What Is SPF? The History and Science Behind Sunscreen

Every skincare expert will tell you to wear sunscreen — copious amounts of it — to protect your skin from all sorts of damage. You're probably aware of its benefits, such as preventing premature skin aging. However, all the rules and jargon can still get confusing. What is SPF? How much of it do we need? What the heck are UVA and UVB rays? Which one should you worry about? Here’s your guide to understanding sunscreen once and for all. 

As early as 3100 B.C., people have been using forms of sun protection, albeit primarily for cosmetic reasons. In ancient Egypt, lighter skin was more desirable culturally, leading the Egyptians to use rice barn, jasmine, and lupine to prevent skin darkening. The National Library of Medicine notes that it was only in recent years that researchers discovered the UV light-fighting benefits of these ingredients.

Ultraviolet rays were discovered in 1801 by German scientist Johann Ritter, making it possible to understand how sunburn works and how to protect the skin against it. The 2004 book Photoaging credits chemist Milton Blake as the inventor of sunscreen in 1932. He created the first sunscreen product, which was popular in Australia. More varieties of sunscreen have mushroomed since. In 1938, someone came up with a “glacier cream” with only SPF 2! Waterproof types were created in 1977.

In 1978, the US Food and Drug Administration mandated that all sunscreens needed to be labeled with an SPF rating to protect consumers. They define SPF or sun protection factor as a measure of how much UV energy (solar radiation) can cause sunburn on sunscreen-protected skin. The higher the SPF value, the more protection you get. 

The SPF rating does not have anything to do with how much time you get to spend under the sun or how often you need to reapply. Although the amount of solar energy exposure does increase the longer you stay under the sun, there are other factors to consider, such as the intensity of exposure at any given time.

For example, one hour of exposure at 9:00 a.m. and 15 minutes at 1:00 p.m. subjects your skin to the same amount of solar energy (U.S. FDA). Take note that your skin type, the amount of sunscreen you applied, and how often you reapply also affect the amount of UV energy you are exposed to.

In the simplest terms, the SPF rating allows you to compare the protection that you are getting between products. The Skin Cancer Foundation recommends an SPF rating of at least 30. According to the American Academy of Dermatology (AAD), SPF 15 filters 93 percent of UVB rays, while SPF 30 filters 97 percent.

The highest available SPF in a sunscreen product is SPF 100. However, according to Penn State Prevention Research Center, you don’t need that much. Their studies show that reapplying throughout the day provides more protection.

Sunscreen usually contains a mix of organic and inorganic chemicals. Organic chemicals include zinc oxide and titanium dioxide, which act as a “physical” sunblock. They reflect the sun’s UV rays and are often responsible for the dreaded white cast in the past. These days, products can have these ingredients minus the white cast by making smaller particles.

Not all “physical” sunscreens are 100% mineral-based. Some can also contain chemical ingredients, which you shouldn’t be afraid of. Inorganic ingredients often referred to as “chemical,” include oxybenzone and avobenzone, which absorb UV light and release it as heat. Since these don’t just sit on top of the skin, they provide better protection during sweaty, physical activities.

The purpose of SPF sunblock or sunscreen is to block and absorb as many UVA and UVB rays as possible through a combination of ingredients. These two types of ultraviolet rays are proven to contribute to the risk of skin cancer. Ultraviolet B rays have a shorter wavelength and cause sunburn. Ultraviolet A rays have a longer wavelength and are associated with photoaging. A third type — UVC rays — have the shortest wavelength, but they are absorbed by the ozone layer and do not reach the Earth.

According to University of Iowa research, the sun has approximately 500 times more UVA rays than UVB rays. UVA rays also penetrate the skin at a deeper level. The Skin Cancer Foundation also notes that more than 50 percent of UVA rays can penetrate through glass. Most sunscreen products protect the skin against UVB rays (sunburn). The AAD recommends broad-spectrum sunscreen since it protects the skin from both UVA and UVB rays. 

If you can’t find the term “broad spectrum” on the label, check for a PA rating — which refers to the amount of protection you get specifically from UVA rays. If the product has this rating, this means it protects the skin from both UVA and UVB rays. The plus signs indicate the level of protection. Currently, the highest rating is PA++++, but not all countries have updated. The PA (Protection Grade of UVA) grading system originated in Japan. Later, other countries started adding PA grading on the label in addition to the SPF rating.

Speaking of labels, be wary of sunscreen products that claim to be waterproof. The AAD warns that there is no such thing. Sunscreen can, however, be water-resistant. The product will stay effective in water for either 40 or 80 minutes (usually indicated on the label). After this period, you’ll need to reapply.

Apply sunscreen on dry skin, approximately 15 minutes before being in the sun. This includes indoor and outdoor exposure. The AAD recommends one ounce of sunscreen (one shot glass) to cover the entire body. Concentrate on areas unprotected by clothing, especially the face, neck, chest, ears, tops of the feet, arms, and legs. Use a lip balm with SPF to protect your lips. Reapply every two hours.

If you’re wondering how much sunscreen you need to apply to your face, just remember, there is no such thing as too much sunscreen. So, when in doubt, apply more. However, if you want to be precise about it, use two milligrams of sunscreen per square centimeter of skin.

POND'S UV Bright Sunscreen is a broad-spectrum sunscreen that provides maximum protection minus the white cast. It’s suitable for most skin types and contains skin-brightening ingredients like Gluta-boost and niacinamide, which help even out the skin tone. If you're looking for SPF products that can also restore dry skin, use Vaseline Healthy Bright SPF24 PA++ Sun + Pollution Protection Body Lotion all over your body. It provides both SPF and brightening benefits. Thanks to Vaseline Petroleum Jelly in its formula, it also deeply moisturizes the skin.

The history and science behind skincare products can provide a deeper appreciation of what you apply to your skin. Now, you can stop asking yourself, “What is SPF?”, and start using it to your skin’s full advantage.