It’s tempting to constantly reach for sunscreen that comes in a bottle or tube. However, you might be able to rely on a different type of sunscreen—a natural mechanism that develops as your skin is gradually exposed to the sun.
A telltale photo in a review published in Experimental Dermatology shows an arm that got sun exposure shortly after a cast was removed—red skin perfectly fills in where the cast previously wrapped around the lower thumb, across the middle of the back of the hand, and midway up the arm. The rest of the arm shows no sign of sun exposure.
“This implies that the skin will adjust to the sun exposure from your daily routine,” Frank de Gruijl, a retired associate professor of dermatology and author of the review, told The Epoch Times.
Getting smaller, regular doses of sun allows mechanisms in your skin to protect you from the sun’s ultraviolet radiation, making spring the perfect opportunity to incrementally build up your sun tolerance and potentially lower the risk of summer sunburns.
How Skin Works as Sunscreen
What looks like a tan is really the result of an ongoing construction project in the skin.
When the sun hits your skin, pigment cells called melanocytes get busy making melanin—a protective pigment—into little packets that travel to the surface, creating a microscopic shield. Scientists call them supranuclear caps, which primarily absorb ultraviolet radiation and dissipate it as heat, while also scattering some light and helping protect DNA from damage. A microscopic thickening—the accumulation of cells—of the outer skin layer adds another layer of defense.
Scientifically speaking, this process is called photoadaptation of the skin. It’s hard to quantify, de Gruijl noted, but its effects can be observed in the skin of outdoor workers across the globe.
A meta-analysis published in the European Journal of Cancer found that although sunburn with intermittent sun exposure—such as during a winter beach vacation—increases melanoma risk, there’s an inverse, protective association among those with chronic, occupational sun exposure. Regular exposure appears to trigger a different biological response.
“This importantly protects against high-dose exposures,” de Gruijl said. “Even in untanned skin, the immunological shifts and further processes—for example, enhanced DNA repair—make the skin less sensitive and less vulnerable.”
Anyone Can Get Sunburn
In the winter, melanocytes become less active in people who aren’t regularly outdoors. That means even someone with very dark skin can burn after prolonged sun exposure following months indoors.
“They’re going to get a sunburn because they don’t have any melanin or melanocytes up in the epidermis to protect them,” Dr. Michael Holick, a vitamin D expert and professor of physiology and biophysics, told The Epoch Times. “But as soon as they’re exposed to sunlight, they instantly begin making it.”
Holick became interested in the skin’s role as a natural sunscreen to help patients maximize their intake of vitamin D, a hormone that is primarily produced through sun exposure and supports bone health. Low vitamin D is associated with autoimmune disease and inflammatory conditions such as Type 2 diabetes, heart disease, and some cancers.
Sunburn can cause redness, inflammation, and damage to skin cells. The rapid shedding of skin that we call peeling is the result of epidermal defects that the body is trying to remove. When damaged cells quickly rise to the surface, the skin sheds or peels.
The more melanin one produces, the more natural sun protection one has. Fair-skinned people with blond or red hair and blue or green eyes burn quickly in the sun and build tolerance more slowly. Nearly half of Americans fall in the middle range of the Fitzpatrick skin phototype scale, which estimates sun sensitivity based on skin tone and tanning history.
What the Risks Look Like
Skin cancer risk is generally lower in darker-skinned people, not only because of pigmentation, but also because of differences in how the skin responds to and repairs UV-induced DNA damage, de Gruijl said.
Whether you can determine your risk of sunburn and skin cancer is debated. The Fitzpatrick classification isn’t the best way to predict someone’s sensitivity to ultraviolet light, according to a study published in Advances in Skin and Wound Care, but it can help estimate overall risk.
“Skin color alone cannot determine reactivity to the sun,” the authors wrote, and they said that multiracial skin is especially difficult to assess.
Regardless of risk, those with skin types two, three, four, and five can all build sun tolerance, Holick said.
The strategy, however, contradicts the American Academy of Dermatology Association guidelines, which recommend using sunscreen with SPF 30 or higher when going outside at any time of day, year-round. The U.S. Food and Drug Administration suggests sunscreen as one part of a broader strategy to reduce sun exposure risks, while noting that some sunscreens may include ingredients that are detrimental to health.
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How to Build Sun Tolerance Safely
There’s no universal guideline that applies to everyone, since each person and day is different. Familiarity with your own skin’s reactions is helpful. For instance, Holick knows he must limit a midday visit to Cape Cod in June to 30 minutes.
His recommendation for midday sun is based on optimizing vitamin D production. For longer periods outdoors, it’s best to limit exposure between 10 a.m. and 2 p.m., when the sun’s rays are strongest.
Alternatively, opt for small daily exposures—about five to 10 minutes—of sunlight, Holick said. He helped develop an app called dminder, which personalizes how much sun exposure you can get based on where you live to maximize vitamin D while avoiding sunburn.
The UV index is a useful guide that indicates how strong the sun’s radiation is on any given day. Besides skin type, burn risk depends on location and the time of year. Because the UV index is a linear scale, a rise from three to seven represents a doubling of UV intensity, meaning the skin needs about twice as much protection or will burn in about half the time, if it hasn’t adapted.
De Gruijl noted that this risk increases when people spend longer than usual in the sun—such as when sunbathing or gardening in early spring before the skin has adapted.
Monitor your skin, gradually increase exposure each day, and give your skin time to adapt, he said. And perhaps resist the urge to use sunscreen—unless you’ll be outside for hours at a time.
“Applying sunscreens daily is not advisable, in my opinion,” de Gruijl said. “It will not allow the skin to properly adapt and will therefore make the skin more vulnerable to sunburn at times one forgets to apply the sunscreen. Apparently, nature has developed a superior strategy.”