Sunscreens are lotions and ointments that block radiation from the sun that can burn the skin and cause even longer-term harm. Recent reviews on the use of sunscreens reveals important tips on how to use them.
Background on radiation, energy, and the Sun
First, some interesting facts about the radiation that we are trying to avoid. When we talk about exposure to strong sunlight, we don’t often use the term radiation. Most of us think about sunlight as mainly consisting of light that we see, and not radiation.
But did you know, that the light that you read by is indeed radiation? It is a type of radiation called electromagnetic radiation. All forms of electromagnetic radiation are physically very similar, but vary in the amount of energy they radiate. We are highly adapted to manage the energy that visible light emits, and so there is very little harm for us to be in plain old light of normal intensity. As a result, we don’t experience light as transmitting or radiating energy, but it does, but the energy we receive from it causes no harm.
But other types of electromagnetic radiation can have either deliver far more intense energy or milder energy that interacts badly with us. The milder energy form or electromagnetic radiation that can cause harm at high levels is microwave, which is lower energy than light, but just the right energy to make water vibrate causing it to heat up (that’s how your microwave works). Even lower energy forms seem very harmless, such as radio waves.
But higher levels of electromagnetic radiation are known to deliver too much energy to our cells, causing damage. Two examples of such energy are ultraviolet, which is just a notch higher than visible light in energy, and X-rays, one of the highest energy forms of electromagnetic energy.
Our sun emits massive quantities of electromagnetic radiation as a result of the massive nuclear fusion explosions constantly underway in its interior.
The electromagnetic radiation emitted by the sun covers the full range of the energies noted above, and so our planet is bathed in a steady wash of radio waves, microwaves, visible light, ultraviolet, and X-rays. Much of the higher energy forms, such as ultraviolet, and essentially all of the highest energy forms, such as the X-rays, are shielded from our bodies by the magnetic belts surrounding earth and the air we are bathed in.
But much visible light, and some ultraviolet radiation gets through to us.
Background on the Ultraviolet
All sunburns and the sunlight contributions to skin cancer are thought to be from the effects of ultraviolet light (UV), as noted above, a form of electromagnetic radiation that is just like regular visible light, but with more energy. UV comes in three levels of energy, UVA, UVB, and UVC. The sun makes all three.
UVA is the least energetic, UVB more so, and UVC very energetic. No UVC gets through our atmosphere to our skin, not much UVB does, and UVA gets through the best.
The lower energy UVA gets to us very readily, and about 90% of UV hitting us on a summer day around Noon is UVA. UVB is higher energy but is blocked by clouds, but on a partly cloudy day, UVB gets through the blue sky sections between the clouds.
UV helps and harms us
Vitamin D is produced when the skin absorbs UV, interestingly only UVB. So some UV is helpful, even the higher energy UVB.
Vitamin A is actually destroyed by both UVA and UVB.
UV damages the DNA in skin cells. In fact, it turns out the familiar sunburn is actually caused by damage to the DNA inside our skin cells. This story is very interesting. The molecule DNA actually does a great job batting away UV radiation, over 99% is kept from being absorbed. But even with 1% or less getting through, a good dose of UV radiation will damage the DNA (only the DNA in the skin cells!). The body gets very upset when it notices a cell’s DNA is messed up, and two things happen quickly. The cell itself notices something is very wrong, and will actually self-destruct. If it fails to do this, then the immune system will take care of making that happen. Either way, a layer of cells with damaged DNA from UV will die and shed. The attack on the cells causes the redness and pain of sunburn, and the peel is from them shedding.
Imagine that, sunburns are the visible manifestation of radiation (UV) damage to our DNA (skin only)!
UV exposure, both A and B, are implicated in the risk of melanoma. The actual amount of that risk is hard to measure and is not known precisely at this time. But UV radiation clearly plays some role in melanoma.
UV exposure, both A&B is a known, common, and main cause of non-melanoma skin cancers, such as basal cell carcinoma, as well as aging the skin.
What does sunscreen do?
The purpose of DNA is very simple: to keep UV radiation from damaging your skin cells. That’s it.
How does sunscreen do it?
There are two types of sunscreens:
- Physical blockade. The most effective blockade is to be in a building with no sunlight. Effective, but not very nice. Another highly effective physical blockade is clothing. And then there are the “paints.” Opaque pigments, typically white, block all light and UV from the skin. These include zinc oxide and titanium oxide, the famous white ointments on lifeguard noses.
- Chemical blockade. These are the familiar sunscreens, containing a chemical that absorbs UV radiation. One other chemical that is perhaps the best at it is made by us, melanin- the source of year round pigmentation of varying intensity by ethnic group, and the source of seasonal tanning in those lacking year round melanin.
How best to achieve the goal of sunscreen use- protection from UV radiation
The only way sunscreen can work is if it is actually on the patch of skin being exposed to sunlight at the time of the exposure and to make sure it contains enough blocking chemicals to keep a burn from happening.
How to be sure there is enough chemical to keep the UV from burning?
This is what the SPF rating does, over a certain number and you can be confident that UV radiation is plenty blocked.
The number itself does not indicate any number of hours of efficacy, it is calculated via complex ratios of UV penetrance with and without use of that sunscreen.
It turns out that an SPF of 30 is more than plenty. SPF of 15 is fine too, but any SPF over 30 fails to offer any benefit beyond what you get at 30.
And this point is very important, all the SPF rated sunscreens fail to keep 100% of UV radiation out of your skin cells. Even lathered up with SPF of 200 (if it exists) will not keep all UV from getting past it.
How to pick the right sunscreen?
- Pick SPF 15 or 30, both work very well, and very close to equally well, more does not help much.
- Pick one called broad spectrum- only these will block both UV A and UV B.
- Pick a brand tested by Consumer Reports (July 2016) and found to have the SPF advertised on its labels: No-Ad Sport, Pure Sun Defense, Banana Boat SunComfort, Coppertone Water Babies, and other labels are listed as delivering the stated SPF (nearly half tested did not!)
How to make sure the sunscreen is applied properly?
Sunscreen will not work if it doesn’t cover the exposed skin or washes off.
To avoid these pitfalls, follow these guidelines:
- For a grade school aged child, apply 2 ounces to cover the exposed body at each application. 2 ounces equals: 4 tbsp, 12 tsp, one shot glass
- Even if advertised as water resistant, it should be applied every 2 hours
That’s a lot of sunscreen, other options:
Yes, back to the physical blockades:
- Swim shirt, swim pants, hat
- Sit in shade when not swimming
- The sun radiates a massive amount of radiation into space. Almost all of that radiation that hits Earth never gets past our magnetic fields and atmosphere.
- The radiation that does is almost all in the form of harmless visible light, and ultraviolet (UV) radiation. Its the UV that causes sunburn, skin aging, and a large number of milder skin cancers, and some proportion of melanomas.
- The ultimate goal is very simple- avoid getting a sunburn, minimize exposure to UV radiation to the exposed skin.
- Being indoors will of course be the most complete solution, but not a good one if you want to play outside or swim.
- When outdoors, particularly from 10AM-4PM- protect skin. Wearing a hat and/or clothing to cover skin works very, very well.
- For skin still exposed, use sunscreens to block the UV radiation. Key items to make sure the use is effective include:
- Use the right SPF- 15 or 30 is plenty. Higher SPF’s are fine to use, but offer little extra benefit
- Use the right amount- about 2 ounces for a grade schooler’s body
- Use the right timing- re-apply every 2 hours during sun exposure
- Use the right brand- check the July 2016 Consumer Reports, about half of sunscreens sold do not have the chemicals the label claims they do. See above for a partial list of those that do have enough per CR
- Use broad spectrum sunscreens, if not labelled with this distinction, it will not protect against both UV A and UV B
We would like to thank and acknowledge Dr. Edward A. Bell for much of the above data as reported in Infectious Diseases in Children, July 2016.
To your health,
Dr. Arthur Lavin