SUN CARE 53
Photostabilisation: for safe, pleasant sunscreens
n Fiona Feng, Dennis Zlotnik, Eileen Zhang – Hallstar, US
Sunlight, including ultraviolet radiation, provides the energy necessary to sustain life on Earth. The solar energy reaching the Earth’s surface at sea level consists of non-ionising radiation spanning wavelengths of 290-3000 nm. This non-ionising radiation contains infrared radiation (~ 50%), visible light (~ 40%), and ultraviolet radiation (~ 10%). Ultraviolet radiation (UVR) is the solar spectrum of wavelengths between 100 and 400 nm, and it is invisible to human eyes. UVR is categorised into UVA (320-400 nm), UVB (290-320 nm), and UVC (100-290 nm), with UVC rays being unable to reach the Earth’s surface. Terrestrial UVR levels change according to natural conditions such as the season, latitude, altitude, atmospheric effects, and the angle of the sun’s rays through the atmosphere as defined by the solar zenith angle. Due to UVB’s shorter wavelengths, these factors have a much more pronounced effect on daily terrestrial UVB levels than on UVA levels. For instance, cloud cover can reduce UVB radiation by 15%-30%, and air pollution can reduce UVB levels up to 20% by absorbing, scattering and reflecting UVB rays. In contrast, the atmosphere filters out little UVA, and its intensity remains relatively constant throughout the day. Consequently, the ratio of UVA intensity to UVB intensity can vary from 120:1 in the morning and evening to 5:1 at noon.
UVR can be both beneficial and harmful to the human body. Certain doses of UVR are required to produce vitamin D, which is critical to many basic human functions. Appropriate doses and types of UVR can also provide therapeutic improvements to some skin disorders. However, both long and short-term exposure to UVR can also cause a variety of detrimental biological effects such as sunburns, photoageing, and skin cancer in humans.
The thick outer layers of the epidermis
offer a natural defence against UVR by absorbing or reflecting 90%-95% of incidental UVB. But UVA, with its longer wavelengths, can penetrate the skin more deeply than UVB and can more easily reach the proliferative basal layers of the
November 2018 Abstract
During the photostabilisation process, the excited state energy of a light-absorbing species is removed by energy transfer and/or by an electron transfer quenching mechanism. By thus returning it to its ground state, photostabilisation stabilises the light-absorbing species, which prevents its photodegradation and the generation of reactive oxygen species (ROS). Hallstar has pioneered photostabilisation technology to promote effective sun protection and comprehensive photoageing prevention. Our photostabilisers for UV filters protect photolabile UV filters from decomposition and shield photosensitive UV filters from generating ROS. A paradigm shift from UV filter protection resulted in the development of our revolutionary anti-ageing technology, which is based on stopping photosensitisers in skin from generating any ROS when excited by light.
epidermis and dermis. Between 19%-50% of UVA reaches the basal layer of the epidermis, whereas only 9%-14% of UVB does. The total amount of UVA energy reaching the basal layers of the epidermis is up to 100 times higher than the total amount of UVB energy. This is supported by findings that show that the epidermal basal layers of patients with certain skin cancers harbour more UVA than UVB mutations. UVA can act on chromophores, the functional groups capable of absorbing the
OO OOH N C OMe ET=295 kJ/mol ET=245 kJ/mol OMe O O N C APP-2 N C O ET~262 kJ/mol O O
1.0 0.8 0.6 0.4 0.2 0.0
350 400 450 500 λ (nm)
Phosphorescence spectra in ethanol glass at 77k. Metyl iodide was added to increase the phosphorescence yields for APP-2 (33% Mel), APP-3 (20% Mel) and NMC (20% Mel). App-1 did not show detectable phosphorescence. NMC should quench triplet states of the keto form, but not the enol form of avobenzone.
Figure 1: Triplet state energy levels as measured using phosphorescence spectra at 77K. PERSONAL CARE EUROPE 550 600 650 700 O O
ET=228 kJ/mol APP-3
O O NMC ET=233 kJ/mol
UVA energy, which then undergo photoreactions and cause direct damage at a cellular level. The epidermis contains several known UVR chromophores, such as certain proteins, DNA, trans-urocanic acid, and melanins and their precursors. UVA radiation can also indirectly cause photodamage by generating reactive oxygen species (ROS) and free radicals from photosensitisation. Photosensitisers are molecules that absorb light, become excited, and then
norm. intensity
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