Sunscreen Explained

In honor of Skin Cancer Awareness Month, we want to lay it on thick (pun intended) when it comes to your education around sunscreen. We hope to answer your questions and gear you up for a healthy and safe summer, so here goes: Sunscreens Explained.

Do you understand how sunscreens work? What does it mean to be a broad spectrum sunscreen? What is the difference between a chemical sunscreen and a physical sunscreen? What does SPF (Sun Protection Factor) mean? Are sunscreens toxic? Do you have to wear sunscreen everyday? Will I still get enough Vitamin D if I wear sunscreen? How much sunscreen should I apply?

How do sunscreens work?

Sunscreens are products that have been developed and marketed to help block the damaging effects of ultraviolet radiation from the sun, including both UVA and UVB rays. Sunburn is mostly caused by UVB rays while UVA rays are the chief culprit in wrinkles, leathering and photoaging. Typically all sunscreens vary in their ability to block these two types of ultraviolet radiation. A broad spectrum sunscreen offers protection against both UVA and UVB rays.

How do they block this UV radiation? In 2 ways – through organic and inorganic ingredients. The inorganic ingredients like zinc oxide and titanium dioxide work as physical sunscreens. In other words, they reflect the UV rays in the same way that white paint reflects light. Remember that thick white pasty stuff you would see on the noses of lifeguards at the beach? That is zinc oxide. Only now, manufacturers can make these physical sunscreens with much smaller particle size, so the sunscreen isn’t nearly as pasty. Whew – mama doesn’t need ashy skin this summer.

On the other hand, the organic ingredients like oxybenzone and avobenzone of chemical sunscreens actually absorb UV radiation through their chemical bonds. As the bonds absorb the radiation, the sunscreen breaks down and releases heat. Most sunscreens use a combination of chemical and physical sunscreens.

What is SPF (Sun Protection Factor)?

Does a higher SPF mean more protection from that awful ultraviolet radiation? Well, sort of. SPF stands for Sun Protection Factor and is a measure of the product’s ability to UVB from damaging the skin. And that measure is calculated in time in the sun. For example, if you tend to burn in the sun in 20 minutes without any protection, an SPF 15 product would protect you 15x longer, or 5 hours. Another way to read SPF numbers is a measure of the amount of UVB rays are filtered out; for example SPF 15 filters out about 93% of the UVB rays, SPF 30 filters out about 97% of UVB rays and SPF 50 filters out about 98% of the UVB rays. No sunscreen will be 100% effective in blocking UVB rays.

The downside to SPF – it doesn’t say anything about a products effectiveness on blocking UVA rays, which cause more of the photo aging of the skin, and may have a secondary effect on cancer. UVA radiation penetrates deeper into the skin, and the only type of sunscreen that can effectively help block UVA rays are physical or inorganic sunscreens made with zinc oxide or titanium dioxide.

What’s worse – the sun or sunscreen?

There is growing debate on the safety of sunscreen use in recent years, especially given the fact that the American Academy of Dermatology and the Skin Cancer Foundation recommend daily use of sunscreen. Can the added exposure to potentially toxic chemicals everyday over a lifetime of 80-90 years cause greater harm than the ultraviolet radiation of the sun?? The short answer – yes and no. The upside – you don’t have to choose.

The chemicals in many sunscreens that are organically derived especially the benzophenones like oxybenzone are absorbed into the skin and have been found in the urine. It promotes DNA damage in the presence of sunlight. In fact the Environmental Working Group has commissioned that these ingredients be restricted from sunscreens in the US and recommend that children not use products containing these ingredients as they have been linked to potentially causing more cancers than they prevent. Yikes.

Sunscreens - Mother and Child

Bottom line – stick with physical sunscreens. They block both UVA and UVB rays and they are not absorbed into your skin like chemical sunscreens. Why risk it?!

How much sunscreen do I apply? How often?

For proper sun protection, adults should apply 1 ounce (about the amount in a shot glass) of sunscreen for every application. That is a lot of product. Said another way, one person should use 1/4-1/2 a bottle (8oz) of sunscreen during a full day at the beach. Do you go through that much sunscreen during the summer months? Statistics show that the reason for most sunburns is due to 3 reasons – the proper amount of sunscreen wasn’t applied, sunscreen wasn’t reapplied every 2 hours as recommended, or expired product was used. Just one sunburn doubles your chances of melanoma, the deadliest form of skin cancer.

And let’s get real, you really should be wearing sunscreen everyday. Even if we just drive to and from and office everyday, that is a considerable amount of sun exposure. In fact that minimal amount of sun exposure supplies us with all the Vitamin D we need everyday. So don’t fall for the argument that you shouldn’t wear sunscreen because we need Vitamin D…you will get your Vitamin D from the sun or from other sources. Don’t reserve sunscreen use for the summer or just beach days. UV radiation is fairly intense the winter especially on the side of ski slope or even on a crisp fall afternoon during a hike.


Cloudy days are no exception. Up to 40% of the sun’s ultraviolet radiation reaches the earth on a completely cloudy day. Believe me – you don’t want to be the one with a child that has a sunburn from playing all day outside on a cloudy day.

In honor of anyone that you know or have lost to cancer, now that you know more about sunscreen, please take our stance and do better. It is your responsibility. Please share your thoughts and comments with us, and share this post with everyone you love.




Skin Cancer Foundation