​Summary

More than half of people buy or use sunscreens. However, the public seems to be confused about health messages for sunscreen. Although cancer prevention groups promote sun avoidance and regular sunscreen use, 70% of people participating in a beach survey were there to get or maintain a tan, and only half were using sunscreen sunscreen.pdf.

Studies have shown sporadic sunscreen use, from 10% in one study to less than one-third in another. Two-thirds of skiers surveyed in Alberta used sunscreen, while in Australia, three-quarters of adult patients told their family physician they use sunscreen. Only one-third of U.K. parents regularly protect their children from the midday sun, and half their children burn at least once a year.

Some people use sunscreens to prevent sunburns, some to improve tanning, some to avoid wrinkling, some to prolong time in the sun, and some because they believe sunscreen prevents all skin cancers.

Application

Sunscreens work as soon as applied, although some suggest applying sunscreen 30-60 minutes before going outside. The only reason to apply early is to allow absorption so the sunscreen is less likely to be washed off if someone's going in the water.

The average application rate of sunscreens is one-third that used during testing (i.e., an SPF 15 will act like SPF 5 because not enough sunscreen has been applied). The correct amount is enough to make the skin slightly white, transiently until absorbed.

Frequent application is often suggested, but there's evidence that this may not be necessary if enough has been applied the first time. In one study, one application provided the same level of protection as four applications. For some patients, the cost of sunscreen may limit use, if they think repeated applications are required.

Few public health messages tell people how much sunscreen to apply, and most use about 30% of the amount needed to achieve the sun protective factor (SPF) listed on the container. For example, the way SPF 15 is commonly applied, it has an SPF between 3 and 7. Many organizations continue to recommend SPF 15 despite this knowledge.

SPF

There is considerable disparity between the SPF achieved in laboratory tests with artificial light sources and SPF in sunlight. For instance, an SPF 6 sunscreen only had a protective factor of 4.8 in sunlight.

Ultraviolet A wavelengths between the upper end of UVB at 320 nanometers and visible light at 400 nanometers cause sagging skin from photoaging, but UVA is not a major cause of skin cancer. UVB is the major risk factor for developing skin cancer. Parasol 1789 is the best sunscreen blocker of UVA, and most dermatologists recommend broad spectrum sunscreens with Parasol 1789. However, no transparent sunscreen is completely protective, because they let some ultraviolet energy through. Sunscreens that block all UV light are opaque blockers such as titanium dioxide and zinc oxide.

Sunscreens and the Elderly

Few elderly people are likely to develop new skin cancers from present sun exposure, and should be advised to refrain from excessive sun avoidance - which can negatively impact their quality of life - as long as they prevent sunburn. One study showed sunscreen did not alter vitamin D levels in older people, an earlier concern. In fact, some sun exposure is probably recommended for the elderly, since they face a decrease in vitamin D production capacity from aging.

Skin Reactions

Although sunscreen can be both an irritant and an allergen, allergic reactions are rare. Many people put a large amount of sunscreen on the forehead, which flows into their eyes with perspiration, causing a stinging sensation. Advise people to apply a modest amount of sunscreen in this area and wash their hands afterwards, because rubbing fingers covered with sunscreen near the eyes can also cause irritation.

Why Use Sunscreens?

Broad spectrum sunscreens can prevent sunburns, some aspects of photoaging, and actinic keratoses. Some pre-existing actinic keratoses can regress as well. Squamous cell carcinoma may also be prevented, since actinic keratoses are precursors of this condition. Evidence does not suggest that sunscreens directly prevent basal cell carcinoma or melanoma, although intuitively, consistent use from childhood should reduce the risk of these cancers.

Refer to the complete journal article for more information on sunscreen use and effects and recommended areas for future research sunscreen.pdf​.