Proteine in peptide uvrščamo v pomembno skupino kozmetično aktivnih sestavin. Njihovi učinki na kožo so raznoliki, od vlaženja, protimikrobne zaščite, hkrati pa posnemajo delovanje naravno prisotnih proteinov kože, zlasti kolagena in elastina. Ena izmed surovin s pomembno vsebnostjo proteinov je tudi sirotka, ki je dolgo veljala za odpadek, ki nastane kot stranski produkt pri predelavi mleka v sir, danes pa se s pridom izkorišča v različnih industrijskih panogah. V kozmetičnih formulacijah, najpogosteje v šamponih, balzamih, čistilnih losjonih in gelih, se uporablja za stabilizacijo emulzij in pen, tvorbo filmov, za vezavo vode in kot tvorilec gela. Sirotko velja izpostaviti kot vir kozmetično aktivnih sestavin za nego kože in las oz. lasišča zaradi bogate vsebnosti proteinov, kot so β-laktoglobulin, α-laktalbumin, imunoglobulin ter številnih drugih skupin. V diplomski nalogi smo razvili in optimizirali dve kozmetični formulaciji z vgrajeno sirotko, in sicer hidrogela za čiščenje obraza, ki sta se razlikovala glede na vrsto uporabljenega zgoščevala, tj. ksantan oz. karbomer. V začetni fazi razvoja smo določili optimalni koncentraciji ksantana in karbomera ter temu prilagodili ustrezno količino decil glukozida, ki deluje kot površinsko aktivna snov. V naslednji fazi je sledilo določanje ustreznega deleža sirotke, in sicer smo želeli vgraditi čim večjo količino le te, brez neugodnega vpliva na fizikalno-kemijske in organoleptične lastnosti formulacij. V zadnjem delu naloge smo tri izbrane formulacije hidrogelov (30 % sirotke, 1,5 % ksantana, 10 % decil glukozida 15 % sirotke, 1 % karbomera, 10 % decil glukozida in 30 % sirotke, 1 % karbomera, 10 % decil glukozida), ki so ustrezale kriterijem organoleptičnih lastnosti, viskoznosti ter pH vrednosti, izpostavili stabilnostni študiji, ta je vključevala testiranje vzorcev shranjenih na sobni temperaturi (25 °C) ter na povišani temperaturi (40 °C). V vnaprej določenih časovnih točkah smo testiranim vzorcem vrednotili viskoznost, pH in organoleptične lastnosti. V okviru 42-dnevne stabilnostne študije smo ugotovili, da ima sirotka največji vpliv na organoleptične lastnosti izdelkov, tj. na spremembo barve in vonja. Zaključimo lahko, da so vsi trije vzorci s sirotko kemijsko (pH, organoleptične lastnosti) stabilni, ne glede na vrsto polimera kot zgoščevala. Rezultate bi bilo smiselno nadgraditi v okviru dolgoročnih stabilnostnih študij, predstavljajo pa dobro izhodišče za razvoj kakovostnih kozmetičnih izdelkov na osnovi sirotke. Proteins and peptides are an important group of cosmetically active ingredients. Their effects on the skin are diverse, ranging from moisturising, antimicrobial protection and mimicking the action of naturally occurring skin proteins, in particular collagen and elastin. One of the raw materials with an important protein content is whey, which was long considered to be a waste by-product of the processing of milk into cheese, but is nowadays used to great advantage in various industries. In cosmetic formulations, most commonly in shampoos, conditioners, cleansing lotions and gels, it is used to stabilise emulsions and foams, to form films, to bind water and as a gel-forming agent. Whey should be highlighted as a source of cosmetically active ingredients for skin and hair or scalp care due to its rich content of proteins such as β-lactoglobulin, α-lactalbumin, immunoglobulin and many others. In the diploma thesis, we developed and optimised two cosmetic formulations with incorporated whey, namely hydrogels for facial cleansing, which differed according to the type of thickener used, i.e. xanthan or carbomer. In the initial phase of development, the optimum concentrations of xanthan and carbomer were determined and the corresponding amount of decyl glucoside, which acts as a surfactant, was adjusted accordingly. The next stage was to determine the appropriate proportion of whey, with the aim of incorporating as much whey as possible without adversely affecting the physico-chemical and organoleptic properties of the formulations. In the last part of the task, three selected hydrogel formulations (30 % whey, 1,5 % xanthan, 10 % decyl glucoside) were prepared 15 % whey, 1 % carbomer, 10 % decyl glucoside and 30 % whey, 1 % carbomer, 10 % decyl glucoside), which met the criteria of organoleptic properties, viscosity and pH value, were subjected to a stability study, which involved testing samples stored at room temperature (25 °C) and at elevated temperature (40 °C). At predetermined time points, the viscosity, pH and organoleptic properties of the tested samples were evaluated. In the 42-day stability study, whey was found to have the greatest influence on the organoleptic properties of the products, i.e. colour and odour changes. It can be concluded that all three samples with whey are chemically stable (pH, organoleptic properties), irrespective of the type of polymer as thickener. The results should be further developed in the context of long-term stability studies and represent a good starting point for the development of quality cosmetic products based on whey.