In choosing a sunscreen, look at the ingredients. Preparations that help block UV radiation are sometimes classified as sunscreens or sunblocks according to the substances they contain. In general, sunscreens contain organic formulas and sunblocks inorganic formulas. However, the term sunblock is used less and less as sunscreens increasingly contain both kinds of ingredients:
Organic formulas contain UV-filtering chemicals such as octocrylene, octyl salicylate, homosalate, and octyl methoxycinnamate (block UVB), avobenzone-Parsol 1789 (blocks UVA), cinoxate, ethylhexyl p-methoxycinnamate (blocks UVB and small amounts of UVA), oxybenzone, benzophenone-3 (blocks UVA/UVB). People should look for a wide-spectrum sunscreen that contains combinations of these ingredients and filter both UVA and UVB. Of note: para-amino benzoic acid (PABA), once a popular ingredient, is now used infrequently. PABA may actually break down in the presence of UV exposure and release harmful oxidants. And many people have an allergic reaction to it. Some products contain PABA derivatives, such as padimate O or octyl dimethyl PABA.
Inorganic formulas contain the UV-blocking pigments zinc oxide or titanium dioxide. Zinc and titanium oxides lie on top of the skin and are not absorbed. They prevent nearly all UVA and UVB rays from reaching the skin. Older sunblocks are white, pasty, and unattractive, but current products use so-called microfine oxides, either zinc (Z-Cote) or titanium. They are transparent and nearly as protective as the older types. Microfine zinc oxide may be more protective and less pasty-colored than microfine titanium oxide.
Inexpensive products work as well as expensive ones with the same ingredients. Unfortunately, there are still no standards for sunscreens, and even those claiming UVA protection may offer very little. In one study, the average UVA protection from a wide range of brands was only 23%. In fact, the average protection on brands not making the claim was 37%!
Organic formulas and inorganic microfine oxides do not protect against visible light, which is a problem for people who have light-sensitive skin conditions, including actinic prurigo, porphyria, and chronic actinic dermatitis. Inorganic sunscreens that protect against visible light and are still cosmetically acceptable are now available in Europe, but not yet in the US.
Calculating the SPF
The sun protection factor (SPF) on all sunscreen labels is a ratio based on the amount of UVB (not UVA) radiation required to turn sunscreen- or sunblock-treated skin red compared to non-treated skin. For instance, people who sunburn in five minutes and who want to stay in the sun for 150 minutes might use an SPF 30. The formula would be: 30 (the SPF number) times five (minutes to burn) = 150 minutes in the sun.
Protection offered by sunscreens may be classified as follows:
- Minimal: SPF 2 to 11
- Moderate: SPF 12 through 29.
- High: 30+. (Although some sunscreens claim SPFs higher than 30, the added protection at such higher levels is insignificant.)
SPF Levels by Age Group
Certain groups should have higher or lower SPFs depending on age and other factors:
- Although sunscreens are safe in most toddlers and children, they should not be the first and only lines of defense. In fact, experts are worrying that by relying too much on sunscreen and not providing other protective measures, parents may actually be increasing their children's risk for melanoma. All young children should be well covered with clothing, sunglasses, and hats as the first line of defense against sunburn. Children should be kept out of the sun during peak sunlight periods. Sunscreens should not be used on babies younger than six months without consulting a physician.
- Older children and adults (even those with darker skin) benefit from using SPFs of 15 and over. Some experts recommend that most people should use SPF 30 on the face and 15 on the body.
- Adults who burn easily instead of tanning and anyone with risk factors for skin cancer should use at least SPF 30.
Timing and Amount of Application
Sunscreen or sunblock should be applied liberally as follows:
- Adults should include sunscreen with a daily skin regimen, even if going outdoors for only a short time.
- Apply a large amount to all exposed areas, including ears and feet. To achieve protection as indicated by the sunscreen's SPF, experts recommend half a teaspoon each for the head, neck, and each arm and a teaspoon each for the chest area, the back, and each leg.
- Apply initially 30 minutes before venturing outdoors for best results. (This allows time for the sunscreen to be absorbed. Then reapply every 15 to 30 minutes while being in the sunlight.
- Also reapply each time after exercise or swimming. (Choose a waterproof or water-resistant formula even if activities don't include swimming. Waterproof formulas last for about 40 minutes in the water, whereas water-resistant formulas last half as long.)
- Insect repellents reduce sunscreen SPFs by up to one-third. Use higher SPFs and very liberal application when applying both.
Possible Hazards of Sunscreens, Sun Avoidance, or Both
When used generously and appropriately, sunscreen products and sun avoidance help reduce the severity of many aging skin disorders, including squamous cell cancers. There are certain concerns, however.
Sunscreen Use May Not Protect Against Basal Cell and Melanoma Cancers and May Even Increase the Risk. Although sunscreens help prevent squamous cell carcinomas and other skin disorders, sunscreens do not appear to provide protection against melanoma and some basal cell cancers. In fact, some studies have reported a higher association with sunscreen use and these skin malignancies, though not all studies report such negative results.
The reasons for this possible increased risk are unclear, though some theories include the following:
- Until recently, many sunscreens blocked only or predominantly UVB rays and not UVA, the more deeply penetrating rays now known to be especially dangerous. Studies then may not have reflected the effects of the broad-spectrum sunscreens now available, which block both UVA and UVB.
- People who apply sunscreens may feel safe and stay out longer during high sun-exposure hours than is safe. Even if a person doesn't sunburn, UVA rays can still penetrate the skin and do harm.
- People may not put on enough sunscreen. In fact, according to a 2002 study, people generally apply only 20% to 60% of the recommended amount, which can provide significantly less protection than the given SPF.(Of note, a 2003 study reported that when applied at the recommended amount, a broad-screen sunscreen prevents DNA damage from UV exposure. However, omitting it even once resulted in significant cell injury.)
Sunscreens Use May Increase the Risk for Health Problems Related to Sunlight Deficiencies. There is some major concern that underexposure to sunlight, due to the use of sunscreens or sun-avoidance measures, may produce other health problems, such as the following:
- Vitamin D Deficiency. Vitamin D is only found in a few foods, such as fortified dairy products and fish, but it is primarily manufactured as a chemical response to ultraviolet B (UVB) sunlight. A medical literature review published in the journal Nutrition and Cancer reported that UVB rays may outshine dietary supplements for building the body's vitamin D reserves. Without an appropriate mix of diet and supplements, vigorous sun protection measures may increase a person's risk for developing vitamin D deficiency. Vitamin D is important for prevention of rickets and osteoporosis and some cancers, including melanoma. People who need to avoid sunlight and whose diet is low in foods that contain vitamin D should check with their physician about taking supplements. People with darker skin are at higher risk for deficiencies from sun protection than those with whiter skin. (Note: vitamin D is toxic in high doses.)
- Other Cancers. Although sunlight is implicated in skin cancers, it is also associated with lower risks for breast, prostate, ovarian, and colon cancers. Some protection against these cancers may be related to vitamin D production by sunlight.
- Depression. Many people suffer from SAD (seasonal affective disorder), a form of depression that generally occurs in winter and is associated with exposure to less sunlight.
The bottom line is that some sunlight is important and even necessary for a healthful and high-quality life. Some experts recommend that adults may benefit from daily moderate tanning (20 to 30 maximum minutes of exposure during lower-risk hours) over a number of days to slowly build up pigment in the skin.