Medicine is becoming increasingly personalised, yet sun protection is still reduced to one standard recommendation for everyone.
French professor of dermatology Thierry Passeron has spent much of his scientific career studying pigment cells. It is precisely this expertise that has made him increasingly sceptical of simple answers about sunlight, skin and protection.
Fast read
- According to Professor Thierry Passeron, sun protection involves far more than SPF alone.
- His research shows that UVA and visible light also contribute to pigmentation disorders such as melasma.
- Different skin types therefore require different forms of protection.
- Skin tone, age, medication and environment can all influence what the skin needs.
- Passeron advocates genuinely personalised photoprotection instead of one universal recommendation for everyone.
I fell in love with a cell
I sometimes say that I fell in love with the melanocyte. That may sound rather dramatic for a scientist, but after decades of research, I still find this single pigment cell endlessly fascinating.
The more closely you study it, the larger the world around it becomes. You begin with pigment and end up exploring light, genetics, blood vessels, fibroblasts, skin ageing and inflammation—as well as the way humans have adapted to their environments throughout evolution.
Perhaps that is what changed the way I think. Early in your career, you search for answers. Later, you discover just how many conditions and qualifications a good answer requires. Nowhere is that clearer to me than in sun protection.
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Our focus on SPF is outdated
My generation of doctors and researchers grew up with a relatively straightforward model. UVB burns and damages the skin. We therefore protect ourselves with sunscreen, and the SPF tells us how well that product protects against UVB. It was simple, understandable and useful communication.
But science moved on. We learned much more about UVA, particularly long-wave UVA, and the role it plays in pigmentation and skin ageing. Later, visible light entered the picture. Yet consumers continued to focus primarily on the one familiar number printed on the packaging: SPF.
I understand why. SPF is simple. UVA is more difficult to explain, and formulating effective UVA protection is technically more challenging. Once visible light, skin type and individual sensitivity are added, the story becomes more complicated still. The skin, however, has no interest in our need for simple messages.
When my patients did everything right
As a dermatologist, I treated women with melasma. I knew UVA was important, so I prescribed good protection against both UVA and UVB. Some of these patients were exceptionally disciplined. They used their sun protection exactly as I had instructed. Yet every spring, the same thing happened: their melasma became darker again.
“We have reduced sun protection to SPF, even though different types of light have different effects—and not every skin responds to them in the same way.”
What were we missing?
As a doctor, you can continue to assume that patients must be doing something wrong. Perhaps they did not apply enough product. Perhaps they spent more time outdoors than they admitted. That is the standard explanation.
But when you observe the same pattern often enough, eventually you have to ask yourself a more difficult question: what am I missing—as a doctor and as a scientist?
Visible light matters too
That question led us to visible light. We discovered that melanocytes contain light-sensitive receptors. One of these is opsin-3. Through this receptor, pigment cells can respond to blue-violet light, activating a signalling pathway that stimulates melanogenesis. The pigmentation triggered by this process may also persist for longer.
The skin can detect light
Biologically speaking, the skin can perceive light. This helped explain what I had been seeing in my patients for years.
You can wear excellent UVA and UVB protection and still receive enough visible light during an outdoor summer lunch to stimulate pigmentation in susceptible skin. Almost immediately, this finding sparked fears about the blue light emitted by phones and computer screens. It is a perfect example of what happens when one scientific finding takes on a life of its own.
Compared with daylight, the intensity emitted by screens is far too low to have the same effect on the skin. Our measurements suggest that it is hundreds of times lower.That, too, is part of science. We must not only demonstrate where an effect exists; we must also say when a popular fear is not justified.
The same sun, different skin
My research keeps bringing me back to the same question: why do we behave as though one ideal form of sun protection exists for everyone?
Before advising someone, you first need to know what you are trying to prevent. Sunburn? Actinic damage? Pigmentation? Melasma? Skin ageing? A photodermatosis? The risk that matters most to that individual should help determine what they need protection against.
SPF 50 alone is not enough
You then need to understand who is sitting in front of you. Fair skin has little natural protection against UVB. Very dark skin has considerably more, but that does not mean it is better protected against every type of light.
When exposed to visible light, more deeply pigmented skin types may actually be more prone to developing persistent hyperpigmentation. The differences in response to UVA follow another pattern again.
Medication can change the advice
Medication matters too. Many photosensitivity reactions are primarily triggered by UVA. Simply telling someone to use a “high SPF” is therefore not enough.
It is not just about visible skin colour
Even visible skin colour tells only part of the story. Pigmentation is an extraordinarily complex genetic process involving hundreds of genes.
Humans have also migrated and populations have mixed over thousands of years. What you see on the outside does not automatically tell you everything about a person’s biological background. This does not mean every sun-protection consultation should involve genetic testing. It does mean we should be cautious about assuming that everyone responds in biologically identical ways.
We want medicine to become increasingly personalised, yet when discussing photoprotection, we still rely surprisingly often on simplified, universal rules.
Science gets sharper, marketing simpler
This has become a growing source of frustration during my career. I have not worked exclusively in academic laboratories and hospitals. For many years, I have also acted as a scientific consultant to the cosmetics industry. There are excellent researchers working within that industry, and it is capable of highly advanced technical innovation.
Problems sometimes arise only when that knowledge has to be translated into a product—and subsequently into a marketing message. The scientist says: biologically, this is something we need to take into account. The response may be: yes, but the market wants something else.
Of course, I understand that. A product has to be usable, comprehensible and commercially viable. You cannot give every consumer a lecture in photobiology before she buys a sunscreen. But there comes a point at which simplification stops being about making knowledge accessible—and starts making that knowledge disappear.
Damage is cumulative
We now know that the skin does not respond to sunlight alone. Air pollution, smoking, diet and sleep also have an impact, and these factors can amplify one another. UVA combined with air pollution, for example, may cause more damage than either factor on its own.
That is what fascinates me—and what makes me impatient. Our understanding of the skin is becoming increasingly dynamic. Science can do more than ever before, yet product development often keeps the application narrow, while communication remains static.
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I want to know who is in front of me
That is why I do not believe the next major development in photoprotection will simply be SPF 100. I expect far more from personalisation.
We already have sensors, smartwatches and apps. Cities monitor air pollution. We can determine a user’s location, the season and a wide range of environmental conditions. We can add information about skin type, medication and age—and perhaps, eventually, genetic background.
Who will develop the app?
Why should we not bring all of this information together? My ideal system would not simply report today’s UV index. It would try to determine what this particular person, in this particular place, with this particular objective, needs. The ideal app has yet to be developed.
Artificial intelligence allows us to combine enormous quantities of information. The irony is that much of the knowledge required already exists. We already know a great deal. We simply make too little use of it in everyday practice.
After all these years, I now look at my own field differently. My first question is no longer: what is the best sun protection?
First, I want to know whom it is for. What are we trying to protect that person against? Under which circumstances? What kind of skin is in front of me? I have learned to ask more questions. To me, that is what progress means. The more we know, the less reason we have to pretend that everyone needs the same thing.
Who is Thierry Passeron?
After completing his medical training, Thierry Passeron specialised in dermatology under Professor Jean-Paul Ortonne at Nice University Hospital. He spent a year working in Dakar before returning to Nice to conduct fundamental research.
From 2005 to 2007, he worked in Vincent J. Hearing’s laboratory at the US National Cancer Institute, part of the National Institutes of Health in Bethesda, where he studied melanocytes and melanoma.
He obtained his PhD in 2008 and has been Professor of Dermatology since 2010. He currently heads the Department of Dermatology at Nice University Hospital and leads a research team within C3M/INSERM. His principal research interests include pigment disorders, melanocytes and melanoma.
Passeron is also the developer of the SunLution skincare range, which I discuss in more detail in this article.
