As temperatures climb and sleeves grow shorter, a familiar ritual returns: slathering on the sunscreen – or perhaps skipping it. Confusion lingers about how to protect our skin from the sun.
Do we need it every day? Are chemical ingredients safe? What SPF do I need? What even is SPF, aka sun protection factor?
Debates unfold on social media and store shelves fill with products labeled “mineral,” “reef-safe,” and “SPF 100,” while many people are left guessing what the science supports.
Sunscreen is one of the most widely recommended and commonly misunderstood products in medicine. Though dermatologists broadly agree on its benefits, questions about safety, ingredients, regulation and necessity persist – often fueled by online misinformation and decades of uneven product labeling and testing standards.
To clarify what the science shows, we spoke with Stanford Medicine dermatologists who discuss these issues every day with their patients. Their consensus: Sunscreen is a safe, essential tool for preventing skin cancer, other skin disorders, and the overall effects of aging on the skin. But not all products are created equal, and public understanding of sunscreen is overdue for an update.
The background
While the sun’s rays provide our planet with vital warmth and life-sustaining energy, they also have a downside: Ultraviolet (UV) radiation can penetrate our skin and damage our cells. UV light is divided into UVA and UVB based on the wavelength of the radiation. UVB rays cause direct DNA damage that can lead to mutations and skin cancer. UVA rays, which have a longer wavelength, can penetrate deeper, generating oxidative stress and inflammation that contribute to wrinkles and uneven skin tone, as well as skin cancer.
“Most people know that sunscreen can help prevent sun-related skin cancer, but they don’t know the impact on photo-aging,” said Zakia Rahman, MD, a clinical professor of dermatology. “A lot of people want their skin to look better, and UV light really accelerates premature aging of the skin.”
For centuries, people have experimented with ways to protect their skin from the sun – rubbing on plant oils, muds, or minerals to block or reflect its rays. Modern sunscreen formulations, however, are rooted in mid-20th-century chemistry, when scientists first identified specific compounds that could reliably filter ultraviolet radiation.
Today, there are two main categories of sunscreen ingredients:
- Chemical filters that absorb UV rays into the skin and deactivate them. Chemical sunscreens, including ingredients like avobenzone and octocrylene, tend to provide broader UVA and UVB coverage than do mineral sunscreens.
- Mineral filters (also known as physical filters) that deflect and scatter UV rays. Mineral sunscreens are less likely to cause irritation but some – especially those containing titanium oxide – block mainly UVB radiation.
The debate
Concerns about sunscreen ingredients, effectiveness, and necessity are not new, but they’ve gained traction in recent years. Some consumers worry that chemical filters could act as hormone disruptors or cause allergic reactions. Others cite vitamin D deficiency or a desire for a “base tan” as reasons to skip sunscreen altogether.
There are also questions about how sunscreens sold in the U.S. compare with those available elsewhere. Because the U.S. Food and Drug Administration classifies sunscreen as an over-the-counter product, receiving approval for new UV-blocking chemicals is slow and expensive. As a result, the U.S. has fallen behind countries like those in the European Union, where sunscreens can be more quickly approved for sale as a cosmetic, and newer sunscreen ingredients such as Tinosorb, Mexoryl, and Uvinul are widely used.
“Sunscreen technology abroad has resulted in the development of 30 UV radiation (UVR) filters, many that extend to the ‘far UVA’ wavelength, compared with only 17 FDA-approved UVR filters in the U.S., despite similar safety standards,” explained Susan Swetter, MD, a professor of dermatology. “The best sunscreens abroad contain Tinosorb, Mexoryl, or Uvinul – none of which are currently FDA-approved.”
With dermatologists admitting that U.S. sunscreens are inferior and headlines claiming that many sunscreens contain dangerous chemicals or are bad for the environment, how should you choose a sunscreen?
What the science says
Scientific studies have consistently shown that regular sunscreen use reduces the incidence of skin cancer and slows the signs of aging.
A randomized controlled trial in Australia found that daily use of sunscreen reduced the incidence of melanoma by 50%, while a Norwegian study found that using at least 15 SPF sunscreen lowered melanoma risk by 30%. Other studies have shown that regular sunscreen use can reduce the risk of other skin cancers, including squamous cell carcinoma, basal cell carcinomas, and keratinocyte carcinomas.
“Our general advice is to wear sunscreen whenever possible – in California, that means most months of the year – and to use other physical protection from the sun as well, like clothing, hats, and sunglasses,” said Joyce Teng, MD, PhD, a professor of pediatric dermatology.
For sunscreen to work, though, it must be applied correctly, and that’s where many people fall short.
“It’s like painting a wall with a fine mist versus using a roller,” Teng said.
Because of people’s tendency to apply too little sunscreen, Rahman recommended going with a higher SPF rating than you might otherwise – this way, you end up with adequate protection. She also pointed out that SPF ratings are not linear: An SPF of 15 offers protection from about 93% of UVB radiation, while SPF 30 blocks 97% and SPF 50 blocks 98%.
“A lot of my patients find higher SPF sunscreens to be greasier or more irritating,” she said. “It’s a misconception that you have to go with a super high SPF to get a benefit; if a lower SPF is what you’re happy wearing, then that is better than not wearing sunscreen.”
“It’s really important to use a good, thick layer of sunscreen,” Teng said. “If an active teen or adult has a 6- or 8-ounce bottle of sunscreen they’re using all summer, there’s no way they’re using enough. If you’re outside regularly, that bottle should last about two weeks.”
Spray formulations may be convenient, but they often result in uneven coverage.
An SPF of 15 offers protection from about 93% of UVB radiation, while SPF 30 blocks 97% and SPF 50 blocks 98%.
For consumers worried about hormone disruption, no definitive link has been established in humans; the concern stems mostly from animal or lab studies at high concentration. But many dermatologists say the ingredients in sunscreens can cause skin irritation in some people.
“Sunscreen has a lot of preservatives in there to stabilize them,” Teng said. “Some of those preservatives are activated in the sun, and they can cause sensitivity and allergic dermatitis.”
She recommends looking for fragrance-free and additive-free mineral sunscreen in these cases.
When patients express concern about sunscreen blocking their absorption of vitamin D, Teng reassures them that there’s no need to choose between skin health and adequate vitamin levels.
“You can absolutely get enough vitamin D through diet and supplements,” she said.
While UVB exposure helps the body synthesize vitamin D, the amount blocked by regular sunscreen use is minimal – and most people are still exposed to enough incidental sunlight to maintain healthy levels. For those at risk of deficiency, dermatologists recommend dietary sources like fortified dairy, fatty fish, or a simple supplement rather than forgoing sun protection.
Where does that leave us?
Even the best sunscreen isn’t foolproof. It needs to be reapplied every few hours, doesn’t block all UV rays, and works best in conjunction with shade and sun protective clothing. But when used properly, it’s one of the most effective tools available for reducing the burden of skin cancer and minimizing long-term skin damage.
Ultimately, the choice of a sunscreen is based on personal factors: Do you have sensitive skin? Do you care about slowing the effects of aging on the skin alongside cancer prevention?
Both mineral and chemical options can be effective if they offer broad-spectrum protection and are used properly. Mineral sunscreens may be preferred by people with sensitive skin or concerns about ingredient absorption. Chemical sunscreens, meanwhile, tend to be easier to apply evenly and provide better coverage against long-wavelength UVA rays.
“The best sunscreen is the one you’ll use regularly,” Teng said.
She added that any good sunscreen should be labeled “broad spectrum,” the FDA designation that it offers both UVA and UVB protection. For consumers looking for the most advanced protection, Swetter suggests ordering sunscreen from abroad.
Despite the risks of UV exposure, the dermatologists still encourage their patients to go outside – just with protection.
“I don’t want to prevent anyone from spending time outdoors,” Teng said. “It’s incredibly important to your overall fitness, your cardiovascular health and your endorphins. You just need to think about minimizing the risks from UV light.”
For more information
This story was originally published by Stanford Medicine.
Writer
Sarah Williams
