Sunlight consists of visible and invisible light. Ultraviolet (UV) light is invisible and comprises 5% of the light that reaches the earth's atmosphere. UV rays are classified according to their wave length, measured in nanometers (nm). A nanometer is one billionth of an inch. There are three categories of UV rays:

• UVA (320-400 nm)
• UVA I (340-400 nm)
• UVA II (320-340 nm)
• UVB (290-300 nm)
  
• UVC (200-290 nm)

The majority of the UV light reaching the earth is in the form of UVA rays. UVB rays account for less than 4% of all UV light reaching the earth.UVC rays are usually blocked by the earth's atmosphere and not a concern to humans except at high altitudes or in areas of low atmospheric ozone.

UVB rays are shorter rays than UVA rays and penetrate the superficial skin layer (epidermis) causing the skin to tan or burn. UVB skin damage is readily apparent as sun burn and is a marker for UV over exposure. Most UVB skin damage occurs between the hours of 10 a.m. and 4 p.m. when the sun is at it's peak. As a general rule of thumb remember UVB damage is greater when your shadow is shorter. UVB rays are connected to premature skin aging and melanoma skin cancer.

UVA rays are the main cause of  basal and squamous cell carcinomas and premature skin aging. These rays are longer than UVB rays and penetrate into the middle skin layer, the dermis. UVA skin damage is not readily apparent; you don't get burned. The effects of UVA over exposure may not be noticeable for years.

UVA rays are more subtle than UVB rays as they are strong throughout the day and can penetrate cloud cover and most glass. You can suffer from UVA exposure on  cloudy days; while sitting in your car; or at a window, in the sun. UVA exposure is the most compelling reason to use sunscreen every day. You are often exposed to it when you least suspect it.

To protect yourself from UVA and UVB exposure you need true broad spectrum protection. Broad spectrum denotes protection from both UVA and UVB rays. Many sunscreens claim broad spectrum protection but offer only UVB protection.

In the U.S. there are only nine FDA approved ingredients that offer UVA protection: and of these nine only AVOBENZONE (Parsol 1789), Encamsule and ZINC OXIDE offer total UVA protection.

If your sunscreen does not have one of these ingredients you are not getting true broad spectrum protection and are susceptible to UVA skin damage and UVA caused skin cancer.