We find ourselves in a socially atypical situation owing to the sudden change in our once normal living patterns. Our relationship with the environment has been affected by the COVID-19 pandemic, especially in terms of spending time outdoors.

Lockdown has created a situation in which most people have had less exposure to sunlight than usual, and this in turn has led to a springtime where degrees of exposure are similar to, or even lower than, those of winter. In terms of exposure, therefore, we might say that we have had a longer winter. This in turn leads us to believe that as the positive effects of naturally progressive exposure to sunlight on the skin have diminished, the natural biological response in the skin has also been altered. Hence, cutaneous synthesis of vitamin D, which is our greatest source of vitamin D, has been hampered by the lockdown, during which many people have not been exposed to sunlight in several weeks. Blood vitamin D levels vary according to the season, with lower values in winter than in summer1; however, during the COVID-19 lockdown, the winter low-exposure period has been extended by more than 3 months. Low vitamin D levels have pathophysiological consequences, and given that vitamin D can reduce the risk of infection through various mechanisms, the possibility that a deficiency could render us more susceptible to infection by coronavirus is somewhat alarming.2 Consequently, various sectors, including health care, have recommended direct—albeit brief—exposure to sunlight in order to increase serum vitamin D levels.3 Similarly, we should not forget the benefits of exposure to sunlight for our state of mind, which is considerably affected by the current situation, through stimulation of the neurotransmitters involved in the mechanisms underlying emotional well-being.

Easing of the lockdown has been planned in phases by government bodies as a gradual, responsible, and considerate “return to normal”. However, as far as our skin is concerned, the risk of direct exposure resulting in sunburn is greater, because the usual change from winter to spring at the latitude of Spain coincides with a gradual change in the incidence of solar radiation, thus enabling an acclimatization that is also gradual. Our pigmentation system is still in the winter period, with melanin levels that are lower than usual for the different skin phototypes. Therefore, the protection provided by progressive melanogenesis is very limited, since it depends directly on the impact of UV radiation on the skin.4 Lockdown has curbed the processes of melanogenesis, hyperkeratosis, and epidermal hyperplasia in response to the gradual acclimatization of the skin to sunlight, thus making the skin more sensitive to more aggressive and energetic solar irradiation (UV).5 In addition, the photoimmune response may be affected by the lack of exposure to sunlight, thus favoring an increase in the incidence of photosensitivity disorders resulting from the absence of a process of vaccination or hardening.6

Solar irradiation values with the potential to cause erythema are expressed as the ultraviolet index (UVI). Normal maximum UVI values in our region at the start of spring are 3-4. In this case, easing of lockdown coincided with a summertime outside temperature and a maximum daily UVI of 9 or 10.7 At such values, persons with low skin phototypes are exposed to the minimal erythema dose in less than 20 minutes and therefore experience sunburn.

Furthermore, heat plays a double-negative role in the skin. On the one hand, during the early months of spring, the moderate temperature means that we are exposed to sunlight while fully clothed (as on cloudy days), whereas, from May onward, the increase in temperatures means that we are exposed to sunlight with less clothing, when the UVI is at yearly maximum values. On the other, this period of the year is characterized by very high temperature peaks that can worsen lesions caused by UV radiation.

Therefore, when people are keen to be outdoors after the long lockdown period, there is clearly an increased risk of sunburn. The skin has had no time to adapt, and this could have long-term repercussions in the form of an increased incidence of skin cancer.

Healthy exposure is achieved by ensuring that the dose of UV radiation is sufficient to achieve the positive effects of sunlight on our body and to minimize the risk of damage resulting from overexposure. UVI values can be used to calculate the minutes of exposure taken to reach the minimal erythema dose. Table 1 shows the minutes of exposure to sunlight at midday in summer and winter, by skin phototype, that would be necessary to develop erythema (sunburn) and to produce a healthy dose of vitamin D.

Furthermore, the duration of exposure necessary to produce erythema and for synthesis of vitamin D differs with the time of day. Thus, this is longer in the morning and the evening because of the daily cycle of sunlight, where maximum radiation is around midday (Table 2). Photoprotective measures are recommended when the incidence of solar UV is high, since the doses of UV necessary to produce vitamin D are low and can be reached with a simple walk and exposure of small areas of the body, such as the face and hands. Table 3 summarizes the recommendations for the general public so that the benefits of the sun can be obtained without health risks.

In conclusion, the COVID-19 lockdown has led to an unprecedented alteration of our physiological mechanisms for adapting to sunlight. Standard photoprotective measures are of particular importance under these circumstances.