Do you need sunscreen all day? Here's how often you should reapply

Cloudy with no reason for sunscreen.

Don’t worry if you’ve ever thought that way—most of us have. After all, the word ‘sun’ is right there in the name, making it easy to assume sunscreen is only for sunny days or poolside lounging. But here’s the reality: sunscreen isn’t just a skincare ritual or a vacation essential—it’s your everyday shield against skin damage that can haunt you over time.

That said, sunscreen often raises some key questions: Do you really need it all day? Does that mean constant reapplication? Or is one morning layer enough to see you through? Let’s break it down.

The sunlight you can’t see

Think you’re safe indoors or under an overcast sky? Think again.

As Natasha Ray, a Dubai-based dermatologist specialist explains, “Around 80 per cent of the sun’s ultraviolet rays penetrate clouds, which means that your skin is still exposed to harmful radiation. Moreover, when it comes to office windows or even car rides, glass might block UVB rays, but UVA rays, which are the reasons behind premature aging and deep skin damage, can come right through.” As she summarises: The sun’s rays are unavoidable; so don’t be fooled on overcast days.

Ray also emphasises, applying sunscreen doesn’t just mean you’re protecting yourself from sunburn. The sun’s UVB rays also play a role in causing skin cancers. In addition, the UVA rays penetrate more deeply into the skin and play a greater role in premature skin aging changes including wrinkle formation.

In other words, UV radiation doesn’t punch out when the clock hits 5 PM. Whether it’s morning errands, your afternoon coffee run, or a sunset stroll, your skin is clocking hours of exposure.

Indoors and blue light

It's not just sunlight you need to worry about. Blue light, emitted by devices like smartphones, laptops, and indoor LED lighting, can also contribute to skin damage. Studies suggest that prolonged exposure to blue light may lead to oxidative stress, which accelerates aging and causes hyperpigmentation.  Combined with UVA rays from sunlight streaming through windows—since standard glass can allow up to 74 per cent  of UVA radiation to pass through—your skin is under constant assault, even indoors.

The science tells the ugly truth: A 2019 study published in Scientific Reports found that blue light exposure can lead to oxidative stress, which accelerates skin aging. The research demonstrated that blue light (wavelengths between 400–450 nm) increases the production of free radicals, resulting in damage to the skin, breakdown of collagen, which leads to wrinkles and sagging skin.

Another 2020 study, published in Frontiers in Dermatology highlighted the synergistic effects of UVA and visible light, including blue light, on skin damage. This research supported the idea that both types of light contribute to oxidative stress, which accelerates the aging process and leads to skin damage, such as the formation of hyperpigmentation (dark spots) and the breakdown of collagen.

That’s why dermatologists stress reapplying sunscreen every two hours—yes, even on a workday.

How often should we apply sunscreen?

Loai Gaffer Ahmed Ali, Specialist Dermatology and  cosmetology, Aster Speciality Clinic, Ajman (Rashidiya), explains, “Sunscreen should be reapplied every two hours throughout the day to maintain its effectiveness. This is important because sunscreens can degrade over time due to various factors such as sweat, water exposure, and natural wear. Even if you’re not directly in the sun, sunscreen's protective layer can break down, reducing its ability to block harmful UV rays. Reapplication ensures continued protection from both UVA and UVB radiation, which can contribute to skin aging, sunburns, and long-term skin damage.”

Elaborating on what factors affect the frequency of sunscreen application, he explains:

Sweat and water exposure can significantly shorten the longevity of sunscreen. Sweat can cause it to slide off, while water, even from swimming or heavy perspiration, can wash it away. To maintain effective protection, it’s essential to reapply sunscreen after sweating or swimming, even with water-resistant formulas.

Is there a difference in reapplication frequency for physical versus chemical sunscreens?

Physical or mineral sunscreens contain active ingredients like titanium dioxide or zinc oxide, which act as physical blockers by reflecting UV rays before they penetrate the skin. These minerals form a protective barrier on the skin’s surface, preventing harmful rays from making contact. A key benefit of physical sunscreens is their ability to block UVA rays, which can pass through windows and contribute to pigmentation and collagen breakdown. This makes them essential for daily use, even if you're staying indoors. Physical sunscreens are ideal for children, people with sensitive skin, and individuals with melasma—a condition that causes dark patches or freckle-like spots on the skin. They provide immediate protection.

In contrast, chemical sunscreens must be applied 30 minutes before sun exposure to allow the ingredients to fully bind to the skin. Rather than sitting on the skin’s surface, these sunscreens contain ingredients that absorb UV rays, preventing them from penetrating the skin.

Explaining whether there is a difference in reapplication frequency for physical and chemical sunscreens, Ali says, “Both offer broad-spectrum protection, but the reapplication frequency is generally the same for both types. However, physical sunscreens containing zinc oxide or titanium dioxide tend to sit on the skin's surface and are less likely to be absorbed, so they may be a bit more resistant to water and sweat compared to chemical sunscreens. Still, both need to be reapplied every two hours for consistent protection,” he says.