In this post, our Dermatologist Marta Cantarero, will explain how and why to protect ourselves from solar radiation.
WHAT MUST WE PROTECT OURSELVES FROM?
Firstly, we should be aware that not all solar radiation reaches Earth. The radiations that makes it through the atmosphere are the UVA, UVB, visible light and infrared. If we continue damaging the ozone layer, we will also receive UVC radiation, which is not at all convenient for our skin.
Furthermore, different radiations have different penetration capacities in our skin layers. UVB radiation can only make it to the epidermis, the UVA to the dermis, and visible light along with infrared radiation makes it deeper, to the hipodermis. This will determine the different consequences of each radiation on our skin.
Generally speaking, UVB radiation is the cause of acute solar burns and photocarcinogenesis (skin cancer) on the long term; UVA radiation is the cause of strong oxidant stress in our cells that will mainly result in skin aging, and photocarcinogenesis as well. Infrared radiation is what makes us feel heat and is the cause of heatstroke.
Let's get practical; what happens on a cloudy day? Well, infrared radiation doesn't get through on a cloudy day, but UVB and UVA do. We will therefore be exposed to skin photoaging and possible skin burns even though we cannot feel the heat.
What about glass? UVB radiation cannot penetrate glass, so we won't get burned. UVA and infrared radiation, however, do get through glass, so if we are in front of a window, or driving, we will age and feel hot, but we won't get burned.
An important concept to keep in mind is that of reflected radiation, since solar radiation does not just come from above, but different surfaces may reflect that radiation onto us. And so, radiation is reflected on snow at 85%, on water and sand between 10% and 25%, on grass between 2% and 10%, and 2% on asphalt. So beware, being under the umbrella does not necessarily mean that we are safe.
WHY MUST WE PROTECT OURSELVES AGAINST UVB AND IR?
As we have mentioned, UVB radiation is the cause of short-term solar burns, and long-term photoimmunosuppression which leads to skin cancer (actinic keratosis lesions, basal cell carcinoma, squamous-cell carcinoma, and the much-feared malignant melanoma); they all have different destructive capacities on the adjacent tissue, and different metastatic capacity.
WHY MUST WE PROTECT OURSELVES AGAINST UVA?
UVA radiation is the main cause of rapid skin pigmentation, skin photoaging and photocarcinogenesis. Skin photoaging can be recognized by skin loss, thicker skin, lack of luminosity, deep creases and liver spots (“sun spots”).
HOW CAN WE PROTECT OURSELVES?
Our body has naturally developed ways to protect ourselves, such as hair (which is a protective factor mostly in males, since balding becomes a risk factor independently from skin carcinoma on that part of the scalp), sweat (it has a SPF 4 protection factor), and the tan itself.
Depending on our skin pigmentation we can differentiate colors or phototypes from the fairest (phototype I) to the darkest (phototype VI), in which the risk of skin cancer decreases proportionally. Spaniards are generally phototype III, which means we tan after a couple of visits to the beach.
Exogenously, we can protect ourselves from radiation by avoiding peak sunshine hours (12h-16h), using caps and hats, sunglasses, stay under the shade (beware of reflected radiation), using solar-protection clothes (particularly recommended for children) and sunscreen.
There are topical sunscreens which aim to protect the skin's structure and function against actinic damage from the sun.
They were initially created exclusively against UVB radiation. The SFP (solar protection factor) we see when buying sunscreen only indicates the protection degree against UVB (not UVA). Besides, it is important to note that the amount we apply to our skin must be moderate and not scarce, since protection would not be optimal, and it must be applied every 2-3 hours of exposure. Studies show that we usually apply only 20% of the necessary amount when exposed to the sun, and we do not reapply it, so even if we are using a SPF 50 sunscreen, the effect will actually be as if the sunscreen was only SPF 10.
It is important to be aware that there isn't a direct relation between the SPF and the protection against radiation. A SPF 30 sunscreen does not protect twice as much as a SPF 15, since the relation is exponential. A SPF 15 sunscreen protects against 93.3% of radiation, a SPF 20 protects against a 95%, a SPF 30 against a 96.7%, and a SPF 50 sunscreen protects against 98% of the radiation. Therefore, solar protection from SPF 30 onwards is considered “high”.
If we want our sunscreen to protect us against UVA radiation too, we must check on the container that it does, and if the word UVA is circled, it means it protects at least 1/3 of the protection against UVB, which is considered HIGH.
Physical sunscreen, known as “total sunblock”, form an actual layer between radiation and our skin, which reflect all radiation and does not let it penetrate. They are not so well-accepted cosmetically since they tend to be “viscous”.
Chemical sunscreen is more widely used and contains chemical or organic filters that, once soaked into our skin, will absorb different solar radiation wave lengths, protecting us. They become effective after 30 mins, which is why it is very important to apply this type of sunscreen 30 mins before solar exposure.
Regarding biologic sunscreen, it consists of active ingredients that enhance our natural tanning mechanisms, our skin antioxidant system which also enhances DNA mechanisms, and enhancing the skin immune system. It is worth pointing out the existence of polipodium leucotomus, one of the most powerful antioxidants and immunoprotectors, which is currently commercialized.
WHICH SUNSCREEN SHOULD I BUY?
It will depend on the person's skin phototype: if you are a phototype II (fair skin that does not tan) we should use SPF 50. If you are dark-skinned, have dark eyes and don't get burned, we could use SPF 20-30 sunscreen.
Each sunscreen is different and there are currently a wide array of sunscreens special for each skin type and needs: gel or cream texture, antiaging, oil-free, etc.
Children require a special section, since their skin has special characteristics: their corneal layers are thinner, their immune system is less developed, their melanogenesis is not very active, and they have a lower defense against free radicals produced by the sun.
Proper use of sunscreen during the first 18 months, reduces the chances of skin cancer by 78%.
Before age 21, we receive between 50-80% of radiation.
Burns in children under 8 years old: 1/1000 probability of melanoma; several burns in children under 8 years old: 1/100 probability.
Avoid peak hour exposure: 12-16h
Reapply protection every 2 hours and after every swim
Wear a cap and sunglasses
Do not forget that we can get burned during outdoor activities
Sand, water and snow reflect radiation and may cause burns even in the shade.
Pay special attention to children.
Are you protecting yourself effectively?
Dr. Marta Cantarero
Dermatologist at Clínica Áureo and Inca Regional Hospital