Image by Gerd Altmann from Pixabay 

August 27, 2025 - By Sara Bock - sbock@ucsd.edu - This summer, TikTok and Instagram feeds have been full of a new ritual: “checking the UV.” Gen Z content creators are tracking the daily UV index — not to avoid the sun, but to head outside when it’s strongest for what they see as the “optimal” tan. At the same time, some social media influencers are spreading claims that sunscreen is harmful or unnecessary, a trend that has dermatologists increasingly concerned.

While online conversations about sun exposure are trending, the risks of UV radiation are real and cumulative. Peak UV exposure affects all skin tones, from sunburn and premature aging to hyperpigmentation and, in some cases, skin cancer.

To break it all down, we asked Y. Linda Liou, DO, an assistant clinical professor in the Department of Dermatology at UC San Diego School of Medicine, to explain the science of the UV index, the real risks of intentional sun exposure, and how to enjoy sunny days without paying for it later:

This “checking the UV” trend has exploded on TikTok and Instagram. What do you think when you see people timing their tanning — or sun time in general — to the UV index?

I actually love that people are paying attention to the UV index — it means they’re thinking about sun exposure. But what worries me is how it’s being used: instead of avoiding high UV times, people are chasing them to tan faster. A tan may look like a glow, but it’s really your skin’s SOS signal that DNA damage has already happened. You don’t see it right away, but the harm is happening underneath.

What exactly is the UV index, and what does it tell us about sun exposure and skin damage risk?

The UV index is basically a weather report for how strong the sun’s radiation is. It takes into account things like time of day, altitude, cloud cover and ozone levels. The scale runs from 1 to 11+, and the higher the number, the faster your skin can burn or get damaged. At a UV index of 11, for example, some lighter skin tones can burn in under 5 minutes. But even if you are darker skinned and you don’t burn easily, your skin cells are still getting hit with invisible radiation damage.

What are the potential short- and long-term consequences of deliberately tanning during peak UV hours? Does this risk vary depending on skin tone?

When you lay out during peak UV, you’re getting a blast of radiation at its strongest. On the surface you might see a tan or burn, but underneath, UV rays are breaking DNA, stressing out skin cells and weakening your skin’s immune defenses.

Short-term effects include sunburns, tans and more breakouts of things like cold sores. Over time, UV damage can lead to wrinkles, skin thinning, uneven pigmentation and increased risk of skin cancers that can be life threatening, like melanoma.

And just to be clear — no skin tone is immune. Darker skin tones don’t burn as easily, but UV damage still builds up and can lead to hyperpigmentation or skin cancers that are often diagnosed later because people don’t expect them.

Some people believe a “base tan” or tanning in short bursts is safer. Are there any tanning myths or misconceptions you wish more people understood?

One of the biggest myths is that a “base tan” protects you. The truth is, a tan is your skin’s response to damage — it translates to your cells pumping out melanin, the protein that makes you dark, to shield the rest of your skin cell from more injury. That tiny bit of protection is nowhere near as strong as sunscreen, and you had to damage your skin just to get it. Even the darkest natural skin tones don’t block UV completely, so no one is off the hook.

Lately, there’s been some misinformation online claiming sunscreen is harmful or unnecessary. As a dermatologist, what would you say to someone who’s questioning whether they should use sunscreen at all?

It’s easy to feel overwhelmed by all the mixed messages online. But here’s the fact: sunscreen is safe, effective, and one of the simplest ways to prevent skin cancer and premature aging.

Some myths I’ve heard on social media:

• Sunscreen is toxic and harmful: Some studies in mice found signs of malignant transformation when animals were exposed to very high doses of certain ingredients in chemical sunscreens under conditions that don’t reflect typical human use. Those results don’t translate to everyday, real-world applications on people. If you want to minimize any of those risks, mineral sunscreens (zinc oxide, titanium dioxide) are great alternatives.
• Sunscreen is bad for the environment: Not all sunscreens have a negative impact on coral reefs. Only certain chemical blockers such as oxybenzone and octinoxate have been found to be associated with coral bleaching. If you want to be more conscientious about the environment but still stay protected, look for mineral sunscreens or “reef-safe” options.
• Sunscreen will cause vitamin D deficiency: The truth is, the sun is a really unreliable way to get vitamin D because it varies by season, skin tone and geography — and the UV damage outweighs the benefits. A vitamin D supplement is a safer, more consistent choice.

I hear this often from my older patients with skin cancers: “I wish I had worn more sunscreen when I was younger.” Right now, you have tons of options — lotions, sprays, gels, sticks, even tinted sunscreens that blend well with different skin tones. There’s truly something for everyone. So if you’re debating sunscreen, remember: it’s not about fear, it’s about future-proofing your skin. Protect it now, and your older self will thank you.

For those who want to enjoy sunny days without harming their skin, what are your best strategies — especially beyond the usual “wear sunscreen and a hat”? Are there any lesser-known habits or routines that make a real difference long-term?

You don’t have to avoid the sun completely, just be smart about it:

• Stay in shaded areas when possible and try to do outdoor activities before 9 a.m. or after 4 p.m., when the UV index is lower.
• Check the UV index on your phone. If the UV index is greater than 3, you should have some form of sun protection. Don’t let clouds fool you: UV radiation is still present on overcast days and cuts through the clouds.
• The bread and butter of “wear sunscreen and a hat” is still important. Go for broad-spectrum SPF 30 or higher. Use a quarter of a teaspoon for the face (two finger lengths is a great hack), and a shot-glass amount for the body. Reapply every 90 minutes and set a phone alarm to remind yourself!
• There are many fun, stylish options for photo-protective clothing, hats and sunglasses. You should choose UPF 30+ shirts, wide-brim hats that cover the ears and neck, and sunglasses to protect your eyes. If you don’t want to buy new clothes, there’s even a laundry additive called SunGuard that adds UV protection to what you already own.
• There is a fern-derived dietary supplement, polypodium leucotomos, that offers some added protection, but it’s only a backup, never a replacement for sunscreen and shade.
  
  Source: UC San Diego