Photoaging is the long-term consequence of sun exposure. While not threatening to life, it does reduce quality of life. Repeated unprotected exposure to UV light leads to premature wrinkling, sagging, a leathery texture and hyperpigmentation (“aging spots”). UV light produces DNA damage that may also lead to mutations in genes involved in the development of skin cancer. Therefore, along with other sun safety strategies, sunscreens that absorb or block UV rays serve an important protective function.
No sunscreen provides 100% protection from all harmful UV rays. Practice safe sun exposure habits: wear hats, long sleeve and long leg garments, and avoid unprotected sun exposure whenever possible. Apply sunscreen liberally on exposed skin and remember that sand, snow, and water intensify exposure because of reflected as well as direct radiation. Clouds are only partial protection and significant UV penetration can occur. Sun exposure is cumulative – your skin remembers forever.
UVA and UVB Radiation – What’s the difference?
It is estimated that 80% or more of skin aging is due to photoaging caused by UVA and UVB radiation from the sun. No other cause of skin aging comes close.
UVB light is able to penetrate the outermost layer (epidermis) of the skin and is considered a direct DNA mutagen that damages elastin and collagen, resulting in superficial wrinkling of the skin. While the epidermis does not contain blood vessels or nerve ending, it is the layer where melanocytes and basal cells are located. When exposed to UVB rays, melanocytes produce melanin, the pigment in abundance in dark skinned people, and the reason lighter skin individuals develop suntans. Freckles and dark spots, two additional signs of photoaging, are also caused by accumulations of melanin. Over time, UVB rays can induce cancer or precancerous lesions.
UVA light penetrates deeper into the skin, making UVA damaging to the both the epidermis and dermis. As the thicker, denser layer comprised of collagen, elastin, and extrafibrillar matrix – the structural support system of the skin – damage to the dermis results in more pronounced wrinkles. Because of the presence of blood vessels in the dermis, UVA exposure can cause dilated or broken blood vessels, most commonly visible on the nose and cheeks. UVA also damages DNA indirectly through the generation of reactive oxygen species (ROS) which includes superoxide anion, peroxide and singlet oxygen. These ROS damage cellular DNA as well as lipids and proteins.
Acute overexposure to the sun results in the inflammation and vasodilatation we recognize as sunburn, caused by a panoply of cellular signals and messengers called cytokines including NF-κB, TNF-α, interleukins 1 and 6, VEGF, and others. But chronic exposure is also damaging, whether or not there are episodes of redness and pain. The prudent precaution is to always use sun protection when outdoors, whether working, relaxing, or engaging in any other activity.
Myth Busting – “It’s good to get a little color”
Not true. A suntan is not a sign of health – it shows that your skin has been damaged. Sun damage is not reversible and usually happens before you can see or feel it.
- A tan protects you from sun damage.
Not true. Overexposure to the sun increases your risk of skin cancer and causes premature wrinkling
- People with dark skin are already protected
Not true. Everyone, regardless of skin type, needs protection from the sun.
- Staying in the shade prevents burning
Not true. Even if it’s cloudy, surfaces such as water, sand, concrete, and snow reflect the sun’s rays on to your skin. Clouds filter about 80 percent of the ultraviolet rays, but UV can penetrate thin clouds, fog and haze.
- You will not sunburn while swimming.
Not true. The sun’s rays penetrate under water. Radiation penetrates deeper into the skin when it is wet. Wear a t-shirt and hat while in the water. Use a water resistant sunscreen and re-apply it frequently and liberally.
- Glass protects you from ultraviolet rays.
Not true. UVA rays can penetrate glass and produce some tanning, both immediate and delayed. This can cause premature aging and skin cancer.
Sunscreen or Sunblock? What’s the Difference?
All sun creams and lotions contain one or both of two types of ingredients to combat UV radiation – physical barriers or chemical absorbants. Barrier types (sunblock) contain microscopic particles that block, diffuse, reflect, and scatter UV light. These products are usually thick, white, and may leave a visible residue on the skin until washed or rinsed off. They are usually well tolerated and recommended for people with sensitive skin.
Chemical absorbents (sunscreens) are molecules that absorb UV light, thereby preventing it from penetrating into the skin. Some may also serve to scatter light as well. Unlike sunblock, sunscreen is often clear and can be applied as a liquid, lotion, or spray. More people are sensitive to this type of sun protection. More and more sun protection products are including a combination of both types of UV protectant.
For years, there have been effective UVB sunscreens but not so for harmful UVA rays. Ingredients such as octylcrylene and benzophenones improved UVA defenses considerably. In 1998, the FDA approved the chemical Avobenzone (Parsol 1789) which is effective against all UVA rays.
The terms sunblock and sunscreen are now nearly interchangeable. Many products contain a combination of chemical and physical protectants and are classified as “Broad-Spectrum” because of their effectiveness against both UVA and UVB rays.
The best sunblocks combine both chemical and physical active ingredients. Dermatologists routinely recommend sunblocks that contain either a physical blocking agent or avobenzone (Parsol®1789) in combination with other chemicals. However, in the USA, combinations of avobenzone and physical sunscreens are not permitted. Avobenzone has been reported to be unstable when contained in formulations with physical sunscreens. Surface coating of pigment has sometimes been shown to increase its stability.
Sunscreens designed for infants and children or those with sensitive skin are often based on titanium dioxide and/or zinc oxide. These minerals are less likely to cause skin irritation than the chemical absorbers.
What is SPF?
The SPF rating system was developed in 1962 to measure the capacity of a sunscreen to block UVB radiation. The current SPF rating system continues to apply to UVB rays only, since they are the rays that cause sunburn. There is no approved Sun Protection Factor rating system for UVA rays.
The FDA and other scientists are working on this since UVA is such a huge factor in skin damage. Although UVA rays do not cause sunburn, they penetrate deeper than UVB radiation and cause bigger problems – skin cancer and wrinkles within the dermis.
How does the SPF system work?
The Sun-protection factor system measures the length of time a sunscreen will protect your skin from reddening / burning from UVB rays, compared to how long your skin would take to redden/ burn without sunscreen protection.
If it takes about 20 minutes without sunscreen for your skin to become reddish and start to burn, theoretically by using a sunscreen with an SPF-15 it should prevent the reddening/ burning of the skin 15 times longer, or about 5 hours.
A valid question is do the higher numbers truly afford that much more protection? That depends.
A major consideration is whether or not enough was put on in the first place. Most people use sun protection too sparingly so the SPF number may not be valid. Slather it on thick to make sure the protection is effective. The second consideration is how often sun protection is reapplied, especially after getting wet.
Remember – the SPF system pertains to exposure to the sunburn causing UVB rays. A higher number does not necessarily imply adequate protection against UVA radiation.
As the numbers below demonstrate, there is very little difference in added protection, as the sun protection factor goes higher. That is not to say, however, that it is not worth it. Even small amounts of repeated exposure can add up to a great deal of sun damage.
SPF 15 means 1/15 of the UVB rays get through to your skin – blocking about 93%.
SPF 30 means 1/30 of the UVB rays get through to your skin – blocking about 97%.
SPF 50 means 1/50 of the UVB rays get through to your skin – blocking about 98%.
FDA Oversight of Sunblocks and Suncreens
- New FDA labeling regulations go into effect this year.
- Products previously labeled “broad spectrum” may or may not protect against UVA. The new rule reserves the “broad spectrum” claim only for products that protect against UVA and UVB.
- The old “SPF” designation will show how well a product protects against UVB rays. Products with the new “broad spectrum” label will have to pass a test showing that they protect against UVA.
- Products can claim to protect against sun-related premature skin aging if it has the broad-spectrum designation.
- Sunscreen labels now will be able to claim that a product protects against skin cancer if it has an SPF rating of 15 or higher. Products with SPF rating under 15 must state they do not protect against skin cancer.
- The highest permitted rating will be “50+” as there is no convincing data that SPF levels higher than 50 are meaningful.
- Claims a product is “water resistant” are permitted; claims of “water proof” are not.
- Water resistant products must specify whether protection is for 40 or 80 minutes after swimming or heavy perspiration.
- Product not water resistant must carry a warning to that effect
- No product may claim protection for more than two hours unless proof is submitted.
A total of 17 active ingredients are approved by the FDA for use in sunscreens and sunblocks in the United States. Among them are:
Avabenzone ( Parsol 1789) – many newer products contain Parsol 1789 and are highly effective and appear less irritating.
Benzophenones (Oxybenzone, Dioxybenzone) have been used in sunscreens for 50 years and are known to cause irritations.
Cinnamates (cinoxate, ethylhexyl p-methoxycinnamate, octocrylene, octyl methoxycinnamate) are a frequently used UVB absorber. They are often found in liquid foundations that have an SPF factor.
Ecamsule (Mexoryl SX) an organic compound that is a broad spectrum UV absorbant. It is exclusive to L’Oréal and its brands.
PABA, (para-aminobenzoic acid) was used primarily in the early 1970s and was the first widely available true sunscreen. PABA is a frequent cause of allergic reactions and not commonly used. Related chemicals are used but promotion of PABA-free sunscreens is common.
Salicylates (ethylhexyl salicylate, homosalate, octyl salicylate) are weak UVB absorbers and they are generally used in combination with other UV filters.
Titanium Dioxide is found in almost every sunscreen. It is a blocker of UV light and has strong absorbing capabilities.
Zinc Oxide absorbs both UVA and UVB rays and can be used in ointments, creams, and lotions to protect against sunburn and other skin damage. It is the broadest spectrum UVA and UVB absorber that is approved for use in sunscreen by the FDA.
Questions & Controversies
Sunscreens are not given a clean bill of health by everyone. Certain critics are concerned that the very same phenomenon of UV absorption used to provide sun protection, ruptures double bonds within the molecule of active ingredients and results in free radical generation. Free radicals, in and of themselves, are recognized as agents of DNA and other cellular constituent damage, and are incriminated in both aging and carcinogenesis.
Another concern relates to purported estrogenic effects of some sunscreen chemicals. Because the compounds are quite soluble in lipids, significant amount may be absorbed through the skin and into the body, allegedly affecting sexual function and development – in adults, in children, and in the developing fetus. This controversy is ongoing and unlikely to be resolved any time soon.
There is no free lunch. Risk / benefit analysis must come into play in making the decision as to whether or not to use sunscreens that contain chemical UV absorbents. If in doubt, the option to opt for particulate barrier type protection is always there.
This is a topic of discussion for another posting.