Cosmetics for Sensitive Skin: Assessing Rheological Properties, Stability, and Safety

Abstract

Skin compatibility is a common issue and can often be worsened by certain ingredients in cosmetics. This is why developing well-balanced and -tolerated formulas is now an essential challenge. In this work we developed a cream rich in antioxidant, soothing, and moisturizing agents complying with concentration limits for sensitive skin. An initial optimization was carried out, and the best-performing formula was fully characterized to test its rheological properties under static or dynamic conditions and product safety. The formulation proved to be highly stable even under thermal stress, as shown by Turbiscan Lab analyses, which reported backscattering values ±2. Rheological tests also indicated a solid-like behavior with reduced viscosity at skin temperature of 32 °C, confirming the good spreadability of the cream. Finally, in vivo tests on healthy volunteers showed excellent safety results and good overall appreciation of the product. No changes in transepidermal water loss (7.9 ± 3.5 vs. 5.5 ± 0.4, p > 0.05), skin hydration (44.2 ± 18.6 vs. 50.5 ± 14.1, p > 0.05), or color were detected within 6 h from application, compared with baseline values. Moreover, volunteers highlighted the cream’s suitability for dry skin and expressed satisfaction with spreadability, a nourishing and hydrating sensation after application, and the absence of residues, consistently rating them ≥4 in the skin feeling questionnaire. These results are promising and support the potential use of the product on sensitive skin.

1. Introduction

Sensitive skin is recognized as a widespread condition, although prevalence estimates differ considerably among studies. Population surveys consistently show that about 60–70% of women and roughly half of men report experiencing skin sensitivity [1,2]. From a clinical point of view, sensitive skin is described as a hyper-reactive condition in which individuals experience unpleasant sensations such as stinging, burning, or tingling in response to stimuli that should not normally provoke irritation [3]. These conditions represent a major concern not only for dermatology but also for the cosmetic industry, given their high prevalence, their impact on quality of life, and increasing consumer demand for specialized skincare products.

The pathophysiology of sensitive skin is multifactorial. Intrinsic factors such as chronological aging, hormonal changes, or genetic predisposition play a role in weakening the cutaneous barrier and altering epidermal lipid metabolism [4]. Extrinsic contributors include climatic stress (low humidity, temperature changes, UV exposure), mechanical or chemical irritants (detergents, surfactants, pollutants), and inappropriate cosmetic products [5]. Sensitive skin responds to these stimuli with specific alterations, such as increased transepidermal water loss and reduced natural moisturizing factor content [6], promoting a dangerous increased freedom in skin penetration of irritants and allergens.

This complexity underscores the necessity for cosmetic formulations that not only restore hydration but also respect the delicate equilibrium of the skin barrier and minimize the risk of irritation.

Formulating cosmetic products for sensitive skin faces several challenges. In this case, the selected excipients must be characterized by high biocompatibility, hypoallergenicity, and, above all, absence of potential irritants. Generally, excipients such as aggressive sulfites, surfactants, or certain preservatives should be excluded [7,8,9]. Emulsifiers and stabilizers must be carefully chosen to achieve formulation stability without compromising tolerability, considering that maintaining formulation stability over time is crucial. Instabilities such as phase separation, crystallization, or microbial contamination not only reduce efficacy but may also enhance the risk of irritation. Moreover, product texture and sensorial properties are critical. Subjects with sensitive skin are often more demanding in terms of sensory acceptance: formulations must spread easily, absorb quickly, and leave a non-irritating film. These attributes are closely linked to the rheological behavior of the product, which governs spreadability, consistency, and perceived skin feel.

In this context, the present study aimed to design and optimize emulsion-based cosmetic formulations tailored for individuals with sensitive skin. Starting from base formulations, progressive modifications were introduced to improve microstructural stability, rheological behavior, and pH compatibility with the physiological range of the skin. The formulations underwent accelerated stability testing under controlled conditions, as well as detailed micro-rheological and dynamic rheological analyses to evaluate their viscoelastic properties. Finally, in vivo testing on human volunteers was carried out to establish the safety and tolerability profile of the optimized formulations. By integrating technological, physicochemical, and clinical assessments, this study aims to provide a comprehensive evaluation of dermocosmetic formulations for fragile skin types. Unlike previous studies mainly focused on single ingredients or limited endpoints, our work highlights the importance of evaluating the overall formulation by providing data of stability and rheology directly relevant to the safety of the cosmetic.

This multidisciplinary approach may inform future strategies in cosmetic science, fostering innovation in the development of dermocosmetic products targeted to populations with increased susceptibility to cutaneous sensitivity.

2. Materials and Methods

2.1. Materials

Prunus amygdalus dulcis oil (sweet almond oil USP), jojoba oil (jojoba oil DAC), argania spinosa kernel oil (argan oil), cetyl/stearyl alcohol (Ceteareth-25), isopropyl myristate (Acemoll^® L), caprylic/capric triglyceride (tegosoft^® CT), cetyl palmitate (artifical cetaceum DAB-Ph. Eur.), shea butter (karité butter), beeswax (cera alba), urea (carbamidium USP), paraffin, panthenol (D-panthenol USP), allantoin (allantoin USP grade), xanthan gum (xanthan gum Ph. Eur. -USP), hydroxyethyl cellulose (natrosol HR), and phenoxyethanol (acnibio PE 9010) were purchased from A.C.E.F. (Piacenza, Italy). Tocopheryl acetate (dl-α-tocopherol acetate) was provided by Roche (Milan, Italy). Glycerol (vegetal glycerin) was supplied by Sigma Aldrich (Merck KGaA, Darmstadt, Germany).

2.2. Preparation of Emulsions

Initially, four prototype formulations were prepared based on a formulation for dry skin suitable for xerosis, previously described in the Formulario Nacional of the Real Farmacopea Espanola, with some modifications in composition and preparation method [10]. More specifically, two different phases were prepared: a hydrophilic phase A and a lipophilic phase B. Both phases were heated to 60 ± 5 °C and then mixed using Topitec^® (WEPA Apothekenbedarf GmbH & Co. KG, Hillscheid, Germany), a dermatological mixing system. The compositions of the prototype formulations are presented as follows: Formulations F1 and F2 contain liquid paraffin (56% w/w), cetyl palmitate (12.5% w/w), urea (7% w/w), beeswax (F1: 12% w/w; F2: 6% w/w), and MilliQ water (q.s. to 100 g). Formulations F3 and F4 were prepared through the addition of tocopheryl acetate in the oil phase of formulations F1 and F2, respectively.

Next, the optimization of formulations and advanced characterization were carried out by preparing a new hydrophilic and lipophilic phase, both heated to 70 °C under slow stirring using a magnetic plate (AM4 Digital PRO, VELP Scientifica, Usmate, MB, Italy) and then mixed by the high-shear homogenizer Silverson^® L5M-A (Ghiaroni & C. Srl, Milan, Italy). The heating temperature of 70 °C was required to ensure the complete melting of the solid lipid components of the oil phase, and the same temperature was used for the aqueous phase. The new formulations were developed starting from formulation F2, which proved to be the overall best among the prototypal formulations.

Table 1. Qualitative and quantitative compositions of formulations.

Formulations	Composition (%)
	Cetyl Palmitate	Beeswax	Caprylic/Capric Triglyceride	Xanthan Gum	Tocopheryl Acetate	Sweet Almond Oil	Cetyl/Stearyl Alcohol	Isopropyl Myristate	Shea Butter	Jojoba Oil	Argania Spinosa Kernel Oil	Panthenol	Allantoin	Urea	Phenoxyethanol	Glycerol	Hydroxyethyl Cellulose	MilliQ Water
F2A	12.5	2.5	/	/	4	6	5	5	12	12	6	2	1	7	0.8	3	/	Q.s. to 100
F2B	6	1	6	0.1		4	3.5	4	6	6	4						/
F2C		4	6	0.3													/
F2D		3	6	0.3													0.75

shows all the ingredients of the optimized preparations and the percentages used. Each formulation was stored at room temperature for 24 h to ensure the settling of the cosmetic formulations before starting with analyses [11].

2.3. pH Determination

The pH evaluation was performed using a calibrated benchtop pH meter (Hanna Instruments^®, Padova, Italy). To ensure cutaneous compatibility, a range between 4.5 and 6.5 was considered as acceptable [12]. Formulations not in this range were adjusted using a solution of citric acid 10% w/v during the preparation phase [13]. Each formulation was analyzed at least 3 times, and results are reported as the mean value ± SD.

2.4. Stability Test

Turbiscan Lab^® (Formulaction, L’Union, France) was used to investigate the long-term stability of formulations [14]. Samples were placed into suitable glass vials and analyzed to evaluate any changes in light transmission (ΔT) and backscattering (ΔBS) over time (1 h) and at different temperatures, namely room temperature (25 °C) and elevated stress temperature (40 °C). The Turbiscan Stability Index (TSI) was also calculated as a function of the obtained profiles of ΔT and ΔBS over time to provide a comparison among the different formulations and their tendency to destabilize [15].

2.5. Rheological Studies

The viscoelastic properties of formulations were monitored using a Rheolaser Master ™, based on Diffusion-Wave Spectroscopy measuring any fluctuation in the speckle pattern caused by the Brownian motion of scattering centers in the samples. Each cream was loaded into specific cylindrical glass vials and analyzed at both 25 °C and 40 °C. Data were processed using the software RheoSoft Master 1.4.0.0 to collect information on the mechanical stability of emulsions at rest [16]. The best formulations underwent further studies of dynamic rheological characterization using the rheometer HAAKE MARS (Modular Advanced Rheometer System) 40 (Alfatest, Rome, Italy) equipped with cone–plate geometries (40 mm diameter; 2° angle) [17]. In this case, the evaluations were carried out at room temperature and at simulated skin temperature (32 °C) in order to mimic the real conditions of topical application of the product [18]. Each sample was loaded on the lower plate and kept at rest for 5 min before starting the analyses. Preliminary tests of amplitude sweep were carried out to define the linear viscoelastic region (deformation range: 0.01–100%; frequency: 1 Hz). The rheological studies included the following: viscosity studies considering shear rates from 0.1 s⁻¹ to 100 s⁻¹; an oscillatory frequency sweep test under a maintained shear stress (from 0.1 Hz to 10 Hz; fixed shear stress at 1 Pa) [11].

2.6. In Vivo Studies on Human Volunteers

The cutaneous safety and tolerability of the cosmetic formulation identified as the most promising in the previous studies were assessed through in vivo studies involving six healthy human volunteers (mean age 27 ± 9). Each subject was deeply informed about the aim and risks of participating in the study and signed an informed consent form, thus approving the experimental protocol. Before starting the studies, volunteers were accompanied to a temperature-controlled room (24 ± 1 °C; R.H. 40–50%) for an acclimatization period of 60 min [16]. Two different sites were traced on each forearm of each volunteer, one site for the control (saline solution 0.9% w/v) and one site for the cosmetic to be tested, leaving at least 2 cm of space between sites to avoid interference. Data were collected before application (baseline) and after 1, 3, and 6 h.

Skin hydration and TEWL were calculated through the C + K Multi Probe Adapter (Courage & Khazaka, Cologne, Germany), using the probes Corneometer^® CM 825 and Tewameter^® TM 300 [19,20].

The same scheme of sites was considered for the color analyses to find any changes not detectable to the naked eye after the application of the cosmetic. The Mexameter^® MX 18 probe (Courage & Khazaka electronic GmbH, Köln, Germany) was used to detect melanin and erythema values; finally, the spectrophotometer X-Rite Ci62 (X-Rite Incorporated, Grandville, MI, USA) was used to confirm results. Any changes in the erythematous index (EI) were derived using the following equation:

$$\mathbf{E}\mathbf{I}=100[\mathrm{l}\mathrm{o}\mathrm{g}{\displaystyle \frac{1}{\mathrm{R}560}}+1.5\left(\mathrm{l}\mathrm{o}\mathrm{g}{\displaystyle \frac{1}{\mathrm{R}540}}+\mathrm{l}\mathrm{o}\mathrm{g}{\displaystyle \frac{1}{\mathrm{R}580}}\right)-2\left(\mathrm{l}\mathrm{o}\mathrm{g}{\displaystyle \frac{1}{\mathrm{R}510}}+\mathrm{l}\mathrm{o}\mathrm{g}{\displaystyle \frac{1}{\mathrm{R}610}}\right)]$$

(1)

In this formula, R denotes the reflectance values at selected wavelengths, chosen for their link to the primary skin chromophores, melanin and hemoglobin (510, 540, 580, and 610 nm) [11].

All studies involving human subjects were performed in accordance with the Declaration of Helsinki, and the protocols were approved by the Research Ethics Committee of the “Magna Graecia” University of Catanzaro (Ethics approval number: 392/2019).

2.6.1. Assessment of Skin Sensations

In addition to the instrumental validations, a subjective assessment of skin sensations was conducted using a questionnaire administered to each study participant. The sentences or questions were rated by the volunteers from 0 (completely disagree) to 5 (fully in agreement) and focused on the following: (A) overall acceptance of the study product; (B) spreadability; (C) tactile comfort of the texture; (D) absorption speed; (E) perceived immediate hydration; (F) perceived long-lasting hydration; (G) softness perception; (H) feeling of skin protection; (I) perceived lack of residues; (J) overall acceptance of fragrance; (K) overall feeling after the application; (L) suitability for nighttime use; (M) suitability for daily use; (N) suitability in case of xerosis or very dry skin. These answers contributed to defining the acceptability of the cosmetic and the real usage adherence.

2.7. Statistical Analysis

The statistical analysis was carried out using one-way ANOVA. Post hoc comparisons were performed with Bonferroni’s t-test, considering p ≤ 0.05 as a threshold for statistical significance. Data collected were processed using Sigmaplot v. 12, GraphPad v. 8.4.2 and Excel (Office 2010).

3. Results and Discussion

3.1. Characterization of Formulation Prototypes

The stability of emulsions goes beyond being a simple technical feature; it directly affects both tolerability and performance. This is especially important when dealing with fragile or sensitized skin. A well-stabilized emulsion allows all components to remain evenly dispersed, maintains a steady dose and pH, and limits exposure to free surfactants. As a result, the likelihood of irritation or a more significant skin reaction is reduced [21,22]. Contrarily, when the microstructure of an emulsion is altered, resulting in processes such as creaming, sedimentation, or flocculation, the outcome may be an uneven dosage and a less pleasant user experience. This is particularly dangerous in individuals with sensitive skin, where the risk of adverse reactions is higher [23]. In addition, the rheology of a cosmetic, such as initial viscosity, peak viscosity, and viscosity at high shear rates, is closely linked to both primary and secondary skin sensations, and these parameters need to be carefully considered during primary characterization studies [24]. For this reason, the experimental investigation was designed starting with rheological analysis, considered the primary step toward a comprehensive evaluation of the product. The microstructure of the preparations was initially examined in four prototype formulations, named F1–F4, developed from a base cream for dry skin suitable for xerosis, as described in the National Formulary of the Spanish Pharmacopoeia, with some modification [10], and further enriched with urea and tocopheryl acetate, as reported in Section 2.2 of the Material and Methods Section [25,26]. Urea and tocopheryl acetate were incorporated at carefully selected concentrations in order to take advantage of their respective properties, with urea enhancing hydration and skin barrier function, and tocopheryl acetate providing antioxidant protection [27,28]. Static rheology studies were performed using an advanced light scattering (DWS, diffusing-wave spectroscopy) technique, considered to measure the Brownian motion of the dispersed droplets of the sample [29] at rest, and data were processed using the software RheoSoft Master^® 1.4.0.0. The results for the elasticity index are reported in Figure 1. As can be seen, all formulations exhibited higher elasticity values when analyzed at 25 °C (Figure 1, top) compared to those recorded at 40 °C (Figure 1, bottom), with most curves reaching stabilization after 20–30 min. The relatively high elasticity index observed at 25 °C may be explained by the substantial wax content in the prototype formulations, since these components generally contribute to a more rigid and compact structure [30,31]. In line with the thermal behavior typically observed in waxes, shifting from a more solid to a more pliable state as temperature increases, a reduction in the elasticity index was detected at 40 °C [32]. Specifically, the elasticity index values at 40 °C dropped by roughly one order of magnitude compared with those measured at 25 °C. This decrease reflects a loss of internal structural rigidity, allowing the dispersed droplets within the sample to move more freely [11].

Another study of stability under rising temperatures and at rest was performed using Turbiscan Lab^®, able to record backscattering and transmittance values to detect early signs of instability, well before visible phase separation can be observed by the naked eye [33]. Figure 2 shows variations in backscattering profiles (ΔBS) of formulations F1–F4, indicating good stability for all samples at room temperature (Figure 2A–D). Contrarily, when exposed to high temperatures of 40 °C, mimicking accelerated storage conditions, only F2 maintained acceptable ΔBS within ±2, while the other samples exhibited signs of destabilization, thus reporting ΔBS values within ±7 for formulation A and ±14 for formulations C and D (Figure 2E–H) [34]. Such high variations in BS values may indicate destabilization phenomena, attributable to flocculation or coalescence, depending on the extent of aggregation of the internal droplets of the emulsion [35]. This effect was probably mechanistically linked to the lower content of beeswax and the absence of tocopheryl acetate in F2, factors that may have contributed to maintaining stability at elevated temperatures. In fact, increasing the proportion of wax tends to create more rigid internal networks, which, however, are also more prone to disruption under external stress, thereby increasing susceptibility to thermal disruption [36]. The simultaneous presence of tocopheryl acetate, acting as a lipophilic plasticizer, may contribute to destabilization under these conditions.

Results for stability were further confirmed through the evaluation of kinetic stability profiles of the same samples, calculated as TSI (Turbiscan Stability Index) values. This numerical parameter, derived from ΔT and ΔBS values, is directly associated with the risk of destabilization. Accordingly, lower TSI values indicate greater formulation stability [15]. As shown in Figure S1, formulations F1–F4 reported similar TSI values (lower than 1) at 25 °C, while when they were exposed to extreme temperatures of 40 °C, TSI values increased for all the samples, except for F2, which retained almost the same TSI values.

3.2. Optimization and Further Characterization of Creams

Based on the results derived from prototype formulations, F2 was selected as the starting point for the optimization process to improve consistency and suitability for its use for sensitive skin. Table 1 (Section 2.2) shows the composition of four additional formulations (F2A–F2D) derived from F2. Considering that liquid paraffin is sometimes criticized and perceived negatively, we opted to replace it entirely with a mix of plant-derived oils, i.e., sweet almond oil, jojoba oil, and argan oil, together with shea butter, all of which are generally recognized as safe [12,37]. For the same reason, the proportion of beeswax was drastically reduced and kept within a range of 1% to 3%. The formulations were further enriched with panthenol, well known for its soothing properties, its safety, even on sensitized skin, and its ability to support the recovery of a compromised skin barrier [23,38]. Further components were added during the preparation, such as allantoin, well known for its ability to support skin barrier repair and widely used in cosmetics for sensitive skin, and glycerol, a humectant particularly beneficial in case of sensitive and dry skin [39,40]. The concentrations of urea and tocopheryl acetate used in formulations F1–F4 were kept unchanged. The decision to use tocopheryl acetate, rather than other antioxidants, was based on its favorable balance between tolerability and efficacy, supported by documented stability, a well-established safety profile, and its widespread use in cosmetic formulations [26,41]. Urea was instead selected as a moisturizing agent due to its properties and high level of tolerability [27]. Phenoxyethanol was chosen as the preservative for the optimized formulations because it shows the best tolerability profile in cosmetics, with a broad antimicrobial spectrum and good safety even on sensitive skin when used up to 1% w/w [42]. An initial stability assessment carried out with Turbiscan Lab^® showed that formulations F2A–F2D exhibited optimal ΔBS values both at 25 °C and in extreme conditions of 40 °C. Figure 3 presents the TSI profiles for comparison among F2A–F2D. All samples reported TSI values below 1.5, indicating good stability profiles and a comparable trend, suggesting no relevant differences between them nor variations at increasing temperatures. The similarity of the TSI values also suggests that the differences in composition among the tested formulations did not translate into relevant measurable variations in stability, even when the temperature was increased.

3.3. Analysis of pH Values

Maintaining the skin surface at a pH close to its physiological range supports both barrier integrity and the balance of the microbiota. This is particularly relevant in individuals with reactive skin, where the pH is typically elevated by about 0.2–0.3 units compared to normal skin values [43]. For this reason, pH values of each formulation were calculated and are reported in

Table 2. Results of pH measurements on formulations F2A–F2D. Data are reported as the mean value ± SD.

Formulation	pH
F2A	6.66 ± 0.12
F2B	7.14 ± 0.28
F2C	7.11 ± 0.31
F2D	6.72 ± 0.21

. All the samples with pH values outside the range between 4.5 and 6.5 were adjusted during the preparation by adding an appropriate amount of citric acid solution (10% w/v). They were analyzed again using Turbiscan Lab^® to confirm their stability following the addition (Figure S2), and the resulting profiles (TSI < 2) were consistent with those shown in Figure 3 [12,13].

3.4. Assessment of Rheological Features of Optimized Formulations

Samples F2A–F2D were further characterized for their rheological behavior using the Rheolaser Master. The monitoring of the elasticity index over time and temperatures is shown in Figure 4. As can be seen, at 25 °C, formulation F2D showed the most favorable elastic properties, reaching stability within a few minutes. When the temperature was increased at 40 °C, formulations F2A–F2C reported a slight reduction in elasticity index values, while maintaining the same overall trend (F2A < F2B < F2C). Formulation F2D also recorded the highest elasticity index at 40 °C, although with faster growth kinetics at the higher temperature before stabilizing at the maximum value. The behavior observed for formulation F2D may be related to the presence of hydroxyethyl cellulose in its composition. This polymer, well known for its structuring and thickening properties, likely promotes the formation of a more robust network, thus enhancing the elasticity of the formulation even under changing temperature conditions [44,45].

Viscoelastic investigation into cosmetic products gives information about fundamental aspects, such as spreadability and consistency as a function of temperature [46]. In the case of sensitive skin, the cosmetic applied must be soft and must not induce irritation or friction on the skin, and dynamic rheological measurements could help to predict the response of cosmetic products during production procedures and skin application [47]. Given its more favorable structural profile compared to the other tested formulations, along with its superior macroscopic features, such as its more uniform consistency and suitability for the intended use, formulation F2D was further investigated through dynamic rheology studies. Indeed, formulation F2D exhibited the most favorable elasticity index among the tested formulations and reached a superior elasticity index after 10 min, also when temperature increased from 25 °C to 40 °C. The results, supported by rheological analysis, provide a numerical basis for the choice of F2D over the other formulations, as a greater elasticity index is often related to a more organized and resistant structural network, which is typical of more stable emulsions [48].

The formulation F2D is an O/W emulsion defined by the hydrophilic Ceteareth-25; waxes and esters add viscosity and consistency to the preparation. As shown in Figure 5A, at both room temperature (25 °C) and simulated skin temperature (32 °C), the values of G′ exceeded G″, indicating a predominantly elastic, “solid-like” behavior and confirming good structural stability [49]. Figure 5B reports the apparent viscosity of formulation F2D as a function of shear rate (s⁻¹) at both 25 °C and 32 °C. In both conditions, a shear-thinning profile was observed, with viscosity decreasing as the applied shear increased. At 32 °C, a slight reduction in viscosity compared to 25 °C was noted. Interestingly, this behavior may be advantageous for the spreadability of the cosmetic, particularly on compromised skin, as the product could appear softer and easier to apply [50].

3.5. In Vivo Evaluation

Confirming the skin tolerability of a topical formulation is an essential requirement, and it becomes even more critical when the formulation is intended for fragile skin. Under such conditions, the skin is indeed more exposed and prone to adverse reactions, making it necessary to ensure that the formulation is completely non-toxic. To achieve this, the formulation was designed to prioritize soothing, moisturizing, and re-epithelizing ingredients, while avoiding potentially irritating components such as fragrances, harsh surfactants, and aggressive preservatives [51]. Preliminary evidence on tolerability was recorded through in vivo tests carried out on the skin of healthy human volunteers (number of volunteers = 6). As shown in Figure 6, formulation F2D maintained skin hydration levels within 6 h of application (Figure 6A), reporting no significant differences compared to baseline values at time zero (44.2 ± 18.6 vs. 50.5 ± 14.1, p > 0.05), similar to data recorded with saline solution used as the control (47.6 ± 22.4 vs. 45.8 ± 13.6, p > 0.05). In addition, the application of the formulation preserved TEWL values compared to baseline (7.9 ± 3.5 vs. 5.5 ± 0.4, p > 0.05) (Figure 6B), thus supporting high levels of safety in healthy volunteers and the ability to retain skin barrier integrity [52]. A slight but not significant reduction in TEWL values was observed within 6 h from the application of the cosmetic. However, the short observation period does not allow definitive conclusions to be drawn regarding the potential long-term benefits of formulation F2D. Extended clinical evaluation will therefore be required to clarify this aspect. Nevertheless, the absence of alterations in baseline values is a positive finding, as it excludes the possibility of an immediate disruption of the skin barrier and suggests a potential beneficial reduction in TEWL.

Another key parameter in assessing the safety of a cosmetic is the evaluation of possible colorimetric changes occurring on the skin after the application of the product, and these may correlate with irritation phenomena or other adverse reactions that are not visible to the naked eye [53]. For this reason, any change in cutaneous skin color was assessed, but no significant differences (p > 0.05) were observed compared to baseline values for melanin and erythema values (Figure S3A and S3B, respectively). The absence of significant changes also confirmed the lack of a whitening effect following the application, an important factor for product appeal and consumer acceptance.

These findings were further supported by reflectance spectroscopy analyses (Figure 7), reporting erythema index values over time, following the application of formulation F2D. As can be seen in the Figure 7, values remained stable within 6 h from the application, showing only minor and not significant (p > 0.05) variations, comparable to those observed with saline solution used as the control. These results confirmed the absence of irritant effects and reinforced the favorable safety profile of formulation F2D on healthy volunteers.

3.5.1. Skin Feeling Test

The acceptance of formulation F2D was further supported by the results of the sensory evaluation test (Figure 8). The questionnaire was completed by the volunteers who participated in the in vivo study, and they were asked to rate each item/statement (A–N) on a scale from 1 (strongly disagree) to 5 (strongly agree).

As can be seen in Figure 8, all the volunteers recognized the suitability of formulation F2D for application to compromised/dry skin, indicating their full agreement with question N. Given the rich and dense texture of the tested formulation, most volunteers indicated a preference for evening/night use rather than daytime application (questions L and M, respectively), although they gave a score greater than 4 in response to the question concerning the absence of unpleasant cream residues (question I). This indicated that the application was not perceived as unpleasant, despite the rich consistency of the product, which had been designed to provide nourishment to compromised and dry skin. Also, the tactile comfort (question C), the absorption speed (question D), and the overall feeling following the application (question K) were rated positively, with average scores close to 4, confirming the good cosmetic acceptability of the formulation. The olfactory acceptance (question J) received an average score of 3.3, with generally neutral evaluation by the volunteers. This outcome was likely related to the absence of fragrance, a feature considered appropriate for formulations intended for damaged skin, as fragrances are often associated with allergic effects [54]. The cream, formulation F2D, also received scores ≥ 4 for overall application acceptance (question A), spreadability (question B), perception of both immediate and long-lasting hydration (questions E and F, respectively), post-application skin softness (question G), and the feeling of protection (question H). These findings indicate a high level of cosmetic acceptability even on skin not affected by damage.

4. Conclusions

In this study, we developed and technically validated a new cosmetic preparation. The absence of ingredients considered harmful to sensitive skin and the inclusion of components such as tocopheryl acetate as an antioxidant and soothing agent and urea as a humectant agent made it possible to formulate a cosmetic product specifically designed for the needs of dry and sensitized skin. After an initial optimization phase, the cream F2D was subjected to an in-depth chemical–physical and technological formulation characterization, reporting good stability both at room temperature (25 °C) and in extreme storage conditions (40 °C), as demonstrated by Turbiscan Lab analyses. Further dynamic rheology studies were performed on the cream at room temperature and cutaneous temperature (32 °C). In both cases, a solid-like behavior (G′ > G″) and a reduction in viscosity as the shear rate increased were reported, an advantageous aspect for the product’s spreadability. Particular attention was paid to in vivo evaluation of the cosmetic preparation’s safety on healthy volunteers. The tests demonstrated unchanged TEWL, hydration, colorimetric parameters, and erythematous index values within 6 h from the topical application of the cream, proving the preparation’s safety on healthy volunteers. The volunteers’ feedback also confirmed the overall acceptability, sensation of hydration, and suitability for very dry skin, reporting ratings ≥ 4. Although preliminary results are promising, further in vivo studies should be performed on sensitive skin to confirm the real safety and tolerability of the cream F2D for the intended target.