Skin is the visible protective cover of our body. Skin breathes – and gives off warning signs. But what is particularly interesting is that our skin evidently registers brightness.
The largest organ
Skin is not only the largest organ of the human body, it also fulfils numerous functions that are vital for the organism. Through its tactile perception, it becomes the visible protective cover of our body. Skin breathes – and gives off warning signs. When we are in the open air, we feel rain, it gets cold. If we are exposed to the blazing sun, we sweat and our skin burns. If we cut our finger while chopping vegetables, the wound stings because the skin transmits stimuli to our brain. But what is particularly interesting is that our skin evidently registers brightness. It distinguishes light and dark without us having to open our eyes – because the skin senses the time of day.
Skin reacts independently
Mammals such as mice carry photoreceptors in the layers of their skin. These receptors are also responsible for the biological circadian rhythm of day and night. The human skin also has pigments that recognise light, as tests with mice have shown. With the help of the skin pigments, known as melanin, it is possible that our inner clock automatically adjusts to the given time of day, independently of ocular vision and the brain. Our skin thus appears to react autonomously. Our metabolism also follows the circadian rhythm – i.e. the cycle of approx. 24 hours – which is synchronised with the environment with the help of special genes and controlled by brightness such as daylight. Light-sensitive pigments, which are also found in the eye, transmit information about the incidence of light to the brain. The brain receives the stimuli, while at the same time regulating the release of hormones and controlling the sleep hormone melatonin.
Of octopuses and chameleons
Skin cells contain light-sensitive molecules that act as clocks for our sense of time. Apparently, we can tell through our skin whether it is daytime – even if a sleep mask covers our eyes. Scientists have found out that a substance called neuropsin (OPN5) is present in skin cells and is thus responsible for the perception of light. Proteins of this group are not only formed in the human eye, but are also found in the skin of octopuses and chameleons, where they are presumably responsible for the change of colour. Opsins even function as shadow detectors in sea snakes. We can state, then, that many mammals have photodetectors for different reasons and for different functions. It is generally known that wound healing processes depend on the time of day. With this background knowledge, it is advisable to have blackouts in the bedroom, especially during short summer nights, as our precious organ – the skin – is just as much influenced by daylight as our eyes.
Source: University of Washington Health Sciences / UW Medicine