SPF Explained: The Science of Sun Protection and How to Support Healthy Skin From the Inside Out
Key Takeaways
- SPF is one of the most important daily tools for reducing UV-related skin damage, but it works best as part of a broader skin-supportive lifestyle.
- UVA rays are closely linked with photoageing, while UVB rays are more strongly associated with sunburn and direct DNA damage.
- Antioxidant-rich foods, hydration, sleep, and gut health may help support the skin’s resilience against oxidative stress.
- Nutrition can complement sun protection, but it does not replace a broad-spectrum sunscreen.
- Consistent habits matter more than chasing the “perfect” sunscreen or the highest SPF number.
- Not all SPF products are created equal, so see our health hacks to choose the best types
- Spend time outdoors in the early morning to support your body's natural circadian rhythm, vitamin D, and overall wellbeing, while avoiding excessive midday UV exposure
On bright summer days, I often remind patients that skin health is rarely about one heroic product. It’s usually the quiet, everyday things that shape resilience over time.
Sunny days invite us outdoors, whether it’s a beach holiday, a walk with the dog, time in the garden, or simply lunch outside. Moderate sun exposure does have health benefits, including support for vitamin D production and circadian rhythms, but too much ultraviolet radiation can accelerate visible skin ageing and increase the risk of skin cancer.¹
Sunscreen is one of the most effective tools we have to reduce UV-related damage. But healthy skin doesn’t depend on sunscreen alone.
What we eat, how well we sleep, how hydrated we are, how our gut is functioning, and how well we’re handling oxidative stress all play a part in how resilient our skin may be. So rather than seeing sunscreen as the whole answer, I think it’s more useful to see it as one important layer in a broader approach to skin health.
In this guide, I’ll walk you through how UV radiation affects the skin, how SPF works, how to choose the right sunscreen, and how to support healthy skin from the inside out.
Why SPF Matters
Your skin is exposed to sunlight every day, often in ways you barely notice. And while visible sunburn gets our attention, UV-related changes can begin beneath the surface long before you see them.¹
Repeated UV exposure can contribute to:
- Premature skin ageing
- Pigmentation
- Wrinkles
- Reduced collagen production
- DNA damage
- Increased oxidative stress
- A greater risk of skin cancers
The encouraging part? Much of this damage is cumulative, which means consistent daily protection can make a real difference over time.¹
What Happens to Your Skin in the Sun?
When patients understand what sunlight is actually doing in the skin, sunscreen starts to make a lot more sense. And so do all the “inside-out” habits that support recovery.
UVA Rays: The Ageing Rays
UVA rays make up most of the ultraviolet radiation that reaches the Earth’s surface. They penetrate more deeply into the dermis, where collagen and elastin help keep skin firm and supple.¹
Over time, UVA exposure is associated with:
- Fine lines
- Wrinkles
- Loss of elasticity
- Hyperpigmentation
- Oxidative stress
Because UVA can pass through clouds and glass, exposure can still happen while driving or sitting near a sunny window. It’s one reason daily protection matters more than many people realise.¹⁵
UVB Rays: The Burning Rays
UVB rays carry more energy and primarily affect the outer layers of the skin. They’re most strongly associated with sunburn, direct DNA damage, inflammation, and an increased risk of skin cancer.¹⁵
UVB intensity is usually greatest in the middle of the day, and it varies with season, altitude, and location. That’s worth keeping in mind in places with strong summer sun.
Oxidative Stress And Free Radicals
One of the biggest downstream effects of UV exposure is oxidative stress. In simple terms, that means the body is producing more reactive molecules—often called free radicals—than it can comfortably neutralise.²
These unstable molecules can damage:
- Cell membranes
- Proteins
- DNA
- Mitochondria
When that load outweighs the body’s antioxidant defences, oxidative stress may contribute to inflammation and faster skin ageing.²
Collagen Breakdown
Collagen gives skin much of its strength and structure. UV exposure activates enzymes called matrix metalloproteinases, or MMPs, which break down collagen fibres and disrupt the skin’s support network.¹ ³
Over time, this can contribute to:
- Wrinkles
- Thinner skin
- Reduced firmness
- Slower repair
This is one reason protecting collagen matters so much in any healthy-ageing conversation. It’s not vanity. It’s biology.
Mitochondrial Damage
Mitochondria are the energy-producing parts of the cell. Emerging research suggests UV radiation may impair mitochondrial function, which can increase oxidative stress and reduce how efficiently the skin repairs itself.⁴
We still have more to learn here, but it fits with what I often see in clinic: skin tends to do better when the whole system is better supported.
How Does SPF Work?
SPF stands for Sun Protection Factor. It measures protection primarily against UVB rays rather than the full picture of UVA exposure, which is why broad-spectrum labelling matters.¹² ¹³
As a rough guide:
- SPF 15 filters about 93% of UVB rays
- SPF 30 filters about 97%
- SPF 50 filters about 98%
No sunscreen blocks 100% of UV radiation. And the jump between SPF 30 and SPF 50 is smaller than many people think, so generous application and regular reapplication usually matter more than fixating on the highest number on the bottle.¹² ¹³
Mineral Vs Chemical Sunscreens
This is one of those topics that can become needlessly polarised online. In reality, both mineral and chemical sunscreens can be effective when they’re well formulated and used correctly.
Mineral Sunscreens
Mineral sunscreens usually contain:
- Zinc oxide - a good and safe choice
- Titanium dioxide - best to avoid due to links to DNA damage and immune system toxicity
Zinc oxide works by reflecting and absorbing UV radiation, and many people with more reactive or sensitive skin prefer them. Personally, I recommend a mineral sunscreen over high street SPF versions due to the many added unnecessary chemicals that may interfere with normal detox pathways.
How To Choose The Right SPF
Look for:
- Broad-spectrum protection (UVA + UVB)
- SPF 30–50 (I prefer the 30s, as you can usually find great zinc oxide options with fewer chemicals and excellent protection)
- Water resistance if you’re swimming or exercising
- A formula suited to your skin type and routine
And don’t forget the basics:
- Apply it generously.
- Reapply every two hours outdoors.
- Reapply after swimming or heavy sweating.
- Cover easy-to-miss areas like the ears, neck, hands, and feet.
- Opt for shade when possible and avoid peak times of 11–2 pm with constant direct sun.
No sunscreen lasts all day. I know that’s not the most glamorous message, but it’s the honest one.¹⁴ ¹⁶
Can Food Help Protect Your Skin?
Nutrition cannot replace sunscreen. But certain nutrients may help support the skin’s own antioxidant networks and resilience against UV-related oxidative stress.⁴ ⁵
I often frame this as “supportive photoprotection.” Helpful? Yes. A substitute for SPF? No.
Lycopene
Lycopene is a carotenoid found in tomatoes, watermelon, and pink grapefruit. Some evidence suggests regular intake may help reduce UV-induced skin redness and support the skin’s natural defence systems over time.⁵ ⁶
Cooked tomatoes are especially useful here because heating improves lycopene availability.
Astaxanthin
Astaxanthin is a potent antioxidant found naturally in salmon, trout, and microalgae. Research suggests it may help support skin hydration, elasticity, and resilience against oxidative stress.⁷ In fact, this ingredient is such a powerhouse it is a hero ingredient in our new Rejuv Age Well capsules.
Vitamin C
Vitamin C is essential for collagen synthesis and also helps regenerate other antioxidants, including vitamin E. It plays an important role in maintaining skin structure and antioxidant protection.⁸ Plant-based vitamin C is often preferred over ascorbic acid, but getting enough before a day in the sun can be tricky. To fast track this, I take our Rejuv Immune Support capsules, and the highly bioavailable vitamin C is also helpful if you choose to swim in a chlorinated pool.
Good sources include:
- Citrus fruit
- Kiwi
- Capsicum
- Strawberries
- Broccoli
- Berries
Vitamin E
Vitamin E helps protect cell membranes from oxidative damage and works particularly well alongside vitamin C.⁹
Food sources include:
- Almonds
- Sunflower seeds
- Avocado
- Olive oil
- Vitamin E is also a key ingredient of our Age Well capsules above
Carotenoids
Carotenoids such as beta-carotene, lutein, and zeaxanthin are colourful plant compounds that can accumulate in the skin and may contribute to natural photoprotection over time.⁵
Polyphenols
Polyphenols are plant compounds found in foods such as green tea, berries, cocoa, olive oil, and grapes. Some research suggests they may help moderate inflammation and oxidative stress linked with UV exposure.¹¹
Omega-3 Fats
Omega-3 fats support healthy cell membranes and may help regulate inflammatory responses following UV exposure.¹⁴
Useful sources include:
- Oily fish
- Walnuts
- Chia seeds
- Flaxseed
The Gut–Skin Axis
Your gut and skin are more connected than many people realise. The gut microbiome helps regulate immune activity, inflammation, nutrient absorption, and aspects of skin barrier function.¹⁰
When the gut microbiome is out of balance, systemic inflammation may rise, which can influence how resilient the skin feels and behaves. This is the gut–skin axis in action: a two-way conversation between digestive health, immunity, and the skin.¹⁰
That’s why I so often come back to basics like fibre diversity, hydration, and whole foods. Sometimes the skin conversation really begins in the gut.
Cloudy apple cider vinegar is brilliant for supporting your gut–skin axis. You can dilute 1 tbsp in water and drink before meals, or if you're concerned about tooth enamel, you can take Apple Cider capsules instead.
Why Antioxidants Matter After Sun Exposure
Even with sunscreen, some UV-related oxidative stress still occurs. Antioxidants help neutralise excess free radicals and support the body’s natural repair processes.² ⁴
That doesn’t make them a replacement for SPF. It makes them a useful partner.
The strongest approach usually combines:
- Daily SPF
- Antioxidant-rich foods
- Good hydration
- Quality sleep
- Regular movement
- Healthy gut function
- Bioavailable supplementation of plant-based vitamin C and antioxidants such as in our Antioxidant Complex
Healthy skin tends to respond best to consistency, not intensity.
10 Science-Backed Ways To Support Healthy Skin This Summer
- Wear a broad-spectrum mineral-based SPF 30 every day.
- Reapply sunscreen every two hours when outdoors.
- Wear a wide-brimmed hat that covers your full face and neck.
- Seek shade during peak UV hours.
- Eat colourful fruit and vegetables daily.
- Include healthy fats such as olive oil and oily fish.
- Stay well hydrated.
- Prioritise sleep to support overnight skin repair.
- Support gut health with fibre-rich foods and fermented foods where appropriate.
- Implement a Skin Stack System to support your skin from within: My personal stack includes our Age Well Capsules, Antioxidant Complex and Apple Cider Burn capsules. If I am to swim in a chlorinated pool or attend a water park with my kids, I load us all up on plant-based vitamin C with our Immune Support capsules.
Five Common SPF Myths
Myth 1: SPF 50 Gives Twice The Protection Of SPF 25
Not quite. SPF 50 blocks only slightly more UVB than SPF 30, which is why how you apply and reapply matters far more than many people think.¹² ¹³
Myth 2: You Don’t Need Sunscreen On Cloudy Days
False. UV radiation can still penetrate cloud cover, and UVA exposure remains relevant even when the day doesn’t feel particularly sunny.¹⁵
Myth 3: Darker Skin Doesn’t Need SPF
False. Melanin does offer some natural protection, but all skin tones can experience UV damage, pigmentation changes, and skin cancer.¹⁵
Myth 4: One Morning Application Lasts All Day
False. Sweating, swimming, friction, and ordinary daily movement all reduce sunscreen effectiveness, so regular reapplication is essential.¹⁴ ¹⁶
Myth 5: Natural Oils Replace Sunscreen
False. Although some plant oils contain naturally occurring UV-filtering compounds, they do not provide reliable, tested, broad-spectrum protection.
Frequently Asked Questions
Can nutrition replace sunscreen?
No. A nutrient-rich diet may support the skin, but it cannot prevent UV damage on its own.⁴ ⁵
Is SPF needed indoors?
If you spend time near large windows or drive frequently, UVA exposure can still occur. In that case, daily SPF is often worth considering.¹⁵ Plus, don’t forget to protect your hands if driving frequently.
Is higher SPF always better?
For most people, SPF 30 offers excellent protection when applied properly and reapplied consistently.¹² ¹³
Does sunscreen stop vitamin D production?
Research suggests normal sunscreen use does not usually prevent adequate vitamin D production in everyday life. It’s a more nuanced relationship than many headlines suggest.
The Rejuv Take
Healthy skin is built through steady daily habits, not one miracle product. Sunscreen remains one of the most effective ways to protect your skin from ultraviolet damage, but it works best as part of a wider, whole-body approach.¹² ¹⁵
A colourful, nutrient-rich diet, good hydration, restorative sleep, regular movement, healthy gut function, and antioxidant support may all help strengthen the skin’s natural defence and recovery processes.⁴ ⁹ ¹⁰ ¹¹
If you’re already thinking about cellular health, oxidative stress, or subtle antioxidant support, this is exactly where those conversations fit. Not as hype. As foundations.
Rather than choosing between sunscreen and nutrition, think of them as partners. Protect your skin from the outside while nourishing it from the inside.
That’s the Rejuv approach to healthy ageing: supporting resilience, not chasing perfection.
If this has prompted you to think more broadly about your skin, energy, stress load, or overall resilience, take a few quiet minutes to reflect on the bigger picture. You can also complete the Wellness Profile for a more personalised starting point.
References
- Fisher GJ, Kang S, Varani J, Bata-Csorgo Z, Wan Y, Datta S, Voorhees JJ. Mechanisms of photoaging and chronological skin aging. Archives of Dermatology. 2002;138(11):1462-1470. https://pubmed.ncbi.nlm.nih.gov/12437452/
- Krutmann J. Skin ageing and oxidative stress. Experimental Dermatology. 2001;10(5):303-304. https://pubmed.ncbi.nlm.nih.gov/?term=Krutmann+skin+ageing+and+oxidative+stress
- Rittié L, Fisher GJ. UV-light-induced signal cascades and skin aging. Ageing Research Reviews. 2002;1(4):705-720. https://pubmed.ncbi.nlm.nih.gov/12208239/
- Schagen SK. Topical and nutritional antioxidants in skin health. Journal of Drugs in Dermatology. 2017;16(4):s107-s111. https://pubmed.ncbi.nlm.nih.gov/?term=Schagen+topical+and+nutritional+antioxidants+in+skin+health
- Stahl W, Sies H. Carotenoids and flavonoids contribute to nutritional protection against skin damage from sunlight. Molecular Biotechnology. 2007;37(1):26-30. https://pubmed.ncbi.nlm.nih.gov/?term=Stahl+Sies+carotenoids+photoprotection+skin
- Rizwan M, Rodriguez-Blanco I, Harbottle A, Birch-Machin MA, Watson REB, Rhodes LE. Tomato paste rich in lycopene protects against cutaneous photodamage in humans in vivo. British Journal of Dermatology. 2011;164(1):154-162. https://pubmed.ncbi.nlm.nih.gov/?term=Rizwan+tomato+lycopene+photodamage+humans+in+vivo
- Tominaga K, Hongo N, Karato M, Yamashita E. Cosmetic benefits of astaxanthin on humans subjects. Acta Biochimica Polonica. 2012;59(1):43-47. https://pubmed.ncbi.nlm.nih.gov/?term=Tominaga+astaxanthin+skin+health
- Pullar JM, Carr AC, Vissers MCM. The roles of vitamin C in skin health. Nutrients. 2017;9(8):866. https://pubmed.ncbi.nlm.nih.gov/?term=Pullar+Carr+Vissers+roles+of+vitamin+C+in+skin+health
- Thiele JJ, Ekanayake-Mudiyanselage S. Vitamin E in human skin: Organ-specific physiology and considerations for its use in dermatology. Molecular Aspects of Medicine. 2007;28(5-6):646-667. https://pubmed.ncbi.nlm.nih.gov/?term=Thiele+Vitamin+E+human+skin
- Del Rosso JQ. The role of the skin microbiome and the gut-skin axis in inflammatory skin conditions. Journal of Clinical and Aesthetic Dermatology. 2018;11(2):36-41. https://pubmed.ncbi.nlm.nih.gov/?term=Del+Rosso+gut+skin+connection
- Nichols JA, Katiyar SK. Skin photoprotection by natural polyphenols: anti-inflammatory, antioxidant and DNA repair mechanisms. Archives of Dermatological Research. 2010;302(2):71-83. https://pubmed.ncbi.nlm.nih.gov/?term=Nichols+Katiyar+skin+photoprotection+polyphenols
- Wang SQ, Balagula Y, Osterwalder U. Photoprotection: a review of the current and future technologies. Dermatologic Therapy. 2010;23(1):31-47. https://pubmed.ncbi.nlm.nih.gov/?term=Wang+Balagula+Osterwalder+photoprotection+review
- Young AR. Sunscreens and their use in the prevention of actinic damage. Photodermatology, Photoimmunology & Photomedicine. 2001;17(6):253-257. https://pubmed.ncbi.nlm.nih.gov/?term=Young+AR+sunscreens+prevention+skin+damage
- Calder PC. Omega-3 fatty acids and inflammatory processes: from molecules to man. Biochemical Society Transactions. 2017;45(5):1105-1115. https://pubmed.ncbi.nlm.nih.gov/?term=Calder+omega-3+fatty+acids+inflammatory+processes
- World Health Organization. Ultraviolet radiation. World Health Organization; updated 2022. https://www.who.int/news-room/fact-sheets/detail/ultraviolet-radiation
- World Health Organization. Global solar UV index: a practical guide. World Health Organization; 2002. https://www.who.int/publications/i/item/9241590076
