First-Row Transition Metal-Catalyzed Dehydrogenation Reactions

Whether exercising outdoors or spending a day on the beach, the skin is exposed to ultraviolet (UV) radiation from the sun. Even though sunlight has benefits for the human body, overexposure to UV radiation can cause various types of damage to the skin. Sunscreen application is a common practical solution for the protection of skin against UV radiation. To provide long-lasting UV protection after application, the sunscreen should properly bind to the skin and resist removal by different real-life activities, such as wearing clothes, bathing, toweling, swimming, and sweating. Sweating occurs in many situations in which people use sunscreen. However, the interaction of sunscreen and sweat is largely overlooked, likely owing to the inevitable challenges associated with performing in vivo sweat resistance tests and the lack of suitable instrumentation for in vitro studies. This PhD project aimed to develop specific in vitro setups to mimic human skin perspiration, and then to obtain general information on the impact of sweating on sunscreen substantivity, to evaluate the effect of different parameters on sunscreen failure mechanisms during sweating, and to explore methods to develop sunscreen formulations with improved sweat resistance. The results showed that sweating negatively affected sunscreen substantivity and UV protection through wash-off and redistribution of the sunscreen film. Further, two approaches for increasing the sweat resistance of sunscreen were investigated: manipulation of the concentration of hydrophobic film-formers and incorporation of water-absorbing particles in the sunscreen formulation. The results indicated that the combination of moderate concentrations of a hydrophobic film-former and water-absorbing particles capable of forming a gel-like structure in contact with water could successfully increase the film integrity of sunscreen and control the sunscreen wash-off and redistribution.