Confession: I don’t use sunscreen and I love a bit of ‘healthy’ colour (read: sun damage). Why the blog series then? Because I am a Fitzpatrick type II of north European ancestry, was diagnosed with eczema/ dermatitis twenty years ago and – perhaps inevitably – with rosacea about six months ago. Given that I live in the notoriously cold/ cloudy/ rainy UK, do I really need to put my big girl pants on and use sunscreen regularly?

Image credit: brnrd.me

Sensitive Skin

UV damage is widely known to be a risk factor for erythematotelangiectatic but not for papulopustular rosacea. However four out of five rosaceans report sunlight to be a trigger for a flush or flare. Many are also affected by linked factors such as warmer weather (three quarters) or higher humidity (just under half). Some rosaceans – myself included – have increased perspiration or higher skin temperature than those without the condition. This can limit sunscreen choice and impact efficacy.

What is less well known is the link between atopic eczema (AD) and sunlight sensitivity. A study published in 2009 concluded that “photosensitivity is found in approximately 3% of patients with AD and the majority are female.” Interestingly some patients reacted to UVA, others to UVB but some were sensitive to both UVA and UVB light.

Subclinical – not visible to the naked eye – photosensitivity may be even more prevalent. In 2010 researchers found that a common (10%+ of Europeans) group of genetic mutations which confer a strong risk factor for AD, hayfever and asthma “allows more UVB to reach viable [keratinocytes] than would normal stratum corneum, thereby inducing higher levels of DNA damage.” Since the work was in mice and in human tissue not eczema patients further research is needed.

SPF & UVA Ratings

UVB penetrates the epidermis (upper layers of skin) where it stimulates synthesis of vitamin D3, is the primary cause of sunburn and a major player in skin cancers. If sunscreen products are applied and reapplied correctly the amount of UVB radiation blocked by SPF 15 is 93%, SPF 30 is 97% and SPF 50 is 98%.

The National Institute for Health and Care Excellence (NICE) advise UK doctors “recommend the frequent application of high-factor sunscreen (minimum sun-protection factor 30) to the face whenever the [rosacean] is going to be exposed to sunlight.” The International Rosacea Foundation advocates an SPF of 45 or over is employed.

However up to 95% of the UV radiation that hits our skin is UVA. This can penetrate cloud and glass all the way to the dermis (lower layers of skin) causing the unseen structural and molecular damage that is implicated in wrinkles and rosacea. So the British Association of Dermatologists goes further than NICE, explaining the need for “both UVA and UVB protection … sometimes called ‘broad spectrum’. A sunscreen with an SPF of 30 and a UVA rating of 4 or 5 stars is generally considered as a good standard of sun protection.”

Image credit: WHO

Some research suggests that – rather than being constant – the true SPF of a product may vary depending on the time of day, season and latitude. This is because both UVB and UVA contribute to erythema (redness: in this case sunburn), because the relative input of UVA and UVB to the total UV radiation exposure varies substantially, and because “the SSR spectrum specified by regulatory bodies for SPF assessment contains more UVB relative to UVA than is found at the equator at noon“!!

So what does this mean for us Brits? A study from 2010 considers how sunscreen performs at temperate latitudes – a ‘band’ encompassing much of Europe, central Asia and a good chunk of the United States – using a UV source with more UVA and less UVB, intended to better mimic the spectrum of radiation we are exposed to. The subjects were exposed to a third of the dose needed to cause erythema every day for a fortnight.

The researchers found that, irrespective of the simulated latitude or simulated time of day, the broad spectrum sunscreen performed as predicted by standard SPF testing. However for the UVB-only sunscreen “the calculated SPF of the UVB sunscreen was 50–60% less than the SPF that would have been determined under the current testing standards.”

The study was very small, only used two Fitzpatrick types and one SPF of 6, so further research is warranted to determine whether this effect is consistent through higher factor products, and how much application rate and frequency (see part 2/2) affect the protection at different latitudes. For the time being it seems prudent to use products that offer good UVA protection.

The UK and Ireland’s star rating for UVA protection is expressed as percentage of UVB protection; it is licensed by Boots and applies to many brands sold in their stores. High street retailers such as Superdrug, Tesco and Wilko also use the star system on their own brand sunscreens. Other parts of the world have different rating methods: in east Asian there is the PA system, the US and Canada use PPD, Australia and New Zealand simply label products that meet a certain standard as ‘broad spectrum’.

Image credit: Uvistat

The UV Index

This “identifies the strength of the ultraviolet (UV) radiation from the sun at a particular place on a particular day, allowing you to take the necessary precautions to help reduce the impact of UV on your health.” The predicted UV index for UK towns and cities is part of the Met Office’s daily weather forecast; our UV index is 0 to 2 for several months from late autumn through early spring and rarely exceeds 7.

Image credit: WHO

The Met Office predict the UV index hour-by-hour; the variability is primarily down to the relative intensity of UVB which is more affected by the changing height of the sun than UVA is. This means that “the UV index is weighted more towards UVB frequencies and tends to underestimate UVA exposure. [It] is more useful in assessing the risk of sunburn than long-term damage to the dermis and skin matrix that leads to wrinkles.”

Still the World Health Organisation (WHO) and Cancer Research UK agree that “even for very sensitive fair-skinned people, the risk of short-term and long-term UV damage below a UVI of 2 is limited, and … no protective measures are needed.” In the UK this is roughly October to March, unless there is snow on the ground which reflects UV and intensifies exposure.

As already noted UV can penetrate cloud and glass. The Australian Bureau of Meteorology explained why cloud does not necessarily affect the UV index or reduce risk. Not only can UV penetrate thin cloud but “patchy clouds can also intensify UV levels because radiation is reflected off the clouds’ edge. In other words you get a mirror effect and the UV can bounce off the clouds and focus on the ground.”

So no ‘get out of jail free’ card for us in the UK then?!

Sunscreen series continues at: The numbers game 2/2