Since the early days of human life on the Earth, our skin has been exposed to different levels of light. Recently, due to inevitable consequences of modern life, humans are not exposed to adequate levels of natural light during the day but they are overexposed to relatively high levels of artificial light at night. Skin is a major target of oxidative stress and the link between aging and oxidative stress is well documented. Especially, extrinsic skin aging can be caused by oxidative stress. The widespread use of light emitting diodes (LEDs) and the rapidly increasing use of smartphones, tablets, laptops and desktop computers have led to a significant rise in the exposure of human eyes to short-wavelength visible light. Recent studies show that exposure of human skin cells to light emitted from electronic devices, even for exposures as short as 1 hour, may cause reactive oxygen species (ROS) generation, apoptosis, and necrosis. The biological effects of exposure to short-wavelength visible light in blue region in humans and other living organisms were among our research priorities at the Ionizing and Non-ionizing Radiation Protection Research Center (INIRPRC). Today, there is a growing concern over the safety of the light sources such as LEDs with peak emissions in the blue light range (400-490 nm). Recent studies aimed at investigating the effect of exposure to light emitted from electronic device on human skin cells, shows that even short exposures can increase the generation of reactive oxygen species. However, the biological effects of either long-term or repeated exposures are not fully known, yet. Furthermore, there are reports indicating that frequent exposure to visible light spectrum of the selfie flashes may cause skin damage and accelerated skin ageing. In this paper we have addressed the different aspects of potential effects of exposure to the light emitted from smartphones’ digital screens as well as smartphones’ photoflashes on premature aging of the human skin. Specifically, the effects of blue light on eyes and skin are discussed. Based on current knowledge, it can be suggested that changing the spectral output of LED-based smartphones’ flashes can be introduced as an effective method to reduce the adverse health effects associated with exposure to blue light.

Background: Substantial evidence now indicates that exposure to visible light at night can be linked to a wide spectrum of disorders ranging from obesity to cancer. More specifically, it has been shown that exposure to short wavelengths in the blue region at night is associated with adverse health effects such as sleep problems. Objectives: This study aimed at investigating if exposure to blue light emitted from common smartphones in an environment with dim light at night alters human reaction time. Methods: Visual reaction time (VRT) of 267 male and female university students were recorded using a simple blind computerassisted test. Volunteer university students, who provided their informed consent were randomly divided into two groups of control (N = 126 students) and intervention (N = 141 students). All participants were asked to go to bed at 23:00. Participants in the intervention group were asked to use their smartphones from 23:00 to 24:00 (watching a natural life documentary movie for 60 minutes), while the control group only stayed in bed under low lighting condition, i.e. dim light. Just before starting the experiment and after 60 minutes of smartphone use, reaction time was recorded in both groups. Results: The mean reaction times in the intervention and the control groups before the experiment (23:00) did not show a statistically difference (P = 0.449). The reaction time in the intervention group significantly increased from 412.64 ± 105.60 msec at 23:00 to 441.66 ± 125.78 msec at 24:00 (P = 0.0368) while in the control group, there was no statistically significant difference between the mean reaction times at 23:00 and 24:00. Conclusions: To the best of the authors' knowledge, this is the first study, which showed that exposure to blue-rich visible light emitted from widely used smartphones increases visual reaction time, which would eventually result in a delay in human responses to different hazards. These findings indicate that people, such as night shift or on call workers, who need to react to stresses rapidly should avoid using their smartphones in a dim light at night.