Are You Using Enough Sunscreen?

Summer in the U.S. brings extended, leisurely days spent at beaches, pools, or theme parks — enjoying outdoor activities under the intense summer sun. While many of us know to use a sunscreen with SPF 30 or higher during peak sun exposure, a new study reveals that we often apply it too thinly, reducing its effectiveness by up to 40 percent.

Sunscreen's effectiveness is measured by its sun protection factor (SPF), with SPF 30 blocking 97 percent of UV rays. Higher SPF offers more protection, though even SPF 100 doesn't completely block all UV light.

According to recent research from University College London, the issue lies in the insufficient amount of sunscreen most people apply to achieve the advertised protection levels. Lead researcher Antony Young notes via email that SPF ratings are determined in labs by applying sunscreen at a density of 2 milligrams per square centimeter of skin.

"An average woman has approximately 1.7 square meters (18.3 square feet) of skin," Young states. "For full-body coverage, she would require about 33 grams (1.1 fluid ounces) of sunscreen. With three applications daily, this amounts to roughly 100 grams (3.4 fluid ounces)."

To put this into perspective, 1 fluid ounce is about the volume of a shot glass, and a standard large sunscreen tube contains only 8 fluid ounces. This means a single person spending an entire day in the sun would need nearly half a tube for adequate protection.

Are you applying that much sunscreen? Likely not. Additionally, the texture and feel of such an amount might not be appealing.

Young and his team estimate that in everyday use, people apply sunscreen at a density of around 0.75 milligrams per square centimeter, which is less than 40 percent of the recommended amount. Consequently, the 97 percent protection claimed by SPF 30 products is far from being achieved.

The encouraging finding from Young's research is that higher SPF products, such as SPF 50 or above, can still offer significant protection even when applied sparingly. He discovered that applying just 7.5 milligrams of SPF 50 sunscreen per square centimeter in real-world conditions still provided "substantial DNA protection" compared to skin left untreated.

Real-world Sunscreen Strategies

Does this imply you should rush to purchase the priciest SPF 100 or slather your SPF 30 as thickly as cream cheese on a bagel?

You could, according to Ivy Lee, a board-certified dermatologist in Pasadena, California, but the most effective daily sun protection plan is one that’s practical and sustainable.

"I advise my patients to choose the highest SPF that feels comfortable for everyday use," Lee explains. "How can anyone be sure they’re applying exactly 2 milligrams per square centimeter? It’s impossible. The goal is to avoid causing stress over this and instead foster consistent, healthy habits."

In the United States, skin cancer ranks as the most prevalent form of cancer, with ultraviolet (UV) light exposure being a significant risk factor for all types, including melanoma. The American Academy of Dermatology (AAD) estimates that over 9,300 Americans will lose their lives to melanoma in 2018.

UV light exposure without protection harms the DNA in skin cells, increasing the likelihood of skin cancer. This damage can stem from either a few intense sunburns or prolonged, cumulative sun exposure. Shockingly, the AAD states that experiencing five or more blistering sunburns between the ages of 15 and 20 can raise your melanoma risk by 80 percent.

Adopting healthy sun protection practices involves staying out of the sun during peak hours from 10 a.m. to 2 p.m., wearing a wide-brimmed hat and sunglasses when outdoors, and applying sunscreen to all exposed skin, even on cloudy days.

For comprehensive protection, Lee advises starting the day with a cream or lotion sunscreen, ideally applied 15 to 30 minutes before going outside. Rather than measuring a precise amount, Lee encourages her clients to treat sunscreen application like a massage, ensuring thorough coverage without missing any areas. Since body sizes and product textures vary, there’s no one-size-fits-all quantity.

Lee recommends using spray or powder sunscreens for quick touch-ups while on the move. While reapplying every two hours is ideal, she suggests a more practical approach of reapplying around lunchtime. If you’re near water, sand, or snow, more frequent reapplication is necessary due to the reflective nature of UV rays on these surfaces.

What about individuals with naturally darker skin tones? Is the same amount of sunscreen necessary? Lee explains that while skin cancer is less common among people of color, UV exposure can still lead to premature aging. Using sunscreen daily helps reduce wrinkles and age spots, benefiting all skin types.