Prof Prue Hart is the head of the Inflammation Research Group at the Telethon Kids Institute in Perth, Australia, which studies the beneficial effects of sun exposure on our health and whether they are the result of vitamin D induced by UV or other molecules produced in our skin during sun exposure.
What exactly happens when the sun hits our skin?
Sunlight is made up of three elements: there is visible light which gives color to everything we see; infrared light, which provides heat; and ultraviolet (UV) light, which is probably the most important for our health.
Too much UV is harmful. The most damaging wavelengths are blocked by ozone in the stratosphere, but UVB and UVA wavelengths pass. The worst effect on our skin is sunburn; this is something we should all avoid because it wreaks havoc on the skin: there is a degradation of normal barrier function and inflammation. It can also affect your skin’s stem cells – self-renewing cells that can differentiate into different types of structural cells in the outermost layer of your skin.
What about sun exposure it does not give you sunburn?
It also has biological effects, and many of them are positive. A molecule called 7-dehydrocholesterol absorbs UVB, which results in the production of vitamin D, which is important for your bones. There are three or four other molecules in the skin that absorb UV rays and initiate pathways that generally have anti-inflammatory effects. They can be complementary or interactive and can be larger at different times of the day and in different seasons depending on UV exposure.
Our skin also contains reserves of nitric oxide, and when the skin is exposed to the sun – especially UVA rays – their release can affect the vascular system, lowering blood pressure. This may help explain why your blood pressure is lower during the summer months compared to the winter months. The release of nitric oxide from the skin during sun exposure can also affect the risk of associated diseases such as type 2 diabetes and metabolic diseases.
How does sun exposure contribute to cancer?
UV rays can also be absorbed by DNA in our skin cells and trigger changes or mutations. This is especially serious if they occur in your stem cells because, while other skin cells grow outward as they grow and eventually break off, the stem cells remain at the base of the skin. If these continue to accumulate changes, it could eventually lead to the development of a cancerous skin cell.
What types of cancer are linked to the sun?
Most skin cancers are non-melanoma skin cancers, which usually do not metastasize or spread. The only one that is potentially really dangerous is melanoma, which can metastasize, and is responsible for the vast majority of skin cancer deaths. Vigilance is therefore essential. Melanoma only accounts for about 1% of all skin cancers, but it is difficult to assess because the number of skin cancers other than melanoma is not recorded in the registers.
The other major types are basal cell carcinoma (BCC), which accounts for about 68% of skin cancers, and squamous cell carcinoma (SCC), which accounts for about 28%. These usually do not metastasize and can be easily burned or cut if detected.
What influences people’s susceptibility to melanoma?
We still don’t fully understand melanoma. Exposure to the sun increases your risk, but it doesn’t necessarily start that way. Genetic susceptibility can be important, but it also appears stochastically. More and more, it is believed that melanin [a pigment that influences the shade of someone’s skin] may not play a major role in protecting stem and progenitor cells at the base of the skin. There are around 17 genes known to strongly influence skin pigmentation, and some of them may contribute to the development of skin cancer.
Can people with black or brown skin develop sun-related skin cancer?
People with heavily pigmented skin have much less melanoma, but they still suffer from them, although they don’t get them in the same places as those with lighter skin – they tend to have them on the soles of the feet. and other places that may not be exposed to much sunlight. But you can’t necessarily diagnose their skin cancer the same way you can in people with fairer skin. So this is a difficult area that requires a lot more research.
Will the climate crisis and / or the thinning of the atmosphere change our exposure to the sun?
The peak of the hole in the ozone layer was to be in the 1990s. Following the ban on chlorofluorocarbons (CFCs), the hole stabilized, but it did not exactly close. This is always a concern because if you have less ozone, you have more UV reaching the surface of the Earth.
Climate change caused by other greenhouse gases could influence cloud cover. If there are less clouds, it could lead to more UV exposure. However, it might also cause people to spend more time indoors, so the relationship isn’t necessarily straightforward.
Door SPF 100 sunscreen exaggerated?
A sun protection factor (SPF) of 50 is sufficient. It will block 98% of UV, while an SPF 100 will block 99%. We need some UV exposure for our health. I use sunscreen if I don’t know how long I’m going to be in the sun, and as a way to avoid sunburn. I also say that you should wear a hat to protect your head and neck as this is where a lot of skin cancers tend to occur.
White Britons living in the Mediterranean often stop using sunscreen once they reach the peak of mahogany … Is it wise?
The skin adapts, but it’s not absolute. A person with lightly pigmented skin never really tans and will definitely be at risk for sunburn if they spend a lot of time in the sun. Recent work by Antony Young at King’s College London suggests that if you have very lightly pigmented skin, you may have a different type of melanin, DNA repair, and antioxidant capacity, compared to a person with very light pigment. darker skin, which could affect the way your skin reacts to UV. These things are influenced by your genetics. Young’s work suggests that tanning offers very limited protection – equivalent to a low SPF sunscreen. It does not necessarily protect against DNA damage or sunburn.
Could we harness some of the immunosuppressive benefits of sunlight to fight conditions such as autoimmune diseases?
Light therapy is a type of radiation therapy that mimics the effects of sun exposure. It has been used for decades to treat inflammatory skin diseases, but our lab investigated whether it could also be used to treat more systemic internal diseases, such as multiple sclerosis (MS) or diabetes. type 1.
In our MS trial, we recruited people with the first clinical signs that they might develop MS, to see if light therapy could stop or delay its development. Half of them received light therapy three times a week for eight weeks, and the other half did not. After one year, we saw a 30% reduction in the number of those who developed MS in the light therapy group. We also detected different profiles of immune blood cells in those who underwent phototherapy, in particular their antibody-producing B cells. And these cells also showed a deadened response when we activated them. We believe this could be important in the development of MS, where immune cells mistakenly attack the brain and nerves.
How to balance the negative effects of skin cancer with its daily benefits?
I think it all comes down to knowing your skin and not getting sunburned, as sunburn is the only type of sun exposure that has been reliably linked to melanoma. All of these other benefits come from suberythemal doses of UV, which means insufficient exposure to cause redness or inflammation of the skin.
The mood element of sun exposure and the outdoors is also very important to our mental health. So I think balance is the key.