## 4 Discussion  
Although many collagen products, such as drinks, tablets/capsules, and cosmetics, have been developed in the foods and cosmetics industries recently, the buccal delivery technology that is applied to collagen peptide delivery is unique. Collagen products have usually faced absorption issues because (i) when they are taken orally, the polypeptide is broken down by digestive enzymes, and (ii) when it is applied on the skin's surface in the form of cosmetics, the collagen polymer cannot efficiently permeate the skin surface. Therefore, new technology for enhancing the absorption of collagen peptides is needed. The buccal permeation results suggest the possibility of improving collagen peptide absorption without breaking the peptide. [PERSON] et al. investigated hydrophilic polymer-based buccal films containing 2-3 kDa of collagen hydrolysate, finding that they can permeate mucosa via an in vitro human buccal tissue permeation test [13]. A concentration of 300 \(\mathrm{\mu g/cm^{2}}\) of collagen hydrolysate was detected in permeated human buccal tissues after 4 h in their study. The permeation results in our study are in good agreement with [PERSON] et al. 's study. We demonstrated that the small molecular weight of the collagen peptide facilitated easier penetration through buccal tissues compared to a large peptide. The film method is more efficient than taking a capsule, tablet, or drink because the collagen peptide can permeate directly through the buccal mucosa; however, collagen taken orally needs to be digested and absorbed again. Many systematic reviews on the effectiveness of oral collagen supplementation have recently confirmed that they can enhance skin moisture, elasticity, and roughness [21]. The effects of collagen peptide use on skin hydration were already reported in previous studies. [PERSON] et al. found that the skin moisture of subjects taking 10 mg/d of collagen was significantly higher than those taking 0.5 mg/d of collagen after 8 weeks, with 30.99 \(\pm\) 16.78% for high intake and 18.79 \(\pm\) 12.85% for low intake [26]. In addition, skin hydration among woman volunteers significantly increased by 16% after daily oral intake of 10 g of collagen for 4 weeks compared with the placebo group [27]. The R2 skin elasticity significantly improved from 0.69 \(\pm\) 0.05 at 0 weeks to 0.71 \(\pm\) 0.06 at 12 weeks in the test group, which drunk 2.5 g/d of collagen peptide [21]. [PERSON] et al. induced the skin elasticity (R2) of volunteers taking a collagen capsule containing 10 mg collagen per day, and they found significant enhancement on the cheek after 4 weeks (25.67 \(\pm\) 23.55%) and canthus after 8 weeks (20.84 \(\pm\) 10.75%) [26]. Compared to a placebo, a significant decrease in skin wrinkle depth was seen in the test group, which took a drink product every day for 3 months and procollagen type I containing 2.5 g of collagen every day for 56 days [21; 28; 29]. In addition, [PERSON] reported that a daily oral intake of 10 g collagen for 12 weeks led to a significant reduction in collagen network fragmentation [27]. This study was conducted as a clinical trial with 43 healthy women who consumed either a placebo (n = 21) or functional supplement (n = 22) for 4 weeks. An improvement of human skin treated with the buccal delivery collagen peptide film was demonstrated. Although the effectiveness of collagen taken orally, such as capsules and drinks, on skin improvement was good in various studies, the collagen peptide film has only been tested in this study, and positive effects were shown. Most former studies on other oral collagen products report human skin improvement after 4, 8, and 12 weeks [21; 26; 27; 28; 29]. However, buccal delivery of the collagen peptide film showed effects after 2 weeks. In addition, the wrinkles on the cheeks of volunteers were reduced by the collagen buccal film after 2 weeks. Thus, using buccal delivery technology for skin enhancement was more efficient than other oral products, such as tablets/capsules and drinks.