Studies have shown that regular use of sunscreens and sun protection beginning in childhood can reduce the risk of developing skin cancer by as much as 75%. Below we discuss what is known about how the Sun’s rays adversely affect the skin. (You can also read “More about the Sun, if you’re interested” at the bottom of this page.*)
The spectrum of ultraviolet radiation has been split into three bands: UVA, UVB and UVC. UVC is blocked by the atmosphere, and is of no concern here. Of the ultraviolet radiation that makes it to the surface, and to us, UVA composes 96.5% and UVB the other 3.5%. Even with what might sound like a small amount, it is UVB radiation that causes sunburn. Both UVA and UVB can cause DNA damage and immunosuppression.
Long term effects of exposure of the skin to UV radiation include:
We have the opportunity to control the amount of ultraviolet radiation that affects our skin, thereby reducing the chance of incurring skin cancer and other unwanted skin changes. The ways we can control our UV exposure can be categorized as the ABC’s:
- Avoid the sun during the mid-day, between 10 AM and 3 PM*
- Block the sun from being absorbed by the skin through use of a sunblock of SPF of 30 or more**
- Cover your skin with clothing: a hat, UV rated sunglasses, long sleeved shirts and long pants to act as barriers
Different sunscreens protect in different ways. Specifically, products containing titanium dioxide protect over the entire UVA/UVB spectrum; zinc oxide protects over almost the same range. Both work by reflecting and scattering UV rays rather than by absorption. (Newer preparations of these oxides in micronized formulations do not have the tell-tale white cast, and are not absorbed into the skin.) On the other hand, chemical sunscreens work by absorbing radiation, and each type protects against specific spectral ranges.***
- As much as 90 percent of the visible changes commonly attributed to aging are caused by the sun.
- About 25% of the long term effects of sun exposure occur during childhood.
- One or more blistering sunburns in childhood or adolescence more than doubles a person’s chances of developing melanoma later in life.
- For people of all ages, a strong association has been noted between cumulative (10 year) sun exposure and the development of actinic keratoses and squamous cell cancers.
People usually apply only about ¼ the amount of sunscreen that is recommended. If you apply SPF 30 sunscreen at only ¼ the recommended amount, the SPF you’re getting is only 3. Proper application requires about 2 tablespoons (an ounce, or about a shot glass full) of sunscreen to the exposed areas of the body to yield 2 mg/cm² of sunscreen. For sprays, continue spraying until you get an even sheen. In addition, if you spray the sunscreen on you will get separate droplets and will not wet all of the skin. You must “rub in” the spray droplets to get them to coat evenly.
UV rays are able to penetrate water to a depth of about 30 inches.
Use dietary supplements to get your Vitamin D; it’s better than getting it from the Sun.
Glass (e.g., a window) blocks UVB radiation, but not UVA, unless specifically formulated or coated to do so.
Clouds and fog reduce infrared radiation a lot; when you don’t feel hot, you might think you’re much less likely to burn. In fact, clouds only reduce UV radiation 30%.
- Overexposure to sunlight can cause cataracts and macular degeneration, a major cause of blindness. Sunglasses can provide effective sun protection for your eyes. However, not all sunglasses are of value. A darker lens itself does not guarantee protection, so look at the label to ensure that the glasses provide UV protection.
Clothing has its own “SPF” called UPF (UVA Protection Factor). Depending on its thickness, type of fiber, weave, stretch, color, etc., clothing might have a UPF of 100 or it might only be 2.
- Wet clothing often conducts UV radiation directly to the skin, reducing the blocking power of the clothing. Change out of wet T shirts.
- Stay out of the sun during the middle of the day. If your shadow is shorter than you are, seek shade.
- Stay in shaded areas whenever possible. “Sun safe” environments should be chosen for outdoor recreation.
- Wear protective clothing, including sunglasses. Wearing UV blocking glasses may be important mid-day even when it’s cloudy because the pupils open more.
- Use extra caution near water, snow and sand: they reflect the damaging rays of the sun, increasing your sun exposure.
- Stay away from tanning beds.
- Use zinc and/or titanium oxides for non-absorbing, broad spectrum sunscreens.
- Chemical sunscreens (other than zinc or titanium oxides) should be applied 30 minutes prior to sun exposure to work properly.
- Sunscreen needs to be reapplied every two hours, or more frequently after swimming, heavy perspiration, or toweling off.
- Wear an SPF rated lip balm to protect your lips from skin cancer. Because it washes off quickly, reapply it often.
- Choose sun protective clothing, try a wide brimmed hat and other clothing with good sun protective ratings.
- Sunscreens are not waterproof. “Water resistant” sunscreens maintain their rating for 40 minutes of immersion in water. “Very water-resistant” (previously called “waterproof”) lasts 80 minutes.
- Use of sunscreens is generally recommended for children older than 6 months of age. It is best for infants to avoid direct sun exposure altogether.
- When applying sunscreen, pay special attention to sun exposed areas. Areas often missed are the top of ears, back of the neck, top of hands and feet and back of the knees.
- Wear sunscreen every day, even in winter.
*More about the Sun, if you’re interested: In cooling itself off from the huge thermonuclear reactions within, the Sun radiates energy, doing so across a large part of the electromagnetic spectrum. Much of the radiation spectrum never reaches the Earth’s surface, because so much is blocked by the atmosphere. Visible light is that part of the spectrum by which we see, and that is, of course, part of the radiation that makes it through the atmosphere. We can feel on our skin another part of the spectrum that makes it through: the infrared radiation that warms us. But there is still more invisible radiation that gets through and is of concern to dermatology. Ultraviolet radiation, the part of the spectrum with a frequency just higher than the violet end of the visible spectrum, does damage to our skin.
The more air between us and the Sun, the more protection we get. So those who live at higher altitudes can receive more radiation than those with more air between us and space. Also, when the Sun is higher in the sky, say between 10 AM and 3 PM, the Sun’s light comes more directly through to us, affecting us more than when it is low in the sky and there is much more air to pass through before the radiation hits us. That’s why we feel hotter under the noon sun than near dawn or dusk.
**SPF: Sun Protection Factor. This designation refers to the amount of protection from UVB radiation a particular product provides. An SPF of 2 means you would have to be in the sun for 2 hours to get the equivalent of 1 hour’s UVB exposure. Wearing an SPF 30 product means you would get 30 times less UVB exposure than not wearing any. [The table below shows how much UVB is blocked for various popular SPF product ratings.] An analogous rating system for UVA radiation is now coming to marketed products: PFA (Protection Factor UVA). Because products marketed as having “UVA Protection” were ambiguous as to whether they provided UVA and/or UVB protection, the US FDA has provided the PFA as a uniform measurement method. The PFA rating is analogous to SPF: a PFA 4 gives twice the protection from UVA as does a product with a PFA rating of 2.
|SPF Rating||% of UVB that is blocked|
***Sunscreen agents and spectrum coverage:
|Cinnamates – octyl methoxycinnamate||X|
|Phenylbenzimidazole sulfonic acid||X|
|Salicylates – octyl salicylate, homosalate||X|
|Dibenzoylmethanes – avobenzone / Parsol 1789,
|Benzophenones – oxybenzone, Eusolex 4360,
methanone, Uvinal M40, diphenylketone