UVA, UVB, and Broad Spectrum

The label broad spectrum has become a popular label in sunscreens in recent years. This label is a statement that the sunscreen protects the user from both UVA and UVB rays.

UVB Rays

UVB, in the range of 290-320nm are short waves of solar rays. The amount of UVB rays that we are exposed to varies depending on the season and the time of the day. During the winter, less UVB rays reach the earth's surface.

Only 5% of the UV light that reaches earth's surface consists of UVB rays as the rest are UVA rays which penetrate the atmosphere easier. SPF is a popular measure for the amount of protection that a sunscreen product provides against UVB light.

Earlier sunscreens focused on UVB light as it was thought to be the most damaging rays. Below are some of the effects that UVB rays can have on the skin:

  • UVB rays penetrate only the surface layer of the skin, but are responsible for causing sunburn-redness, inflammation, and blistering that occur after sunbathing are due to the effects of UVB exposure.
  • UVB rays also stimulate and activate cells called melanocytes which are responsible for producing pigment or color. Tans are evidence of UVB damage, although a natural tan does help to protect the skin from further UV exposure to a small degree.
  • UVB is also known to cause non-melanoma cancers, and pre-cancers like actinic keratosis.
  • UV rays cause direct DNA damage which induces mutations that have the potential to become cancerous. UV radiation which includes both UVB and UVA radiation is considered a class I carcinogen, which means that it is a known cancer-producing agent.
  • In addition to its carcinogenic properties, UVB can suppress the immune system, making you more vulnerable to infection. This immunosuppressive property is sometimes used in medical practice, for example in treating autoimmune skin diseases like psoriasis where controlled suppression of immune response is desired.

UVA Rays

UVA rays are long-wave solar rays ranging from 320-400nm. UVA rays can penetrate through clouds, windows, and light clothing. UVA rays can also penetrate into deeper layers of the skin, and it is thought to be responsible for long-term damage to the skin such as loss of elasticity in the skin, premature wrinkling, and may play a role in causing certain types of skin cancers.

Unlike UVB rays, we receive the same amount of UVA year round. This is why it is critical to use sunscreens on a daily basis, and not just for beaching in the summer.

  • UVA rays are longer, and penetrate deeper into the skin.
  • UVA rays are thought to be responsible for wrinkles and general loss of elasticity in the skin, or leathery textures on the skin surface.
  • Damage from UVA rays accumulate over time, and can manifest quickly around the age of 30.
  • UVA damage was not well understood until recently, and some of the older sunscreens do not protect against UVA. It is important to use a sunscreen that protects you from both UVB and UVA rays.

Broad spectrum

The label broad spectrum has become a popular label in sunscreens in recent years. This label is a statement that the sunscreen protects the user from both UVA and UVB rays. Note that SPF ratings only measure a product's capacity to block UVB light. If a product does not display either "broad spectrum protection" or "protection from UVA light" it is likely that the product only offers protection from UVB light.

You want to ensure that you are being protected from both spectrums of light, as they are both damaging to the skin.