I understand this is a somewhat contentious issue, especially on social media. We already know that countries differ in their advice on sunscreen use; the USA advises sunscreen use throughout the year whereas the UK, EU and Australia advise on sunscreen use if the UV index is 3 or more, or if you work outside, are near reflective surfaces eg snow or are outside for extended periods of time.
Many dermatologists on social media advocate the use of sunscreen daily as part of the morning skin routine ie after cleansing and applying moisturiser, though we also know that for a sunscreen to be effective as part of a skin cancer prevention and anti-ageing routine, it should also be applied regularly throughout the day as it wears off. The current recommendations are of 2-hourly applications with one teaspoon per limb, one for the front of the body, one for the back and one for the head, with a full body application for an adult being about 7 teaspoons (35ml).
There are currently no guidelines in place recommending the use of sunscreen whilst indoors though it is also advocated by many who are prominent on social media. The arguments for this being that most people spend their time indoors and outdoors and also that there are windows which let in light so there will be inevitable UV and visible light exposure from them.
It was very interesting to read, therefore, a Perspective by Brian Diffey from the Translational and Clinical Research Unit of Newcastle University in the August edition of the British Journal of Dermatology.
[Diffey B. Is it necessary to wear sunscreen indoors? Br J Dermatol https://doi.org/10.1111/bjd.21850]
What does he say?
He argues that sunscreen use indoors is not necessary and I must admit, I agree. I only recommend indoor sunscreen use for those that have photosensitive skin conditions such as lupus erythematosus, a porphyria, photosensitive eczema, solar urticaria or xeroderma pigmentosum. Patients with these conditions also are eligible for prescribed sunscreens on the NHS.
What is there to support his argument?
He quite sensibly states that the light levels indoors in places such as offices, showrooms and laboratories are about 20 times less than that compared with outdoor levels on a clear day. Obviously there are variables such as the season, the weather, the dimensions of the room, the orientation and size of windows, reflectance from surfaces, the presence of nearby buildings or trees and scattered sky radiation. However if the outdoor light level from direct sunlight is around 100,000 lux on a clear day and that scattered from the sky is around 10,000 lux, light levels inside by a window may be around 1000 lux and in the middle area of a room, it may be only 25-50 lux.
Many argue that they work indoors by a window and so need to wear sunscreen.
He tackles this too. His main argument being that yes, the UVA irradiance of sun shining directly on an unobstructed window may well be the same as that on a similar vertical surface outside but he argues that this is an unrealistic situation. The glare will be so strong that anyone sitting that close to such a window will either move away or employ measures such as drawing blinds or putting up an awning to reduce the glare.
He points out that there is a factor called Daylight Factor (DF) which is a tool employed by architects and lighting engineers to express the level of daylight in a room. It is a percentage of daylight available inside a room compared to unobstructed daylight outside.
Studies have shown that in an office environment, the most satisfactory Daylight Factor is between 2 to 5%. Anything over 5% becomes uncomfortable and causes an individual to employ measures to reduce the glare ie walk away or draw the blinds.
So should I not wear sunscreen indoors?
At the end of the day, it is down to personal preference and beliefs and your budget. From a skin cancer prevention point of view, indoor sunscreen is not required. From an anti-ageing point of view if cost is a factor, it may be more cost effective to not sit by a bright sunny window or put up blinds or an awning.
From an environmental point of view, the debate is still active as to whether UV filters from sunscreens are affecting marine life (though places such as Hawaii have banned the use of sunscreens containing oxybenzone and octinoxate). Even more pertinent is the fact that many sunscreens come in single use plastic bottles many of which are 50ml in size. Indoor use of sunscreen throughout the year would greatly increase the amount of plastic waste generated.
Dr Sandy Flann, Consultant Dermatologist