Oxybenzone

Many sunscreens contain the material oxybenzone. This substance absorbs ultraviolet (UV) radiation by forming a barrier on the skin's surface. Energy from sunlight (primarily UVA and UVB) is absorbed, reflected or scattered by materials in sunscreens.

Most people benefit from sunscreens with sun protection factor (SPF) numbers of 15 or more (also called a Sunblock). The SPF number gives you some idea of how long you can stay in the sun without burning. For example, if you burn in 10 minutes without sunscreen and you apply a liberal dose with a SPF number of 15, you should be protected from sunburn for 150 minutes. Sunscreens with SPF numbers higher than 15 may work better for people who are fair-skinned, live at high altitudes, work or play outdoors much of the day, or perspire heavily. Swimming and perspiration reduce the actual SPF value of many sunscreens - even those that are water-resistant - so you have to reapply the product often.

Although sunscreens with identical SPF numbers give you equivalent sunburn protection from UVB rays, no sunscreen product screens out all UVA rays. Some may advertise UVA protection, but there is no system to rate UVA protection yet.

When reading a bottle containing a material that protects you from UV Rays, here are some definitions that might help you in making a decision about which material to use while spending time in the sun.

Sun Protection Factor (SPF)

The SPF is a ratio between the ultraviolet dose required to produce minimal erythema reaction (redness) in protected skin (skin with sunscreen) compared to unprotectedskin (skin without any sunscreen). The SPF number indicates how many timeslonger a person can stay in the sun before beginning to burn while wearing sun protection than if he or she were not wearing sunscreen at all. This amount of time varies from one individual to another.

Sunscreens

All sun-protection products labeled with an SPF of 2 or higher are considered sunscreens. Sunscreen agents absorb, reflect or scatter UV light. Most lotions and oils work by forming a surface layer of sunscreen ingredients on the skin, which absorb the sun's UV rays before they can penetrate the skin.

Sunblock

Sunblock is a term generally used to refer to products in the higher-SPF (15+) categories of protection. No product is a total sunblock, since a percentage of UV gets through.

Ultraviolet Radiation: UVA, UVB, UVC

Ultraviolet (UV) radiation is part of the sun's spectrum - wavelengths shorter than visible light. Ultraviolet rays are divided into UVA 320-400 nanometers), UVB (290-320 nm) and UVC (<290 nm). The UVA spectrum is further divided into UVA II (320-340nm) and UVA I (340-400nm).

UVB rays are the primary cause of sunburning, premature aging of the skin and development of skin cancer. UVA rays are more constant year-round and penetrate deeper into the skin's layers; UVA rays are also harmful and contribute to burning, premature aging of the skin, and the development of certain forms of skin cancer. UVC rays are blocked by the ozone layer and do not reach the earth's surface.
Tanning beds primarily emit UVA rays. This kind of exposure does not show immediate signs of damage, but over time, breaks down the skin's collagen and elastic and thereby can accelerate wrinkles, leathery skin and skin cancers.