Enjoying Outside - How Sunscreen Works

Kristie Erhardt • August 9, 2024

Photo: Holtenwellness.com

 

Ultraviolet (UV) light or radiation is a form of energy from the sun. On the electromagnetic scale, UV light has shorter wavelengths than visible light, which is why humans can’t see it, but longer wavelengths than X-rays. However, we can most definitely feel it; UV light is what causes sunburns, suntans and freckles, as well as more serious skin and eye diseases. Thankfully our atmosphere, primarily our ozone layer, filters out a lot of this radiation which is why reducing and minimizing impacts to air quality is so important. There are many types of ultraviolet light but the four most commonly known are: UVA, UVB, UBC and Near-ultraviolet. UVA has the longest wavelengths of the UV lights and is primarily associated with skin aging. It is not absorbed by the atmosphere at all and can penetrate deep into the middle layer (dermis) of the skin. UVB has shorter wavelengths than UVA and is associated with skin burning and affects mainly the outer layer (epidermis) of the skin. Much of the sun’s UVB is absorbed by the atmosphere. UVC has the shortest wavelength and is useful as a germicide. In nature it is completely absorbed by the atmosphere. Near-ultraviolet light is visible to insects, fish, some birds and some mammals. UVA and UVB have been proven to harm the DNA in skin cells leading to an increased risk of damage, premature aging and possibly even skin cancer. Exposure to UVA and UVB light can also cause eye damage such as cataracts and some cancers. However, some UV light is beneficial. Exposure to UVB is responsible for the formation of vitamin D and in some climates or locations that don’t have abundant sunlight, vitamin D may need to be supplemented. UVC is known to kill active microbes such as viruses and bacteria. Recent work has indicated that use as a germicide may make indoor air as pure as outdoor air which could greatly lessen the transmission of viruses in indoor settings such as schools and hospitals.     

 

Thankfully for those of us that like to spend extended time outdoors, modern science has gifted us with sunscreen that can help prevent sun damage while we play or work outside. Although there are different types of sunscreens and they work in different ways, their main objective is to prevent UVA and UVB radiation from reaching the surface of your skin. 

 

Physical sunscreens contain very finely ground minerals such as zinc oxide or titanium dioxide that physically sit on the surface of the skin and act as a shield to reflect the sun’s rays away from our skin. The minerals are what causes most mineral sunscreen, sometimes called sunblock, to be a dense consistency and look white on the skin. Physical sunblocks work extremely well and rarely cause irritation or allergic reactions (both zinc oxide and titanium dioxide are main ingredients in diaper rash creams) and it's these types of sunscreens that are considered reef safe or reef friendly because they aren’t leaving added chemicals in the ocean.

 

The ingredients in chemical sunscreens create a thin film on the skin that absorbs the ultraviolet radiation before it reaches the surface skin. These sunscreens are usually clear or rub in to be invisible which is more appealing to a lot of people but can cause stinging or irritation to the skin. These types of sunscreens usually contain about 20% of the active ingredient and the rest is emollients, stabilizers and fragrances which are responsible for the irritation for some people. Chemical sunscreens come in a variety of formulas from gels, creams, lotions and sprays.

 

Sun Protection Factor (SPF) is a way to measure how effective that sunscreen or block is. It is a measure of how much UV light gets to the surface of your skin. As it would seem, the higher the SPF number, the higher the protection factor. That doesn’t mean that you can stay out in the sun longer without reapplying though, it simply means that it’s filtering out more or less of the UV rays. An SPF of 30 allows about one-thirtieth (or 3.3%) of the UV to reach the surface of your skin which means that it filters about 96.7% of the UV light. Doctors and those in the skin care industry recommend a sunscreen with at least an SPF of 50 or greater.

 

Broad spectrum sunscreens provide protection from both UVA and UVB light. Many broad spectrum sunscreens are a combination of both physical and chemical blockers and are the most effective sunscreens. Sunscreen should be applied 15-30 minutes before going out in the sun and reapplied at least every two hours or more frequently after swimming, sweating or towel drying. Sport and water-resistant sunscreens should stay on wet skin and be effective for 40-80 minutes. All sunscreen should also be applied liberally; at least a teaspoon for the face and neck, another teaspoon for each arm and leg, another for the front and another for the back of the body. A good estimate is about a shot glass worth of sunscreen for your entire body. And don’t forget to do your ears, they take a beating sitting out there on their own. There are even specific sunscreens available for your hair and scalp.

 

In general, sunscreens are considered safe as long as you’re not allergic to any ingredients and it’s best to use sun protection daily, even on cloudy days. Water, sand and snow reflect sunlight and can result in a nasty and unexpected burn. For babies under six months of age, doctors recommend clothing and hats with SPF rather than sunscreens that can irritate their delicate skin.

 

So slather it on, front and back, top to bottom, and go enjoy the outside!

RECENT ARTICLES

By Nate Lillge August 26, 2025
The 19th Amendment to the Constitution - granting women the right to vote - was certified on August 26, 1920. In commemoration of this, in 1973 Congress designated August 26 as "Women's Equality Day" to remind us of the heroic women who advanced the Women's Suffrage movement. In recognition of Women's Equality Day, Tuleyome is highlight two women who are dedicated to our public lands: Jennifer Onufer (Bureau of Reclamation), Kay-Leigh Barnitz (Bureau of Land Management), and Laura Leidner (US Forest Service). Hear about Jennifer's journey below and learn about Kay-Leigh here and Laura here . Thank you, Jennifer, for your passion and dedication to our public lands! I accepted a lateral transfer to the Bureau of Reclamation at Lake Berryessa after working 10 years with the National Park Service. Seven of those years were at Grand Canyon National Park. Working for Reclamation was never my dream however, I always respected that the agency’s mission to deliver water and power benefited a variety of people from diverse walks of life. As a child, I visited National Parks with my family and became enamored with how uniformed National Park Service staff would perform a variety of duties like staffing a visitor center, cutting grass, or demonstrating how to fire a Revolutionary War Cannon (with or without making it clear that the cannon wasn’t about to take my arms off!). I liked the diversity of tasks in this line of work. I started work at Lake Berryessa in July 2015 as a GS 09 Park Ranger and eventually became the sites’ Supervisory Park Ranger in 2018. I maxed out the available Park Ranger Series positions at Berryessa and took a position with the National Park Service at San Francisco Maritime National Historical Park in 2022 before earning enough time in grade to qualify, compete, and earn a chance to serve as Lake Berryessa’s Park Manager in January 2024. My predecessor, Margaret Baily [has inspired me]. I always appreciated being able to discuss and troubleshoot ongoing topics with her. While a Park Ranger at Grand Canyon, we received a grant from the National Park Foundation to create the Grand Canyon Active Trails program to promote trail use among local residents. This project became a great outdoor laboratory for trying new outdoor hikes, walks, and bike rides. My most rewarding program was a walk of an old South Rim burn area that took people through the timeline of that incident, its causes, the challenges, and its conclusion. It was the last hike I had the privilege of leading at Grand Canyon before transferring to Berryessa. 2020 was a very rough year professionally, and personally. If I had to go back and do it again, I’d have placed more of a priority on my family. What advice would you give young women starting their career: It’s convoluted, but I have to regularly remember to “forget to say I can’t” as often as possible.
By Nate Lillge August 26, 2025
The 19th Amendment to the Constitution - granting women the right to vote - was certified on August 26, 1920. In commemoration of this, in 1973 Congress designated August 26 as "Women's Equality Day" to remind us of the heroic women who advanced the Women's Suffrage movement. In recognition of Women's Equality Day, Tuleyome is highlighting three women who are dedicated to our public lands: Kay-Leigh Barnitz (Bureau of Land Management), Jennifer Onufer (Bureau of Reclamation), and Laura Leidner (US Forest Service). Hear about Kay-Leigh's journey below and learn about Jennifer here and Laura here . Thank you, Kay-Leigh, for your passion and dedication to our public lands! I received my Bachelor of Science degree from New Mexico State University. My focus area was wildlife habitat management, rangeland science and I minored in biology. Prior to graduation I was offered a Direct Hire Authority – Resource Assistance Internship (DHA-RAI) from the BLM Las Cruces District Office. This internship lasted 3 months and awarded me non-competitive hiring status with the Department of the Interior. When I graduated, I had already been offered a job with the Ukiah Field Office as a wildlife biologist. I started with the BLM in Las Cruces New Mexico as an “Environmental Reclamation Specialist” which was just a fancy title for picking up illegal trash dump sites. It wasn’t much but it was an opportunity to get my foot in the door. I took pride in cleaning up public lands, and I believe that showed. Shortly thereafter I was offered a job on a contract with the New Mexico Associate of Conservation Districts as a Technical Assistant for the BLM LCDO and I worked there for 3 years as a part time employee while going to school. I was able to help with all Natural Resources work in the office and in the field including grazing bills, grazing allotment inspections, endangered species conservation, and more. This position gave me a great interdisciplinary background and set me up for success later in my career. My grandfather was a Forest Service Ranger and my uncle was a wildlife biologist for the BLM. I always knew I wanted to be a wildlife biologist, but I wasn’t sure how to make it happen and I didn’t much mind what agency. The DHA-RAI program allowed me the opportunity to pursue a position with the BLM. My childhood was spent outside. We ran to the hills to escape the modern conveniences of society and connect with the landscape and public lands. My dad, brothers and I spent many Sundays at “church” in the mountains. My family has always been connected to public lands and once I realized I could make a hobby or passion of mine a career, I followed the paths to make that a reality. My grandfather, my uncle and my father are my biggest inspirations. They have worked harder than anyone I’ve met to do the right thing for the land and people. Some of my earliest memories of my grandfather involve him sharing the scientific names of the native plants he grew in his yard. Since then, I’ve loved learning the scientific name of every plant I see. In college my uncle raised federally threatened Chiracahua leopard frogs in his backyard and I’d help release them on BLM managed lands. My father raised me and my two brothers as a single parent, I don’t know how he managed but I think we all turned out pretty dang good. I strive every day to remember their words, their work ethic and advice. I am most proud of my work with partners to achieve things I never thought possible on my own. When I started here in Ukiah I was the only natural resources employee with a lot of natural resource issues (weeds, degrading riparian systems, etc). The community that I’ve fostered through collaboration with partners is rewarding especially when it lends to on the ground action and change. The things I’ve achieved in Ukiah would’ve never been possible without partnerships. One of my favorite memories is the day we started construction of the Garcia River Estuary Salmonid Habitat Enhancement Project with The Nature Conservancy and the Stornetta Ranch. I’d worked for 5 years to see the day. It was rewarding to finally see the fruits of all the hours spent at meetings and planning. Now salmonid species like Coho salmon have thrive in the estuary since construction was completed. I have had an internal hurdle I have to work to overcome every day. I doubt myself and get imposter syndrome. Like, who put me in charge? However, it is ok to not know everything, to be imperfect. When you foster a community of people with expertise and knowledge you can reach out and lean on them for help. My grandfather always said, “You were fit with two ears and one mouth, therefore you should listen twice as often as you speak.” When starting my career I listened to everyone who would take the time to share with me their experiences, their work, and their ideas for the landscape and future. It is important to hear everyone’s perspective even those you may not agree with. You can learn something from everyone in every conversation if your only goal is to listen. This doesn’t mean you shouldn’t speak up when you feel you should. Trust yourself, your knowledge and expertise. Your voice matters.
By Nate Lillge August 26, 2025
The 19th Amendment to the Constitution - granting women the right to vote - was certified on August 26, 1920. In commemoration of this, in 1973 Congress designated August 26 as "Women's Equality Day" to remind us of the heroic women who advanced the Women's Suffrage movement. In recognition of Women's Equality Day, Tuleyome is highlighting three women who are dedicated to our public lands: Laura Leidner (US Forest Service), Kay-Leigh Barnitz (Bureau of Land Management), and Jennifer Onufer (Bureau of Reclamation). Hear about Laura's journey below and learn about Kay-Leigh here and Jennifer here . Thank you, Laura, for your passion and dedication to our public lands! I went to the University of Georgia and studied English, mostly because I enjoy writing. After college I worked for small businesses and startup companies doing websites and social media marketing. I eventually landed a communication job at the Centers for Disease Control and Prevention and worked in public health for seven years. After camping and hiking in national forests and parks in the Southeast, I became curious about working for public lands and started looking for opportunities. In 2021 I transferred to the Forest Service to a public affairs position with the Mendocino National Forest. One perk of being a federal employee is that there are hiring paths that allow you to transfer to other agencies (if you meet the qualifications of that position). I grew up in South Georgia where my parents owned a 60-acre pine tree farm with several creeks, ponds and wetlands. Stewardship of the land was something ingrained in me as a kid, though I’m sure I didn’t appreciate it at the time. I think because I grew up in a rural place surrounded by trees, I have always felt inspired by landscapes and nature. It is amazing to me that part of my job is being out in the field visiting project sites and talking to the public about the activities and places they love. Public lands offer many job opportunities that appeal not only to people who love the outdoors but to people who crave the feeling of wanting to make an impact. I’m currently the Public Affairs Officer on the Mendocino National Forest, which is the eastern spur of the North Coast Range in Northern California. This September will mark four years that I’ve been in the position. I have also done several short-term assignments as a public information officer on wildfire incidents in California, including on the Tahoe National Forest, San Bernardino National Forest, Angeles National Forest, and Sequoia National Park. My job is to provide the public with information they need from emergency safety info to some of our fun programs like Every Kid Outdoors and Christmas Tree permits. I love to visit our forest’s project sites, host educational booths at community events, visit schools, meet partners, and assist neighboring forests. My parents are my biggest inspiration. My mom was a federal employee and a district conservationist for the Natural Resources Conservation Service, and my dad was an agricultural journalist who wrote for Progressive Farmer and other farming magazines. They both served their communities and helped people tend the land. The most profound project I’ve been involved with is the Nome Cult Walk, which happens each September to commemorate the path of Native Americans who were forced to march from Chico to Covelo over the North Coast mountains in 1863. In 2023 I collaborated with the Nome Cult Walk Cultural Committee and the Forest Service’s Region 5 videographer Andrew Avitt to produce a short video and companion story about the walk. Imagine walking across the Sacramento Valley in the high temperatures of September, ascending the unforgiving foothills, feeling the sorrow of being separated from your homeland and family. It is a humbling experience. The healing, hope and resilience of the people who carry on the Nome Cult Walk tradition move me deeply, and it’s been honor to walk with them on the journey. (You can watch the video on YouTube and read the story online .) I have an extremely inconvenient fear of heights. I try not to let it hold me back, but it is an ongoing struggle. The best thing that helps me is gradual exposure, plus following all the safety best practices, and focusing on a task. With support from my coworkers, I have made some huge progress when I assisted cone collection at our Chico Seed Orchard, harvesting cones from a lift about 60-80 ft in the air. The first few moments in the lift as it rises to the tree canopy is alarming, but once you are there, clipped in safely, collecting healthy cones is immensely satisfying. Did you know that Ponderosa pines produce their best cones at the crown? Cone collection is an important part of reforestation after severe wildfires. Cones collected at the orchard are processed for their seed. The seed gets tested, saved in a seed bank, and later grown in a nursery for planting future forests. It’s legitimately hard and stressful to figure out a career, how to make money, and be successful. So I first just want to acknowledge that fact. There are so many paths and possibilities, and the path I find myself on is a total surprise to me and I love that. My philosophy has always been to be curious and patient. One thing I appreciate about the Forest Service is that it is an agency that helps you learn on the job and fosters those who show interest. Right now I work in public affairs, but at the same time I’m helping our forester with a project for one or two days a week. Who knows where that might take me?