing the components of the extracellular matrix (ECM) such as collagen and elastin [5]. In the early stages, SD appear in a pink-red-purple color, with edematous scars called striae rubrae [5,6]. Over time, a decrease in vascularization is observed, with a degradation of collagen and elastin [5], which turns the striae into a white color with an atrophic look, known as striae albae [4,6]. Other different stria types have been identified such as striae caerulea and striae nigrae in individuals with darker skin, which are associated with an increase in their quantity of melanin [7]. Studies also demonstrate that different colors in stretch marks are influenced by melanocytes’ mechanobiology [8].Despite being a physiological condition, striae still represent a disfiguring condition that creates a lot of psychological problems, affecting the quality of life of any individual with this pathology [9]. Many people look for therapies and treatments, and several have been proposed such as chemical peels, microdermabrasion, topical agents, and ablative and non-ablative energy devices [5]. However, the treatment of SD does not bring 100% effective outcomes since there is no consistent modality available [4]. In the late stages of striae, it becomes even more challenging to find a more effective treatment [2]. One of the modalities that is lately being used to upgrade and recover stretch marks is laser therapy [4], which represents an innovation in the approach to striae, particularly in striae rubrae [10], and is the most common therapeutic alternative recently [11]. Lasers should recover both striae depth and width as well as improve their histology, with an increase in the numbers of collagen and elastin fibers [12].Skin lasers have improved, even more so after the development of fractional laser treatment, which is characterized by reepithelization due to the migration of viable cells from undamaged sites to the injury site [9]. Laser categories include non-ablative fractional laser, radiofrequency (RF), long pulsed Nd:YAG, fractional CO2 laser, fractional bipolar RF, fractional ablative microplasma RF, and intense pulsed light (IPL) [13,14]. Laser therapy represents a great advance in treating stretch marks, specifically striae rubrae, since there is an increase in the vascularization of the lesions [10].Specifically, fractional CO2 laser treatment has been reported as a new resurfacing technique in SD treatments [9]. Here, fractional CO2 forms micro-thermal zones of damage, the necrotic debris is expelled, and neo-collagenesis occurs [15]. This technique stimulates epidermal turnover and dermal collagen remodeling, which leads to important improvements in texture and appearance in many types of scars, such as stretch marks [16]—mainly in mature striae [2]. After treatment with fractional CO2 laser, full recovery with normal epidermis, parallel arrangement of the collagen bands, and perivascular aggregation of inflammatory cells were demonstrated [16]. In phototype IV skin, the use of CO2 laser treatment has been discouraged on account of the high risk of pigmentary alteration [17], although theoretically, this type of laser stimulates fibroblast activity and improves lesions through controlled skin abrasion [18]. Regarding adverse effects, there are a few, and some are self-limiting, such as post-inflammatory hyperpigmentation; however, these effects can be fixed naturally in a few months after treatment [2].Additionally, CO2 laser treatment is more painful and requires a longer recovery time [19] when compared with non-ablative lasers. Studies have shown a significant decrease in the strial surface area after resurfacing with fractional CO2 laser treatment when compared with topical therapy (10% glycolic acid + 0.05% tretinoin) [20]. Lee et al. also demonstrated that fractional CO2 laser treatment, specifically at 10,600 nm, had a positive effect on late-stage SD, with clinical improvement with only one session [21]. When used in striae albae, fractional CO2 laser treatment was shown to be effective in subjects with skin types III and IV [20], and another study also demonstrated that two out of five patients with striae albae showed changes after 4-week treatment intervals with fractional CO2 laser [22].Concerning RF, this type of technique provides different patterns of heat distribution [23]. Unlike lasers, which convert light to heat and focus on specific chromophores, RF devices transfer a high-frequency alternating electrical current that goes through the dermis and hypodermal tissues without affecting the epidermal–dermal barrier [2]. That electrical current is converted into heat, mediating thermal damage to the surrounding connective tissue responsible for denaturing elastic fibers and collagen [24], which occurs immediately after RF treatment [4]. This collagen denaturation represents the tissue contraction, which induces inflammation and stimulates fibroblasts to produce new collagen, new elastin, and ground substances [3]. These alterations intensify the dermal tissue and help to improve the appearance of striae due to the increased production of collagen and elastin [3,24]. Regarding bipolar RF, it has shown clinical and histological improvements in striae distensae, while tripolar RF resulted in a 25–75% improvement in just one week of treatment [25]. Overall, RF is associated with an increase in the production of the dermis, improving SD [26]. A study showed that 14 of 16 subjects observed visible changes, with statistically significant reductions in both the length and width of striae bands [3]. To improve the tissue heating patters, fractional radiofrequency (FRF) was developed, which induces dermal heating [23]. FRF is safe for all skin types due to its “colorblind” nature, being applied directly to the skin surface or within the skin [23]. Even though the side effects were mild and transient, pain remains a significant limitation to the use of FRF, specifically in sensitive body areas such as the abdomen [27].

Overall, only a limited number of studies have been conducted that investigated the effectiveness of different types of treatments for stretch marks, specifically comparing two different types of treatment. Taking that into account and considering the characteristics of both fractional CO2 laser and fractional radiofrequency, we would like to focus this work on the evaluation and comparison of the clinical efficacy and treatment safety of both techniques in clinical applications (STRIAL). To evaluate the impact of stretch marks reduction on the quality of life and on body image, two hypotheses are proposed: the clinical efficacy and safety of fractional CO2 laser are superior to fractional radiofrequency, or the clinical efficacy and safety of fractional radiofrequency are superior to the fractional CO2 laser.

4. Discussion

As we mentioned before, from a previous review of the literature, we concluded that for an accurate assessment of efficient treatments for striae, more clinical studies with a significant sample are necessary. Therefore, our trial seems to be an innovative study exploring the influence of stria treatment on the health-related quality of life of patients undergoing fractional CO2 laser or fractional radiofrequency treatment. To overcome some limitations found in the literature, we propose a randomized controlled trial with a sample of 60 individuals. This sample would be important to increase the probability of including both men and women and participants with different types of skin and strial bands.

With the proposed trial, we expect to validate the fractional CO2 laser and fractional radiofrequency protocols in terms of efficacy and safety, which can be useful in the management of physical characteristics linked to striae. With this study design, we expect to find evidence that the treatments could demonstrate significant differences, such as a reduction in the length and width of striae bands. With respect to the primary outcomes, we will explore the quartile scoring criteria prepared for the assessment of clinical improvements in the affected area (abdomen) before and after the respective treatments, and we expect to see differences by comparing the digital photos taken in these timelines, using Figure 4 as the control. Regarding the secondary outcomes, we will explore the measurements of cutaneous temperature, skin pH, and skin elasticity to assess any inflammatory processes and to describe differences in different skin aspects after each treatment.

In addition, we will try to assess the impact of stretch mark reduction on body image, through a scale that evaluates the quality of life, the BODY-QTM Scale—Appraisal of Stretchmarks.