Introduction
Silicone-based products are widely used for the treatment of hypertrophic scars (HS) [1-4]. Even if the mechanism of silicone-based products has not yet been fully revealed, they are known to be effective in flattening and softening HS, as well as reducing symptoms such as redness, stiffness, pain, and pruritus [4-11]. Topical silicone gel (TSG) and silicone gel sheet (SGS) are the most representative forms among various silicone products.
Silicone-based products are more effective when used continuously and consistently. It is usually recommended to use TSG twice a day, and SGS 12–24 hours a day, for 3–6 months [1,2]. However, such continuous and consistent application of silicone-based products on scars can be challenging to implement. For cosmetic reasons, some patients refuse to keep applying SGS on exposed areas such as the face. SGS can fall off easily or restrict movement on joint areas. SGS can also cause skin irritation or dermatitis if applied continuously, which can also make consistent application difficult [1,2]. In these cases, TSG, which forms a thin and transparent silicone layer on the applied area, can be used instead. TSG is easy to apply, is less noticeable, and causes fewer skin problems than SGS. However, it is still not easy to apply TSG regularly and constantly every day for extended periods of time.
We became interested in whether continuous and consistent use of TSG and SGS could improve scar outcome, whether there was a correlation between compliance and scar outcome, and which scar characteristics would improve. We hypothesized that better compliance of TSG and SGS would improve overall HS characteristics. This randomized controlled clinical trial was conducted to evaluate patients’ compliance and scar outcomes after the application of TSG and SGS on HS.
Methods
This study included male and female patients aged ≥18 years who visited this outpatient clinic for HS treatment between January 2020 and January 2023. The development of HS in our patients were due to prior surgery or trauma. The following exclusion criteria were applied: age less than 18 years; additional scar treatment during follow-up period such as laser therapy or steroid injections; presence of an open wound surrounding the scars; severe skin troubles caused by silicone products; and cases where the patient discontinued treatment or visited the outpatient clinic without consent. Patient consent to the study was obtained, and this study was approved by the Institutional Review Board (IRB File No. 2023-11-012-002) of Kyung Hee University Hospital.
Patients who met the inclusion criteria were invited to participate, and to those who agreed, one of two products (TSG or SGS) was randomly prescribed. A physician who had not seen the patient randomly selected a card that had the type of silicone product written on it, and the corresponding patient was prescribed the randomly selected product. Kelo-Cote (Alliance Pharma) was used for TSG, and NewGel+ (Newmedical Technology) was used for SGS.
One physician and two nurses provided verbal instructions on how to use the silicone products, utilizing a 1-page handout [1,2]. Patients prescribed TSG were instructed to apply it twice a day (morning and evening) to their HS, gently spreading the gel until a thin layer is formed. Patients prescribed SGS were instructed to apply to their HS for at least 12 hours a day, gradually increasing to 24 hours a day. Patients in the SGS group were instructed to reuse the SGS by washing it with tap water every day for up to 1 week, then discard it and start using a new one.
When pruritis, skin rash, or urticaria occurred, patients were told to discontinue the use of the silicone products immediately and visit the outpatient clinic as soon as possible. Patients were told to use the silicone products consistently for 6 months, and to return to the outpatient clinic to get new products if they ran out of them. Patients visited the outpatient clinic every 3–4 weeks for regular follow-up till 6 months. At each visit, patients were asked about their silicone product application frequency, including how many times they applied it in a day (TSG), how long they applied it in a day (SGS), and how many days per week they used their product.
Points system for patients depending on compliance
Patients were categorized into three subgroups based on the frequency and days of applying TSG and SGS, respectively. For patients using TSG, 1 point was assigned to those who applied TSG once a day for ≤3 days in a week. Two points were assigned to those who applied TSG twice a day for ≤3 days in a week. Three points were assigned to those who applied TSG once a day for 4–6 days in a week. Four points were assigned to those who applied TSG twice a day for 4–6 days in a week. Five points were assigned for those with TSG once a day for 7 days a week. Six points were assigned for those with TSG twice a day for 7 days in a week. The TSG subgroup 1 included patients with 1 to 2 points, TSG subgroup 2 included those with 3 to 4 points, and TSG subgroup 3 included those with 5 to 6 points (Table 1).
In patients who were assigned SGS, 1 point was assigned to those who applied SGS for ≤12 hours a day for ≤3 days in a week, 2 points were assigned to those who applied SGS for 12–24 hours for ≤3 days in a week, and 3 points to those who applied SGS for 24 hours daily for ≤3 days in a week. Four points were assigned to patients who applied SGS for ≤12 hours a day for 4–6 days in a week, 5 points were given to those who applied SGS for 12–24 hours for 4–6 days in a week, and 6 points were assigned to those who applied SGS for 24 hours daily for 4–6 days in a week. Seven points were assigned to those patients who applied SGS for ≤12 hours a day for 7 days in a week, 8 points were assigned to those who applied SGS for 12–24 hours for 7 days in a week, and 9 points were assigned to those who applied SGS for 24 hours daily for 7 days in a week. Patients with 1 to 3 points were included in SGS subgroup 1. Patients with 4 to 6 points were included in SGS subgroup 2, and patients with 7 to 9 points were included in SGS subgroup 3 (Table 1).
HS assessment
To assess HS, both physicians and patients evaluated the scar. We hereby defined HS as scars characterized by excess scar tissues confined within the boundaries of the initial wound [5]. If the skin at the scar appeared stretched or pulled apart, we referred to it as a widespread HS. The Vancouver Scar Scale (VSS) was used as an objective standard rating scale [12,13]. Two blinded physicians examined each patient and evaluated the scar based on the VSS (pliability, pigmentation, vascularity, and scar height) [12]. For patient self-assessment, a 10-point visual analogue scale (VAS; 0=no symptom, 1–3=mild, 4–6=moderate, 7–10=severe symptom) was used to assess scar height, pain, itching, pigmentation, and hardness. Each evaluator (physicians and patients) was unaware of previous scores or the scores given at each assessment. Additionally, digital images were taken of each HS by a digital camera at every assessment, maintaining the same distance and under predetermined lighting to allow for before-and-after comparisons.
Data analysis
Frequencies were calculated for categorical and binary variables, and mean and standard deviation were calculated for continuous variables. Continuous variables were analyzed using an independent t-test when data were normally distributed. Categorical variables were analyzed using the chi-square or Fisher exact tests when appropriate. Statistical significance was set at P<0.05. Statistical analysis was performed using SPSS version 22 statistical software (IBM Corp.). The t-tests and one-way analysis of variance (ANOVA) tests were used for statistical analysis.
Results
A total of 115 patients who met the inclusion criteria initially participated in this study. Among them, 36 patients who received combined scar treatments (laser therapy or triamcinolone acetonide injections), or who discontinued treatment before 6 months were excluded. Consequently, 79 patients finished this study, of which 38 received TSG, and 41 received SGS.
Demographics
TSG group
In the TSG group (n=38 [24 males and 14 females], mean age of 42 years), 30 had linear HS, while eight had widespread HS. Among these, nine patients earned 1 point, one patient earned 2 points, four patients earned 3 points, eight patients earned 4 points, one patient earned 5 points, and fifteen patients earned 6 points. Based on this distribution, TSG subgroups 1 (n=10), 2 (n=12), and 3 (n=16) were divided. There were no significant differences in sex, age, and HS types between the subgroups of the TSG group (Table 2).
SCS group
In the SGS group (n=41 [31 males and 10 females], mean age of 40 years), 28 had linear HS, while 13 had widespread HS. Among them, fourteen patients earned 1 point, one patient earned 2 points, no patient earned 3 points, five patients earned 4 points, six patients earned 5 points, no patient earned 6 points, two patients earned 7 points, five patients earned 8 points, and eight patients earned 9 points. Based on this distribution, SGS subgroups 1 (n=15), 2 (n=11), and 3 (n=15) were divided. There were no significant differences in sex, age, and HS types between the subgroups of the SGS group (Table 3).
Vancouver Scar Scale
TSG group
Regarding pigmentation, for subgroup 1, mean scores at baseline, 3 months, and 6 months were 2.09, 2.26, 2.13 respectively; for subgroup 2, 1.67, 1.40, 0.58; for subgroup 3, 1.60, 0.77, 0.13. Regarding pliability, for subgroup 1, mean scores were 1.96, 1.74, 1.39 respectively; for subgroup 2, 2.08, 1.21, 0.54; for subgroup 3, 2.13, 1.03, 0.20. Regarding vascularity, for subgroup 1, mean scores were 1.91, 1.70, 1.09 respectively; for subgroup 2, 1.58, 0.96, 0.63; for subgroup 3, 1.93, 1.17, 0.57. Regarding height, for subgroup 1, mean scores were 0.39, 0.57, 0.70; for subgroup 2, 0.29, 0.17, 0.08; for subgroup 3, 0.53, 0.27, 0.10. For each scar characteristic, repeated measure ANOVA and Bonferroni post hoc analysis were performed (Figs. 1, 2).
SGS group
Regarding pigmentation, for subgroup 1, mean scores at baseline, 3 months, and 6 months were 2.04, 2.18, 1.89 respectively; for subgroup 2, 1.57, 1.19, 0.57; for subgroup 3, 1.64, 0.82, 0.07. Regarding pliability, for subgroup 1, mean scores were 1.96, 1.71, 1.36 respectively; for subgroup 2, 2.10, 1.10, 0.33; for subgroup 3, 2.14, 1.04, 0.21. Regarding vascularity, for subgroup 1, mean scores were 1.84, 1.57, 1.07 respectively; for subgroup 2, 1.71, 1.00, 0.52; for subgroup 3, 1.96, 1.14, 0.57. Regarding height, for subgroup 1, mean scores were 0.36, 0.46, 0.57; for subgroup 2, 0.29, 0.19, 0.10; for subgroup 3, 0.57, 0.27, 0.11. For each scar characteristic, repeated measure ANOVA and Bonferroni post hoc analysis were performed (Figs. 3, 4).
Visual analogue scale
TSG group
Patient self-assessment for HS (height, pain, itching, pigmentation, and pliability) conducted at baseline and 6 months were compared. The results are summarized in Table 4. For height, pigmentation, and pliability, the difference between baseline and 6 months were statistically significant (P=0.004, P=0.019, and P=0.013, respectively). For pain and itching, the difference between baseline and 6 months showed no statistically significant values (P=0.226, P=0.538, respectively).
SGS group
The results for patient self-assessment for HS by VAS for the SGS group are summarized in Table 5. For height, pigmentation, and pliability, the difference between baseline and 6 months were statistically significant (P=0.032, P=0.019, and P=0.038, respectively). For pain and itching, the difference between baseline and 6 months showed no statistically significant values (P=0.413, P=0.178, respectively).
Discussion
In this study, longer and more frequent application of TSG and SGS resulted in better scar outcomes. When compliance was higher, patient self-assessment of HS also reflected better outcomes, except in pain and itching.
Current standard recommendations for silicone-based products are to either apply TSG to HS twice a day or use SGS for more than 12 hours a day, for a duration of 3–6 months [2,5,7,14]. However, these recommendations lack a precise theoretical foundation. It is controversial whether HS improves as the application duration of the silicone products increases. In the study of So et al. [15] including patients with burn scars treated with SGS, patients who applied SGS for a mean daily time of 22 hours demonstrated significantly better scar improvement compared to those applying it for 10 hours. On the contrary, Ahn et al. [16] reported that patients with a mean daily SGS application time of 12 hours or more did not demonstrate better scar improvement compared to patients with a mean daily application time of less than 12 hours. In another study including 25 patients with HS, two-thirds of the patients showed an improvement in scars although the SGS application time was 15 hours or less [17].
In order to reflect the total application time of silicone-based products more accurately, we calculated not only hours per day but also days per week. In this study, data showed that daily application hours were not proportional to weekly application days. In the TSG group, among those who applied TSG once a day, nine applied gel for ≤3 days weekly, four applied gel for 4–6 days, and one applied gel for 7 days. In those who applied gel twice daily, one, eight, and fifteen patients applied gel for ≤3 days, 4–6 days, and 7 days weekly, respectively. Among the patients who applied SGS on the scar for ≤12 hours daily, fourteen, five, and two patients used the sheets for ≤3 days, 4–6 days, and 7 days weekly, respectively. Among the patients who applied SGS on the scar for 12–24 hours daily, one, six, and five patients used the sheets for ≤3 days, 4–6 days, and 7 days weekly, respectively. Among those who applied the sheets on the scar for 24 hours every day, 0, 0, and 8 patients used the sheets for ≤3 days, 4–6, and 7 days weekly, respectively. Additionally, the patients were categorized into subgroups based on the application days, as we considered consistent and continuous use of silicone products to be crucial, in addition to application time. For example, we believed that a person who applied SGS for ≤12 hours per day for 7 days per week would actually apply SGS for a longer period of time compared to a person who applied SGS for ≥12 hours for ≤3 days per week.
Considering the results of this study, silicone-based products should be used continuously for at least 4 days per week to expect good results. The VSS results demonstrate that application of silicone products for less than 3 days per week aggravated pigmentation and scar height, especially in the TSG group. We speculate the reasons as follows. All scars tend to worsen over the first 3–4 months as collagen deposition and contracture take place while active anabolism increases [18]. Afterwards, anabolism slows down and collagenase tends to cause scar tissue breakdown. This allows HS to slowly begin to reduce in size, soften, and become less erythematous, through a process called scar maturation. Silicone-based products prevent HS development by promoting collagenase activity and reducing collagenesis. Although the mechanism of action of silicone products in HS has not yet been thoroughly revealed, it is known that once silicone gel dries up, it forms a thin and transparent silicone sheet, which increases the surface temperature of the skin and promotes collagenase activity breaking down collagen [3,19]. In addition, the occlusion and hydration effects of silicone sheets decrease the activity of fibroblasts [3]. Occlusion decreases water evaporation from the skin and thus causes hydration, and eventually leads to a reduction in collagen formation [20].
With infrequent application, such as less than 3 times a week, we presume that the skin temperature elevation, occlusion, and hydration effects of the silicone products did not work effectively. With the decrease of collagen breakdown, collagen deposition would have increased, as would had the scar height. We speculate that the reasons behind subpar scar improvement in the TSG groups compared to SGS groups are as follows. Silicone sheets are thick, and do not dry up or evaporate as a silicone gel would. This would allow the skin temperature to rise more easily, and naturally, the occlusion and hydration effect would be superior. Silicone sheets could thus keep the stratum corneum hydrated and also protect the skin from environmental hazards more so than gels, both effects leading to prevention of scar hypertrophy [3].
Regarding pigmentation, we used TSG containing sunscreen effects and opaque SGS which physically block sunlight to a certain degree. Therefore, it is assumed that when silicone products were less frequently used, exposure to sunlight was also increased, leading to increased pigmentation in scars.
According to the patient self-assessment VAS results, the patients reported improvements in scar height, pigmentation, and hardness as application time increased. This pattern was seen in both the TSG and SGS groups (P=0.004, P=0.019, P=0.013 for the TSG group; P=0.032, P=0.019, P=0.038 for the SGS group). Pain and itching improved regardless of the application time. We assumed that the innate hydrating and lubricating effects of silicone-based products improved pain and pruritus, even when not applied often. Regardless of compliance, the continuous use of the silicone-based products reduced pain and pruritus to a certain amount after 6 months. Since those who discontinued using the silicone-based products before 6 months were excluded from this study, all participants continuously used the products for 6 months, regardless of frequency. In short, consistent use of the silicone-based products reduced pain and pruritus despite of poor compliance, which was consistent with other studies. Li-Tsang et al. [21] compared the therapeutic effects of silicone gel dressings and pressure therapy on the management of posttraumatic HS and reported that silicone gel dressings demonstrated a better reduction in pain and pruritus. Eishi et al. [22] demonstrated marked improvements in pain and pruritis after using SGS for the management of HS and keloids.
Current guidelines on scar management recommend avoiding sunlight exposure and the use of sunscreen until scar maturation [2]. Human and animal studies demonstrated that ultraviolet radiation would aggravate pigmentation and the clinical appearance of scars [23,24]. In this regard, the 1-page handout that we routinely provided to the patients also contained information about avoiding sunlight exposure. For this reason, we used silicone products which had inherent sunblock effects. This might have affected our results that silicone-based products improved pigmentation of scars despite that a previous study reported that silicone-based products did not have significant impacts on pigmentation improvement [25].
This study has several limitations. First, we relied on the memories and words of the patients considering product use frequency and duration. A more accurate monitoring of compliance could have strengthened our results, and for further studies, having the patients record their product use every day would help. Next, since the proportion of linear HS and widespread HS was 8:2, the characteristics of linear HS were mainly reflected in this study. Mustoe et al. [14] have previously recommended as a first-line treatment SGS for linear HS, whereas for widespread HS, SGS with pressure garments should be used. Second, scar outcomes can vary depending on many factors including scar depth, inflammatory responses, and skin types. We also believe that if we carried out two separate studies, with each study using only one silicone product, the results would have been clearer in relation to patient compliance. With two types of silicone products used in our study, scar outcome results in relation to patient compliance may be somewhat less obvious. Lastly, it would have been ideal to compare the results of two identical scars in the same person, thereby being free from bias and producing higher quality results. However, in practice it was not easy to find two scars that are completely same in one person. Instead, we used a comparison group which did not have statistically significant differences in age, sex, mode of injury, and HS types to evaluate the outcomes. In this point of view, we believe that this study produced optimal results. Nevertheless, more controlled and precise future studies with a larger number should be conducted to further validate our results.
In conclusion, scar outcomes according to silicone product use compliance were assessed by the VSS (an objective index assessed by physicians) and the VAS (a subjective index reported by patients). VSS results displayed worsened pigmentation and height in patients who applied silicone products for less than 3 days per week, especially in the TSG group. Patients who applied silicone products for more than 4 days per week showed significant improvements in all factors, especially in subgroup 3, who applied the products 7 days per week. This result supports that silicone-based products should be applied at least 4–6 days per week. VAS results demonstrated improvements in scar height, pigmentation, and hardness as application time increased. Pain and itching improved regardless of application time.
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