Carboxytherapy on the treatment of managing cellulite and striae distensae: A systematic review

The use of carboxytherapy has shown excellent results in the treatment of various aesthetic conditions. The aim of this study was to investigate the effects of carboxytherapy on cellulite and striae distensae (SD). Therefore, a systematic literature review was accomplished on two databases, Medline via PubMed and Scopus, from July to August 2021. Studies that evaluated the effect of carboxytherapy on SD and cellulite were included, eight articles of all of them and that treated 299 people were included in this systematic review and the most studies classified as having low level of methodological quality. There was no consensus regarding the parameters used, but in most studies and applications were performed at a depth of 10 mm with a flow ranging from 50 to 150 mL / min. The results this intervention produced an improvement in skin aspects, with better texture, decreased severity of cellulite and SD, improved patient satisfaction, increased skin thickness, decreased edema and increased inflammatory infiltrate the number of collagen fibers. Some side effects were observed, such as transient erythema and post-inflammatory hyperpigmentation, leading to discomfort. However, all these adverse effects are transient, and patients can return to normal activities with the use of photoprotection. This review demonstrates the stimulatory effect of carboxytherapy on the symptomatology of patients with cellulite and SD.


Introduction
Carbon dioxide (CO2) therapy or most commonly carboxytherapy has been used since 1932 and it refers to the administration of CO2 with therapeutic proposals (El-Domyati et al. 2021). The mechanism of action of carboxytherapy is not well understood yet. However, it is believed that injection of carbon dioxide induces changes in the microcirculation, including vasodilatation and consequently the enhancement of local blood supply, stimulation of neoangiogenesis and increase of local metabolism (Matsumoto et al. 2018). Once in contact with tissues, CO2 reacts with water molecules, and molecular carbonic acid is formed and, as consequence a decrease of pH is observed. As a consequence, a lower pH produces an increase of oxygen release from haemoglobin, a reduction of divalent calcium ions and the split of carbonic acid to H + a HCO 3-, resulting in calcium hydrogen carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate formation (Matsumoto et al. 2018;Patel et al. 2021).
Based on these molecular and physiological modifications, carboxytherapy has become one of the most effective therapeutical interventions for dermatological and aesthetic proposals (Kroumpouzos et al., 2021). There are plenty of evidences demonstrating the positive results of carboxytherapy on the treatment of arteriopathies and ulcers, hypertrophic and keloid scars, alopecia, post liposuction conditions, wrinkles and for decreasing body fat (Lokhande, & Mysore, 2019;Jamshidian-Tehrani et al., 2020). For example, El-Domyati et al (2020) (demonstrated that carboxytherapy was able of producing facial rejuvenation and improving some aspects of wrinkles. Also, Ferreira, Haddad e Tavares (2008) described the increase of of the index of collagen remodeling induced by intradermal injections of CO2.
In addition, carboxytherapy has been widely used to treat cellulite and striae distensae (SD) or stretch marks. Cellulite is caused by excessive stretching of the skin, with a dermal damage and it is characterized by a visible linear scar (Pianez et al. 2016). The appearance of cellulite is multifactorial and it is related to an altered dermal connective tissue framework, involving the components of extracellular matrix (ECM) especially fibrillin, elastin, fibronectin and collagen (Mitts et al., 2005). Its appearance is relate dto a genetic predisposition, mechanical stress, hormones especially corticosteroids (both topical and systemic) and lifestyle (Lokhande & Mysore, 2019). Moreover, SD is characterized by skin atrophy with elongated form, Research, Society andDevelopment, v. 12, n. 8, e3612842520, 2023 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v12i8.42520 3 sometimes wavy, elevated, flat or depressed, but always soft and depressive. The color of SD can be pale or bluish when recent, and pearly white towards the end. When touched, they seem soft with a relative emptiness as if the skin was over a mobile and fleeting plan (Lokhande & Mysore 2019;Podgórna et al., 2018).
Many treatments for cellulite and SD have been reported including creams and electrophysical agents such as higher power lasers and radiofrequency therapy (Lokhande & Mysore, 2019). In addition, the positive effects of carboxytherapy as an effective therapeutical approach for these affections have also been highlighted (Rawlings, 2006). The mechanisms of action of carboxytherapy on the treatment of cellulite and SD is based on the stimulation of blood circulation and increase of oxygen release from oxyhaemoglobin by the presence of CO2, activating the synthesis of collagenase, elastin and hyaluronic acid by stimulation of fibroblast function, which seems to improve the aspect of cellulite and SD (Rawlings, 2006).
Although all the positive results of carboxytherapy for the treatment of cellulite and SD, its use is still controversial.
However, to the best of the authors' knowledge, no systematic review has evaluated the effects of carboxytherapy on the aspects and symptomatology of related to cellulite and SD. In this context, the aim of this study is to systematically review the literature investigating the effects of carboxytherapy on cellulite and in SD.

Methodology
This systematic review was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) (Liberati, et al. 2009) orientations. Medline via PubMed and Scopus were searched, the following search strategy was developed at PubMed database and was modify according to each database requirement: (("carbon dioxide") OR ("carboxytherapy")) OR ("carbon dioxide therapy")) AND (("cellulite") OR ("striae distensae")).
The search was performed from June to August of 2021. Articles were selected based on the titles, abstracts and full papers meeting the eligibility criteria. This systematic review was registered on the online international prospective register of systematic reviews (PROSPERO) of the National Institute for Health Research (under the number CRD42021275984).
Furthermore, articles included in this review had their methodological quality assessed by the PEDro scale Physiotherapy Evidence Database.

Study type
Articles that used carboxytherapy as a main intervention to treat cellulite and SD were selected. It is important to emphasize that it was not possible to perform a meta-analysis due to the heterogeneity of the primary studies.

Inclusion criteria
The following inclusion criteria were considered: • Articles written in English.
• Only studies reporting the treatment of cellulite or SD with carboxytherapy were considered.
• Control group could be a group without any treatment or a group with the use of a different treatment modality.
• The outcomes of the articles included had to evaluate photographic register and any skin assessment and report of interventions.

Exclusion criteria
• Studies were excluded if they included only in vitro and in vivo studies.

Outcomes Assessment
Data were extracted from included studies by 2 reviewers using standardized forms. The study database included basic characteristics of qualified studies (first author, published date, country), characteristics of the subjects (age, gender), interventions, characteristics of the parameters of carboxytherapy application and the use of other therapeutical interventions.
The outcome measures comprised digital photography and self-reported assessment.

Study selection
Two reviewers (CCSM and ACMR) independently analyzed title, abstracts and full paper versions of the studies and selected the potential studies according to the inclusion and exclusion criteria. After each step (title, abstract, full paper analyses), reviewers joined in a consensus meeting to check the agreement of in including all the selected papers. Two reviewers (PGV and JRP) evaluated methodological quality of the papers with the PEDro. The PEDro scale assesses the methodological quality of the articles, using a ranging from 0 to10 (0 being the lowest and 10 the highest methodological quality).

Results
The flow diagram demonstrates the search strategy used in the present study ( Figure 1). Forty nine articles were retrieved from the database Scopus,32 from PubMed, 49 from Web of Science, 24 from Cochrane and 7 from Google Scholar (in a total of 161). Then, the duplicated records were excluded (n = 53). Twenty-eight full-text articles were assessed for eligibility and 16 studies were excluded. Additionally, 8 studies were excluded for other reasons and finally, 9 studies were included and analyzed in this systematic review (El-Domyat, 2021;Pianze, 2016;Podgóma, et al. 2018;Sultan, 2018;Elmorsy, et al. 2021, Ahmed, & Mostafa, 2019Eldsouky, & Ebrahim, 2018;Hodeib et al., 2018).
Considering the methods used to evaluate the effects of carboxytherapy, clinical examination was used for 4 works (El-Domyat, 2021;Elmorsy, 2021Eldsouky, & Ebrahim, 2018Farouk, et al. 2022). Clinical assessment was based on a fivepoint scale (none = 0%, mild = 1 -25%, moderate = 26 -50%, good = 51 -75% and very good = 76 -100%) and evaluation of size, stage (color), depression or elevation, and skin texture (Elmorsy, et al. 2021;Ahmed, 2020) evaluated the improvement in width and texture. Patients were evaluated for their degree of improvement (by measuring the width of the largest striae before and after treatment) as follows: mild, moderate and excellent improvements.
Also, digital photographs were used for 7 studies, using the following score: −1 = worse, 0 = no change, 1 = weak (1-24% improvement in striae), 2 = moderate (25-49% improvement in striae), 3 = good (50-74% improvement in striae) 4 = excellent (75-100% improvement in striae). Pianez, (2016) evaluated cellulite grades by digital photographs with a digital camera following the score: 0= no alteration; I= skin affected area is smooth while the subject is standing or lying, but the alterations to the skin surface can be seen by pinching the skin or with muscle contraction (visible changes with skin clamping or muscle contraction); II= the orange peel aspect of the skin or mattress appearance is evident when standing, and III= the alterations described in grade or stage II, are present together with raised areas and nodules (visible changes associated with nodules). Podgorna et al., (2018) used 3 photos in a standing position and 3 independent evaluators compared clinical changes. Farouk et al., (2022) compared photographs before and after treatment using the Global Aesthetic Improvement Scale (GAIS) -5 means very much improved (optimal cosmetic result), 4 means much improved (marked improvement in appearance from initial condition but not completely optimal for this patient, a touch-up would slightly improve the result), 3 means improved (obvious improvement in appearance from the initial condition but tough-up or retreatment is indicated), 2 means no changes (appearance essentially the same as the original condition) and 1 means worse (appearance is worse than the original condition).
Another method used by 2 authors was the perception of patients after the treatment (self-reported analysis) (Elmorsy, et al. 2021;Ahmed, 2019). In these studies, each participant was asked to rate the overall satisfaction with the treatment 1 month after the last session using the criteria: "unsatisfied," "slightly satisfied," "satisfied," or "very satisfied but only satisfied" or "very satisfied. In another study (Farouk, et al. 2022) the perception of patients after the treatment was evaluated by Likert Satisfaction Scale (1=very unsatisfied, 2=unsatisfied, 3=neither satisfied nor unsatisfied, 4=satisfied, 5=very satisfied).
Histological evaluation and histomorphometry were used by El-Domyati et. al (2021) Research, Society and Development, v. 12, n. 8, e3612842520, 2023 (CC BY 4. Table 2 shows the parameters of carboxytherapy treatment. Related to the way of application, all the authors injected CO2 intradermally and most of them in the angle of 45 o . The depth of application ranged from 2 mm2 8 to 13 mm (Lee, 2010). CO2 flow varied from 50 ml/min to 300 ml/min (Elmorsy, et al. 2021;Eldsouky, & Ebrahim, 2018;). Number of sections were from 3 to 8 (Podgórna, et al. 2018;Pianze, 2016), in a treatment duration of 3 weeks to 6 months (Farouk, et al. 2022;Podgórna, et al. 2018). Some authors compared the effect of carboxytherapy with other treatments such as CO2 Laser, mesotherapy, tripolar radiofrequency device. Furthermore, carboxytherapy was more commonly applied at the regions of SD and cellulite. In table 3, it is possible to observe the results of all analysis and the outcomes presented in the papers in this systematic review. All the studies demonstrated that carboxytherapy was effective in attenuating the signals of cellulite and SD 8. In 4 studies, digital photographs showed that carboxytherapy presents improvement in skin texture8, decrease in the grade of cellulite morphological improvement with respect to the subcutaneous tissue, fibrotic septa and aspects of the dermis-related cellulite.
Also, ultrasound analysis demonstrated an improvement of the subepidermal thickness (Lee, 2010). Self-reported results showed that 60% of the patients showed excellent improvement, 20% showed good improvement and 20% showed moderate improvement (Elmorsy,2021). Also, it was demonstrated that 93.3% of patients treated with carboxytherapy was satisfied with the treatment (Ahmed & Mostafa, 2019). Thus, a study demonstrated that 20 patients (66.7%) were satisfied, 4 patients (13.3%) were neither satisfied nor unsatisfied, 3 patients (10%) were very satisfied and 3 patients (10%) were unsatisfied with carboxytherapy (Farouk, 2022). Four studies used histological and histomorphometry analysis and observed that the mean width and the mean length were significantly lowered after the treatment. Furthermore, morphological and architectural improvement of the epidermis, increase in the mean epidermal thickness and formation of collagen and elastin in the dermis (Eldomyat, 2021).
Furthermore, a decrease in oedema and inflammatory infiltrate and an increase in the number of collagen fibbers in the treated groups with carboxytherapy was also observed (Ahmed & Mostafa, 2019). Also, circumference measurement determined reduced values of thighs and statistically significant improvement in skin elasticity in 15 women with SD triae distensae (Ahmed, 2019). In all patients, the analysis of the results demonstrated a significant difference between the pretreatment and post-treatment values (Ahmed, 2019). Research, Society and Development, v. 12, n. 8, e3612842520, 2023 (CC BY 4. (2018) The response of treatment (grading scale) was mild in 4 patients (20%), moderate in 10 patients (50%), marked * Improvement and fibronectin-stained area after treatment * Carboxytherapy is an effective, safe, and novel method for the treatment of striae (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v12i8.42520 10 in 5 patients (25%), and excellent in only 1 patient (5%).
Pianez et al (2016) Statistically significant reduction in the aspect of cellulite; morphological improvement with respect to the subcutaneous tissue, fibrotic septa, and aspects of the dermis-related cellulite. * * * Improve of the severity of cellulite at the buttocks and posterior thighs of healthy women.
Lee (2010) Ultrasound evidence of decreased subepidermal thickness * * Significant reduction in upper, mid, and lower abdomen circumference occurred Confirming that carboxytherapy is safe and effective Source: Authors.

Discussion
This systematic review investigated the literature about the effects of carboxytherapy on the treatment of cellulite and SD. The results showed that this therapeutical intervention produced an improvement of the aspects of the skin, decrease of the grade measuring the severity of the cellulite and SD, improvement of the satisfaction of the treated patients, increase in the thickness of the epidermis, decreased edema and inflammatory infiltrate and increase in the number of collagen fibers. Also, reduced values of the circumference of different parts of the body were observed such as thighs. Moreover, the authors evaluated female volunteers, aging from 13 to 50 years, with different number of sessions and using different parameters.
Authors used different ways to evaluate the effects of carboxytherapy, but mainly digital photos and scales to compare the data before and after treatment and patient self-reported perception.
Cellulite and SD are common complaints in the area of aesthetic medicine and dermatology and it is related to multiple factors (Oakley & Patel, 2021). In this context, carboxytherapy has been highlighted as one of the most effective noninvasive therapy for these affections, aiming of stimulating blood flow, improving the skin's elasticity and reducing the appearance of cellulite and SD .
The site of application of carboxytherapy in the papers is concentrated in the area of occurrence of both skin affection (El-Domyat, 2021;Pianze, 2016;Podgórna, et al. 2018;Elmorsy, et al. 2021;Ahmed & Mostafa, 2019;Hodeib, et al. 2018;Lee, 2010). Also, many different ways of evaluation were used such as clinical evaluation, digital photos and scales. Cellulite and SD rating scales and photographs have been used for many authors in the literature, providing qualitative and quantitative data measurements (Young & Dibernardo, 2018). In spite of some limitations, scales are important tools for evaluating some clinical and histopathological aspects of cellulite and SD, including qualitative measure of severity (Rossi & Vergnanini, 2000;Emanuele, 2013). Although the importance of the use of scales in this field, many of them do not have a patient-reported component, which is highly recommended (Luebberding et al., 2015). It is important to highlight that some of the works in this review used the perception of patients after the treatment or self-reported analysis as a way of evaluating the effects of carboxytherapy (Ahmed & Mostafa, 2019;Elmorsy, et al. 2021;Farouk, et al. 2022 -Domyati, et al. 2021, El-Din et al., 2021El-Din et al., 2021 and ultrasound, measuring dermis, fibrotic septa and adipose tissue used by some authors of this review are also important tools of evaluation, such as digital photos. However, Young and Dibernardo (2021) points out that there is still a need for developing more accurate techniques for assessing cellulite and SD severity.
Moreover, a wide range of carboxytherapy parameters were used by the different authors. It is evident that the use of proper parameters of carboxytherapy is essential to reach key structures to obtain the success of the treatment and inadequate parameters can cause tissue damage (Almeida, et al.2020) . However, for carboxytherapy, the ideal parameters of application in the clinical settings is not well established yet and many controversies still remain (Khiat & Leibaschoff, 2018;Eldsouky & Ebrahim, 2018). Regarding, the infusion speed of the CO2, authors administrated CO2 in a velocity of 50 ml/min to 300 ml/min (Khiat & Leibaschoff, 2021;Ahmed & Mostafa, 2021). For most of the treatments, superficial (intradermal) injections require smaller gas volumes, i.e., 0.5-3 ml per injection spot, at a velocity of 30-40 ml/min. Superficial subcutaneous injections require 1-5 ml and deeper subcutaneous 5-50 ml per injection spot. Angles of insertion vary from 15-30º for superficial layers, 45º for superficial subcutaneous tissue, and 90º for deeper tissue (Oliveira et al., 2020).
Regarding the period of treatment and the number of sessions, there is no consensus among the authors. Number of sessions varied from 3 to 8 (Podgórna, et al. 2018;El-Domyat, 2021;Pianze, 2016) with an interval of 1 to 4 weeks between the sessions. The number of applications is dependent on the indication as well as the treated locality and in general it is necessary to repeat the application once or twice a week (Hodeib et al., 2018).
As it can be seen in table 3, carboxytherapy produced positive effects in managing and attenuating the signals of cellulite and SD, with improvement in skin texture (El-Domyati, et al. 2021, El-Din et al., 2021Hosam El-Din et al., 2021), a decrease in the grade of cellulite (Pianze, 2016;Hodeib, et al. 2018) and improvement of the general aspect of cellulite and SD (Pianez,2016;Podgórna, et al. 2018;Elmorsy, et al. 2021;Ahmed & Mostafa, 2019;Elmorsy,2021Eldsouky, & Ebrahim, 2018Hodeib, et al. 2018;Farouk, et al. 2022;Lee, 2010;El-Domati, 2020). Also, histological analysis demonstrated that carboxytherapy improved the subcutaneous tissue, fibrotic septa and aspects of the dermis-related cellulite (Pianez, 2016) and the ultrasound demonstrated evidences of decreased subepidermal thickness (Lee, 2010). Other important findings are related to the self-reported results, demonstrating that most of the patients considered the improvement after carboxitherapy as "excellent".
Also, it was demonstrated that 93.3% of patients treated with carboxytherapy was satisfied with the treatment (Ahmed & Mostafa, 2019).
One of the main modifications produced by carboxytherapy is the improvement of microcirculation function, increasing blood flux and tissue oxygenation (Oliveira, 2020). Moreover, it activates fibroblasts and consequently, increase collagen and elastin formation and deposition (Maia-Figueiró, et al. 2012). For example, El-Domyati, et al (2021) demonstrated an increase in collagen remodeling after 4 month of treatment in patients with SD. All of these modifications could explain the positive effects of carboxytherapy on cellulite and SD. Moreover, some side effects were seen such as transient erythema and post inflammatory hyperpigmentation, leading to the discomfort. However, all these adverse effects are transients and patients could return to normal daily activity with the use of photoprotection.
Furthermore, it is important to highlight a limitation of the present study related to the methodological quality of the included studies. The works included in the present review were not double-blinded being the evaluators or clinician aware of the interventions and groups.

Conclusion
In conclusion, this review demonstrates the stimulatory effect of carboxytherapy on the symptomatology of patients with cellulite and SD. However, there is no consensus about the parameters used by the different authors, making it difficult to compare the results. Also, the methodological quality of the study could be considered low. Further studies are necessary, considering a higher scientific rigor, especially for the description of all parameters and a higher sample size, in order to clarify the effects of this promising therapeutical intervention in order to define better protocols for treating both skin affections.