Anyone paying attention to health warnings has heard about the importance of SPF, but what does it really mean? You might wonder which is better for your skin: sunscreen or sunblock? Get answers to these questions and learn about the potential consequences of sunburns before your next trip to the beach.

What is SPF?

SPF, or Sun Protection Factor, is a measure of how well a sunscreen will protect skin from ultraviolet rays. Also called UV rays, ultraviolet rays emit a form of radiation that causes sunburn, damages skin, and can contribute to the development of skin cancer. Choosing the correct strength of SPF is dependent upon your body’s unique reaction to sun exposure.

For example, if your skin starts to burn after 10 minutes in the sun, applying an SPF 15 sunscreen would allow you to stay in the sun without burning for approximately 150 minutes (a factor of 15 times longer). This is a rough estimate that depends on skin type, the intensity of sunlight, and amount of sunscreen used.

SPF is actually a measure of protection from the amount of UVB exposure and it is not meant to help you determine the duration of exposure. Individual issues, such as light sensitivity or history of skin cancer, will affect your recommended SPF strength. The American Cancer Society recommends using a product that offers “broad spectrum” protection and SPF 30, at a minimum. This means you’re protected against both UVA and UVB rays. What are those? We’re glad you asked.

Ultraviolet A and Ultraviolet B

UVA stands for ultraviolet A and UVB stands for ultraviolet B. Unfortunately, both types of rays can damage the skin, lead to premature aging, and increase the risk of skin cancer. Clothing will not totally protect against either ultraviolet A or ultraviolet B rays.

How UVA Affects You

Too much ultraviolet A radiation from the sun can damage the genetic material (the DNA) in your skin cells. If enough DNA damage builds up over time, it can cause cells to start growing out of control, which can lead to skin cancer.

Difference between UVA and UVB

Ultraviolet B rays have slightly more energy than ultraviolet A rays. They can damage skin cells’ DNA directly and are the main rays that cause sunburns. They are also thought to cause most skin cancers.

The Key to Effective Sun Protection

Avoid sunburns by limiting your sun exposure during peak hours, which are typically between late morning and early afternoon. For maximum protection, consider the following factors:

  • Water resistance. If you’re planning to sweat or go in the water, it’s important to understand how your sunscreen performs when exposed to fluid. Simply because a product is labeled water resistant or waterproof does not mean you’re protected. Typically, you will need to reapply more frequently, such as every 40-60 minutes.
  • Reapplication. Even if you don’t plan to get wet, reapplication of sunscreen is essential to prevent a sunburn. Approximately 1 oz should be enough to cover your body and reapplication is recommended every two hours.
  • Sunblock vs sunscreen. Composed of protective ingredients, sunblock does exactly that; it blocks the sun. But, it is not a standalone solution for sunburn protection. It’s best to use sunblock on very sensitive areas, like your cheekbones or nose, in addition to using sunscreen on your body.

Be Smart & Protect Yourself

Choosing the correct SPF for your skin type and reapplying at regular intervals can prevent sunburn and decrease your risk of skin cancer. Ideally, SPF use should be paired with clothing that offers ultraviolet protection and you should use good judgment regarding the length of time you spend outdoors.