When summer arrives, we start to get messages around sun safety and the harmful effects of sun damage, such as the risk of skin cancer. Sun safety is more than just applying sun block. It’s important to understand how the sun’s energy affects our skin and what SPF means in order to properly protect our skin.

Ultraviolet radiation

The sun, our local star, is a giant mass of hydrogen atoms constantly undergoing nuclear fusion that releases massive amounts of energy.

This energy is released in a wavelength spectrum. The longer the wavelength, the lower the energy. The shorter the wavelength, the higher the energy. The visible light that we see is in the middle of this spectrum.

Ultraviolet (UV) radiation is a form of solar energy that is a shorter wavelength than visible light, but can be absorbed by components of the skin. Even though UV represents a small portion of the sun’s energy, it is the main cause of sun damage and skin cancer.

Types of UV rays

When we talk about sun safety, we are really speaking to protecting our skin from the UV energy that is produced by the sun.There are three types of UV radiation. They differ in their wavelength and biological impact on our skin.

UVA radiation: has a relatively long wavelength. It can penetrate into the deeper layers of the skin and is responsible for skin aging and wrinkles.

UVB radiation: has a medium wavelength and can’t penetrate beyond the superficial layers of the skin. It is responsible for delayed tanning, burning and the main culprit for skin cancers.

UVC radiation: has a short wavelength and is the most damaging source of UV radiation. Fortunately, it’s filtered by the earth’s ozone layer and does not reach us.

What does SPF mean?

SPF stands for sun protective factor. An SPF topical or spray is intended to protect our skin from UV rays produced by the sun. The first step to using SPF is ensuring it’s a broad spectrum SPF product, which protects you from both UVA and UVB rays.

Second, it’s important to understand what SPF means for your skin.

How SPF numbers work

SPF UV absorbed by lotion UV that reaches your skin
15 93% 7%
30 97% 3%
60 98% 1.7%


It’s a common conception that the SPF number on the bottle communicates “how long you can be in the sun without burning.” This misconception can become dangerous with higher SPF sunscreens as some users may think they don’t need to apply lotion as often.

From this chart you can see that SPF 30 blocks about double the UV than SPF 15, and that SPF 60 blocks roughly double the UV than SPF 30. Although the SPF 60 blocks out twice as much UV as SPF 30, the actual difference is only 1.3% UV. Although, there is a role for SPF 60 for those with very fair skin types, the majority of the population likely only needs to use SPF 15 or 30.

How to be sun safe

  • Regardless of the SPF selected, sunscreen must be reapplied every two hours. Reapply after being in the sun, sweating or after submersion in water.
  • Apply sunscreen 30 minutes before going into the sun. This will ensure the lotion is absorbed by the skin before you’re exposed to sun rays.
  • There are many skin care and makeup products that have added an SPF element for skin protection benefits. Using SPF based products daily can protect your face from the aging effects of sun damage.
  • To avoid sun exposure, clothing such as a hat or long sleeve shirt can act as an effective barrier. Staying out of the sun completely is also an option.


For a full scientific description of why sun safety is important, visit Hemingway Medical Spa.


If you have accumulated sun damage or have any suspicious moles that need to be checked, please consult your family physician or dermatologist for a skin exam.