Myth: 80 per cent of skin ageing caused by UV rays

From the daily mail to high-quality, reputable journals, the statement ‘UV rays account for 80 per cent of skin ageing’ is plentiful.

First of all, there are many causes of skin ageing such as the natural ageing process, pollution, gravity, diet, smoking, illness and stress. So ‘UV rays cause 80% of skin ageing’ is a pretty bold statement to make. It seems almost absurd that anything could have more of an effect on skin ageing than the inherent ageing process. So let’s explore this claim.

Skin basics

Firstly, let’s explore the structure of our skin.

For a more in depth look at the skin’s structure, see my collagen supplements and retinoid posts.

But, briefly there are a couple of things we should know.

The formation of reactive oxygen species and the induction of matrix metalloproteinases (MMP) reflect the central aspects of skin ageing (whether due to the intrinsic ageing process or extrinsic factors). MMPs are multifunctional enzymes which function in the extracellular environment of cells and degrade both matrix and non-matrix proteins.

Several types of MMP are known to break down elastin and collagen (see collagen supplement post to learn how important these proteins are). Fibroblasts are the cells responsible for the synthesis of elastin and collagen.

We should also know about mast cells. Mast cells play a role in the extracellular matrix remodelling, as well as inflammation and in the formation of new blood vessels. All associated with skin ageing.

The literature for this claim

Quantifying study

A study in the Clinical, Cosmetic And Investigational Dermatology journal aimed to clinically quantify the effect of sun exposure on facial ageing. Participants in the study were either classified as sun-seeking or sun-phobic.

The paper concludes that ‘UV exposure seems to be responsible for 80% of visible facial ageing signs’. Whilst they did find that the sun-seekers appeared older than their real age in several age classes (this peaked at appearing 5 years older), both sun-seekers and the sun-phobic appeared younger than their real age in the 70+ age group.

Their studies show that there is a much greater difference in wrinkle scores between the different age groups than the sun-behaviour groups (i.e. age is a more important factor). So how did they come to propagate the UV exposure causes 80% of skin ageing claim?

The authors calculated a ‘sun damage percentage, SDP’. This supposedly allows us to assess the effect of sun exposure on the face. Does it really though? On average, the parameter is 80.3% ± 4.82%. Does it really mean UV exposure is responsible for 80% of visible facial ageing signs?

They found that with a SDP of 80%, the women have similar apparent age to real age. At 82%, then apparent age becomes higher than real age. Finally, a SDP of 78% means that the woman looks younger.

SDP actually represents the percentage between specific photo-ageing signs and clinical signs i.e. the sun can affect, on average, 80% of the visible clinical signs of ageing such as wrinkles, fine-lines, pigmentation etc. This does not mean that 80% of the clinical signs of ageing are attributable to the sun. It just means the sun can affect these signs, 80% of the time.

Firstly, this study does not look at other factors such as diet (and other lifestyle factors) which have a huge effect on skin ageing. Let’s also not forget that genetics affect the skin ageing process; recent studies on twins have revealed that up to 60% of the skin ageing variation between individuals can be attributed to genetic factors.

Anecdotal evidence

A skin ageing review from the Journal of the European Academy of Dermatology and Venerology cites some research findings which appear to directly compare photo-protected old and young skin: “The dermis of photoprotected aged skin shows fewer mast cells and fibroblasts than photoprotected young skin, and collagen fibres and elastic fibres are rarefied.”

Great, so the research shows that skin ageing is a direct result of ageing rather than the sun. But then the authors contradict themselves saying “Extrinsic skin ageing primarily arises from UV-light exposure. Approximately 80% of facial skin ageing is attributed to UV-exposure.”

For this bit of insight they cite an old research paper from 1997 that suggests “at least anecdotally, that as much as 80 percent of facial ageing is attributable to exposure to the sun”.

Two problems here: the paper is from 1997 and we are basing this claim on anecdotal evidence (from the 1900s).

A review in the journal of pathology looked promising, saying: “there are two primary skin ageing processes, intrinsic and extrinsic. Variations in individual genetic background are thought to govern intrinsic ageing, which results as time passes. By definition, this form of ageing is inevitable and, thus, apparently not subject to manipulation through changes in human behaviour.”

“Conversely, extrinsic ageing is engendered by factors originating externally that are introduced to the human body, such as smoking, excessive alcohol consumption, poor nutrition, and chronic exposure to the sun. Exposure to such elements, which falls within the voluntary realm, although it may sometimes occur under duress, is not inevitable and thus represents premature skin ageing.”

However, they then went on to say: “Of these external factors, sun exposure is considered to be far and away the most significantly deleterious to the skin. Indeed, 80% of facial ageing is believed to be due to chronic sun exposure”. Quoting that same 1997 paper.

It seems that there is a common theme: this claim seems to be based on anecdotal and perhaps outdated evidence. There are many more examples where this 80% claim is plucked from thin air.

Summary

I’ve always suspected that the claim ‘UV rays cause 80% of skin ageing’ is rather inaccurate since a lot of the evidence is anecdotal, misleading or subjective. Often the claim is exaggerated and they’ve marketed it so (so you want to read the article/buy a product). An example of this is the ‘sun damage percentage’ discussed above, it’s a rather misleading concept. In addition, there are plenty of dedicated sunscreen users who look their age. Smells like the natural ageing process to me.

Key takeaways

  • There are likely many factors playing a role in the ageing of your skin: predominantly the natural ageing process, but there is no doubt UV rays, pollution, diet etc play a role too.
  • It is likely UV rays do contribute to the ageing of your skin, although the claim 80% of skin ageing is due to UV rays is very misleading.
  • The following factors all have a role to play in the ageing dermis: (i) intrinsic ageing process; (2) genetics; (3) expression of genes and their regulation; (4) solar radiation; (5) toxicity of the environment (pollution/smoking); (6) diet; (7) growth factors; (8) steroid hormones and (9) mechanical forces. All these factors are additive and interactive, modulating the mechanisms responsible for the ageing of the skin.

References

Kohl, E., Steinbauer, J., Landthaler, M. and Szeimies, R.-M. (2011), Skin ageing. Journal of the European Academy of Dermatology and Venereology, 25: 873-884.

Fields G. B. (2013). Interstitial collagen catabolism. The Journal of biological chemistry288(13), 8785–8793.

Braverman, I. M., & Fonferko, E. (1982). Studies in cutaneous aging: I. The elastic fiber network. The Journal of investigative dermatology78(5), 434–443.

Uitto J. (1997). Understanding premature skin aging. The New England journal of medicine337(20), 1463–1465.

Baumann, L. (2007), Skin ageing and its treatment. J. Pathol., 211: 241-251.

Flament, F., Bazin, R., Laquieze, S., Rubert, V., Simonpietri, E., & Piot, B. (2013). Effect of the sun on visible clinical signs of aging in Caucasian skin. Clinical, cosmetic and investigational dermatology6, 221–232.

Naval, J., Alonso, V., & Herranz, M. A. (2014). Genetic polymorphisms and skin aging: the identification of population genotypic groups holds potential for personalized treatments. Clinical, cosmetic and investigational dermatology7, 207–214.