## 4 Discussion  
Spreading properties are determined by, among others, chemical structure, molecular weight, and consistency of the embollent, and provide information about the lubricating nature of the system, which is an important factor when selecting the appropriate embollent for the preparation being developed. In the case of preparations, such as care oils intended for use on large body surfaces, the embollents used should have a high ability to spread on the skin. The process of spreading emollients is influenced by their physicochemical properties such as viscosity, density, contact angle, and surface tension. Based on the obtained research results, it was shown that the analyzed semi-synthetic and synthetic emollients are characterized by a wide viscosity range (from approximately 21 to 114 mPa-s) compared to natural emollients (from approximately 73 to 112 mPa-s). In their work, [PERSON] et al. [4] found that viscosity is the variable that seems to be the most reliable and effective in predicting the spread of the product on the skin. Moreover, they showed that the spreadability values of silicones, minerals, and vegetable oils are influenced, in addition to viscosity, by both surface tension and density. This study showed that vegetable oils are characterized by higher surface tension and density results compared to the results obtained for synthetic emollients. Similar results were obtained by [PERSON] et al. [4], who claimed that vegetable oils have higher surface tension than silicones, mineral oils, and esters. However, [PERSON] and [PERSON] [35] tested four emollients as branched esters. They found that distribution values depended on molecular weight, viscosity, and chemical structure. Furthermore, they showed that the higher the viscosity, the lower the spreading values. They also found that more polar esters showed lower surface-tension values. This is in accordance with the literature data characterizing the ability to distribute synthetic emollients (Table 1). Dicaprylyl Carbonate, with low viscosity and at the same time the lowest surface tension value, has a spreading capacity of 1600 mm\({}^{2}\)/10 min and belongs to embollients with a very high spreading capacity, Dibutyl Adipate, with a value of 1000 mm\({}^{2}\)/10 min, is classified as a raw material with high spreading capacity, and Octyldodecanol 600 mm\({}^{2}\)/10 min and Caprylic/Capric Triglyceride 550 mm\({}^{2}\)/10 min are classified as medium spreading capacity. Moreover, [PERSON] et al. [50] examined the physicochemical properties, i.e., dynamic viscosity, contact angle, and surface tension of vegetable oils. These were liquids of various viscosities, of which evening primrose oil had the lowest viscosity and milk thistle oil had the highest. According to [PERSON] et al. [51] and [PERSON] [52], these differences result from the content of saturated fatty acids in their composition. Above 16%, an increase in oil viscosity is observed. Milk thistle oil, with the highest viscosity, contains approximately 19% saturated fatty acids, while evening primrose oil only 8%. The different viscosities of the oils translate into their ability to spread on the skin. The low surface-tension values (32-33 mN/m) and low contact angle (of the order of 50\({}^{\circ}\)) of the tested oils confirmed that, for example, borage and evening primrose oils were characterized by good distribution on human skin. In the case of the vegetable oils used in this study, the content of saturated fatty acids varied and was (Table 2) for Macadamia Terrifolia Seed Oil approx. 18% (the presence of acids such as palmitic acid, stearic acid, and arachidonic acid), Prunus Amygdalus Dulcis (Sweet Almond) Oil approx. 11.5% (presence of acids such as palmitic acid and stearic acid), Ricinus Communis (Castor) Seed Oil approx. 5.5% (presence of acids such as palmitic acid and stearic acid), and for Vitis Vinifera (Grape) Seed Oil approx. 20% (presence of acids such as palmitic acid and stearic acid).