In this scoping review, we identified six randomized-controlled trials and a non-randomized-controlled trial on foot skin care for patients with diabetes, all of which were published between 2011 and 2024. Based on our findings, we recommend applying a moisturizer, especially a cream containing urea, or a cream containing 15% glycerol, liquid and 10% soft paraffin twice a day for at least two weeks for dry skin. However, there were no studies on skin care that utilized the occurrence of diabetes-related foot ulcer as an outcome.

In general, moisturizers restore skin hydration through mechanisms of occlusion, humectancy, hydrophilic matrices, and photoprotection [26]. Moisturizer formulations include creams, lotions, ointments, and serums, with creams and ointments, which are especially used for the feet. Ointments are anhydrous semisolid preparations composed of fats, waxes, animal and plant oils, and hydrocarbons, and they are also waterproof. However, these possess poor esthetics, because they are sticky and have a tendency to stain clothing. In contrast, creams are emulsions containing hydrophilic and hydrophobic ingredients, with oil-in-water emulsions the most popular for moisturizer use. Cream-type moisturizers were evaluated in all of the studies reviewed in the present study.

In addition, moisturizing ingredients include petrolatum, silicone, ceramides, fatty acids, lipid trilayers, and natural moisturizing factors such as urea, and lactic acid [26]. In most studies, dry skin improved not only in conjunction with the moisturizer tested, but also in the controls. These results may indicate that applying some kind of moisturizer may be effective in treating dry feet in patients with diabetes. This review also found that only creams containing 5% urea, arginine and carnosine [24], cream containing 10% glycerine, 5% urea, 1% lactic acid, and 8% paraffin [25], and cream containing 15% glycerol, liquid, and 10% soft paraffin, [23] showed an effect as compared to that observed in the controls. By forming a lipid layer on the skin surface, glycerine and paraffin help to improve skin barrier function and prevent dehydration, thereby reducing transepidermal water loss [25]. In contrast, glycerine, urea, and lactic acid are part of a natural moisturizing factor, which is a group of water-soluble substances that are responsible for maintaining water within the keratinized epidermal layers of the skin. Urea functions as a natural endogenous humectant by replacing water in low humidity conditions and maintaining a fluidic stratum corneum [27]. The properties of urea are concentration-dependent, with moisturizing effects observed at 5%, with a desquamation action at 20% and keratolytic action at 40% [25]. Lactic acid is a hygroscopic water-soluble compound characterized by its high water-capturing ability and excellent substantivity on cutaneous proteins, thereby enabling a long-lasting efficacy. In the experiment that utilized urea, arginine and carnosine-based cream, the effect of urea and carnosine on advanced glycosylation end products, the increase in skin hydration due to increased aquaporin synthesis by urea, and the improvement of the microcirculation by arginine were all considered to be the factors that improved dry skin [24]. Thus, if greater effectiveness is required, the use of moisturizers containing these ingredients would be recommended.

While most of the verified application conditions were performed twice a day, and the longest usage period was 42 days, there was no verification conducted that compared the frequency of the application. Thus, more effective care methods could potentially be discovered by further verifying the frequency of the application. Moreover, although it is recommended that these applications be performed for more than 2 weeks based on the previous reports that the beneficial effect appears after about 14 days, this recommendation appears to be based on naturally occurring changes, as the average turnover of fully keratinized cells in normal human epidermis is 14 days [28]. Therefore, the long-term effects and adverse events that occur after 42 days remain unknown and will need to be verified in future studies. On the other hand, considering the mechanism of epidermal turnover, the continuity of foot skin care will undoubtedly affect outcomes. Factors related to the continuity of foot skin care, such as usability and cost, will also need to be investigated in the future.

While the present review evaluated the previous studies that examined several moisturizers, we did not find any previous studies that examined cleansers alone. Although cleansers that aim to have moisturizing effects have also been developed, future studies will need to be conducted to definitively evaluate their effectiveness.

To obtain a broad range of knowledge on this subject, this review included papers that analyzed data on subjects without diabetes [20] and evaluations on subjects that involved areas other than just the foot [21]. Regarding the effects of cleansers and moisturizers containing ceramides, and creams with different pH levels, it cannot be denied that different results could potentially be obtained when the research is limited to only the feet of patients with diabetes. The cleansers and moisturizers covered in this review contain multiple active ingredients, and the results of this review do not definitively prove the effectiveness of any particular ingredient or base materials. The focus of this review was only on cleansing and moisturizing. In addition to these, the prevention of diabetes-related foot ulcers also requires self-care such as foot inspections, nail cutting, not using chemical agents or plasters to remove callus and the avoidance of walking barefoot or in only socks or in thin-soled slippers, in addition to the avoidance of wearing tight socks [16]. However, this review did not specifically evaluate these areas.

This review included only seven studies, and none of them specifically examined long-term effects, so it was not possible to suggest any effective long-term foot skin care methods. More research is needed, especially those that involve long-term foot skin care interventions.