Sunscreens contain one or more of the following ingredients:
- Organic chemical compounds that absorb ultraviolet light.
The sun protection factor (SPF) of a sunscreen is a laboratory measure of the effectiveness of sunscreen — the higher the SPF, the more protection a sunscreen offers against UV-B (the ultraviolet radiation that causes sunburn).
Some dermatologists recommend the following preventative measures:
- Sunscreens should block both UVA and UVB rays. These are called broad-spectrum sunscreens, which should also be hypoallergenic and noncomedogenic so they do not cause a rash or clog the pores, which can cause acne.
- Sunscreens need to be applied thickly enough to get the full SPF protection.
- Sunscreens should be applied 15 to 30 minutes before exposure, followed by one reapplication 15 to 30 minutes after the sun exposure begins. Further reapplication is necessary only after activities such as swimming, sweating, and rubbing.
- Sun rays are strongest between 10 am and 4 pm. Sun rays are stronger at higher elevations (mountains) and latitudes near the equator.
- Wearing a hat with a brim and anti-UV sunglasses can provide almost 100% protection against ultraviolet radiation's entering the eyes.
- Reflective surfaces like snow and water can greatly increase the amount of UV radiation to which the skin is exposed.
In the EU sunscreen labels can only go up to SPF 50+ (actually indicating a SPF of 60 or higher) while Australia's upper limit is 30+. In the 2007 and 2011 draft rules, the Food and Drug Administration (FDA) proposed a maximum SPF label of 50, to limit unrealistic claims.
Most instructions on sunscreen labels recommend reapplying sunscreen "frequently", but the definition of "frequently" is vague. A common instruction is to reapply sunscreen after 2-4 hours in the sun. However, one study has shown that reapplying sunscreen 15 to 30 minutes after being in the sun is more effective than waiting 2 hours. It is possible that this time period is more effective because most people do not apply enough sunscreen initially, and this second application approximates the actual amount needed. Sunscreen should also be reapplied after swimming, excessive sweating, or toweling.
Applying Sunscreen Properly
Most people use sunscreen improperly by not applying enough. They apply only 25% to 50% of the recommended amount. Sunscreen should be applied liberally enough to all sun-exposed areas that it forms a film when initially applied. It takes 15-30 minutes for sunscreen to be absorbed by the skin, so it should be applied at least a half an hour before going out in the sun. Sunscreen should also be the last product applied especially on the face since some sunscreens can break down in the presence of water contained in water-based foundations and moisturizers.