Should We Use Sunscreen 365 Days a Year? SPF Guide
"80% of sun damage comes from daily exposure – not a few hours spent on the beach. That's why sunscreen should be a part of your morning routine, not just your summer routine."
– Pharmacist Berfin Işık, Pharmacist and Skincare Specialist
Sunscreen is the most fundamental skincare product, protecting the skin against UVA and UVB rays and providing daily photoprotection. Regarded by dermatologists as the most effective and proven method for anti-aging protection, sunscreen should be used not only on the beach but every day and in every season. So, what is UV radiation, how does it damage the skin, and how do you choose the right sunscreen? In this comprehensive guide, we will progressively break down scientifically based information.
Why Should You Use Sunscreen 365 Days a Year?
Sun protection is necessary not only in summer but also in winter. UV rays reach your skin even on cloudy days, and even through fog and rain. Research shows that 80% of sun damage comes from daily exposure. Hours spent by a window in the office or walking down the street can cause serious skin damage, not just a few hours spent on the beach.
Although UV intensity is lower in winter, it still poses a significant threat to anyone spending time outdoors. In addition, the reflective properties of snow surfaces can multiply the UV effect — as white surfaces reflect sunlight, your skin is exposed to UV radiation twice. When makeup, frequent cleansing, incorrect product use, and certain invasive procedures weaken the skin's protective barrier, the risk of UV damage further increases.
What is UV Radiation? (UVA vs UVB Difference)
Sunlight is a type of electromagnetic radiation that reaches Earth's atmosphere. UV (ultraviolet) rays are invisible rays with wavelengths between 100–400 nm. These rays are divided into two main types:
- UVB (280–320 nm): Absorbs energy in the surface layer of the skin (epidermis). It causes sunburn, DNA damage, and cell death by forming thymine dimers in DNA. UVB is the primary cause of non-melanoma skin cancers and directly triggers DNA strand breaks.
- UVA (320–400 nm): Penetrates deeper and creates free radical oxygen species (ROS) that break down collagen and elastin fibers in the dermis. UVA increases the risk of premature aging, spots, and melanoma. Although it indirectly damages DNA, its effects are more destructive in the long term.
Simply put: UVB causes short-term damage by burning the skin's surface, while UVA penetrates deep into the skin, increasing the risk of aging and cancer. Both are harmful, and effective sunscreen should provide protection against both types of radiation.
Effects of Sun Damage on the Skin
| Effect | Description |
|---|---|
| Photoaging (Premature Aging) | UVA rays activate matrix metalloproteinase (MMP) enzymes that break down collagen and elastin. Skin elasticity decreases, and fine lines and wrinkles appear. Photoaging can progress much faster than chronological aging. |
| Hyperpigmentation (Spots) |
UV damage stimulates melanocyte cells to produce excessive melanin. Dark spots on freckles, sunspots (solar lentigo), and post-inflammatory hyperpigmentation occur. |
| DNA Damage and Cancer Risk | UVB forms thymine dimers in the skin's DNA. If the cell's repair mechanisms are insufficient, it leads to mutations and the risk of melanoma and basal cell cancer. UVA also indirectly damages DNA with free radicals. |
| Collagen Breakdown and Wrinkles | Proteinase enzymes break down the structural proteins of the dermis. Skin health and elasticity are lost, wrinkles deepen, and skin thickness decreases. |
| Increased TEWL and Dryness | UV damage weakens the stratum corneum (corneal layer) and the dermoepidermal barrier. Water loss (TEWL) increases, skin dryness intensifies, and irritation occurs, especially in sensitive skin. |
| Chronic Inflammation | Chronic UV exposure makes skin inflammation constant. Symptoms such as rosacea, acne, and eczema worsen, and cytokine production increases, accelerating aging. |
What Do SPF, PA, and Broad Spectrum Mean?
SPF (Sun Protection Factor): Indicates the level of protection against UVB radiation. SPF 30 means it provides 30 times longer protection compared to the time it takes for your unprotected skin to get sunburned. However, this is not an absolute time — it depends on skin type, UV index, sun intensity, correct application amount, and frequency of reapplication. According to the FDA, SPF 15 or higher protection is recommended.
PA (Protection Grade of UVA): Indicates the level of UVA radiation blocking. It is graded according to the Japanese standard:
- PA+: ~1/4 of UVA is filtered (minimal protection)
- PA++: ~1/2 of UVA is filtered (moderate protection)
- PA+++: ~3/4 of UVA is filtered (high protection)
- PA++++: More than 90% of UVA is filtered (maximal protection)
Broad Spectrum: Refers to products that provide protection against both UVB and UVA. Research has shown that a product lacking a UVB filter provides immunosuppression, while a broad-spectrum product with the same SPF provides significantly more protection.
Recommended Choice: For daily use, SPF 30–50; for outdoor activities or the beach, SPF 50+. UVA protection should always be at PA++ or PA+++ level, preferably broad-spectrum products.
Comparison of Chemical vs. Physical Filters
| Feature | Chemical Filter | Physical (Mineral) Filter |
|---|---|---|
| Mechanism of Action | Absorbs UV rays, converts them to heat | Reflects and scatters UV rays (reflection/scattering) |
| Onset of Action | 15–20 minutes (needs to be absorbed by the skin) | Immediate (protection starts after application) |
| Texture and Appearance | Light, homogenous, "invisible" layer on the skin | Thicker, can leave a white cast |
| Skin Penetration | Yes, can penetrate the dermis (systemic absorption) | No, stays on the skin's surface (minimal absorption) |
| Irritation Risk | Can cause irritation in sensitive skin (avobenzone, octinoxate) | Generally well tolerated, hypoallergenic |
| Water Resistance | Variable (depends on formulation) | Generally more resistant |
|
Ingredients |
New and old generation chemical filters | Titanium dioxide, zinc oxide |
| Suitable Skin Types | Normal, oily, combination skin | All skin types, especially sensitive, reactive, rosacea, eczema, children, pregnant women |
| Price | Generally more affordable | More expensive |
| Advantages | Light texture, homogeneous appearance, low comedogenic score | Immediately effective, stable formulation, minimal systemic absorption, hypoallergenic, safe profile |
| Disadvantages | Potential irritation, systemic absorption | Leaves white cast, thicker texture, feeling of a layer |
Hybrid Formulas (Combination): Products containing both chemical and physical filters provide broad-spectrum protection while having a lighter texture. They are an ideal choice for most skin types — offering superior technology and tolerance combined.
How to Choose the Right Sunscreen?
When choosing sunscreen, consider the following criteria:
- SPF Value: Minimum SPF 30 for daily use, SPF 50+ for outdoor activities
- UVA Protection: PA++ or PA+++ is minimally recommended
- Broad Spectrum: The product label should state "Broad Spectrum"
- Filter Type: If sensitive skin, choose physical/mineral filter; if normal skin, prefer a hybrid formula
- Texture: For face, serum or gel-cream; for body, thicker formulas can be chosen
- Water Resistance: If you expect swimming or sweating, choose a water-resistant product
- Skin Type Compatibility: Prefer hybrid formulations that contain new-generation chemical filters combined with physical filters, which are non-comedogenic (pore-blocking) and have low irritant potential
How and How Much to Apply?
Application Amount
At least 1/4 teaspoon (approximately 0.5 ml) of sunscreen should be used for the face and neck. Dermatological tests show that this amount is needed to achieve the effective SPF value. Most people apply an insufficient amount, which results in weak protection — this is the most common sunscreen application mistake.
Application Order
For a daytime skincare routine with a UV index of 2 or higher, the following order is recommended:
- Cleansing
- Toner/Essence (if any)
- Serum (if any)
- Day Cream / Moisturizer
- Sunscreen (last step, continue with makeup after 15 minutes)
Reapplication
Sunscreen should be reapplied after water activities, sweating, or at the latest every 2-3 hours even without these factors. If it's difficult to apply over makeup, you can opt for sunscreen spray or compact products containing sun filters for reapplication.
Year-Round Routine
- Summer (May-October): SPF 50+, PA+++ or PA++++, reapply every 2 hours, and if you sweat a lot, choose water and sweat-resistant products daily
- Late Spring / Early Autumn: SPF 40-50, PA++, reapply every 3 hours
- Winter (November-April): SPF 30–50, PA++, daily morning application is sufficient (reapplication critical during outdoor activities)
- Cloudy days: Minimum SPF 30, SPF 50 can be chosen depending on the UV index
- In the Office/Indoor: SPF 30 is sufficient; those exposed to natural light (by a window) should prefer SPF 50
Light Through Glass and Sunscreen Use at Home
"I'm at home, I don't need sunscreen" is a common misconception. This is because some of the light hitting the glass continues to reach the skin. Standard window glass blocks about 99% of UVB rays; however, it allows 50–75% of UVA rays to pass through. UVA penetrates deep into the dermis, leading to collagen breakdown, photoaging, and stubborn spots like melasma. Therefore, hours spent by a window, in a car, or on a glass balcony cause silent and cumulative damage to the skin.
UVA is not the only type of light that passes through glass. High-energy visible light, also known as blue light (HEV), and infrared (IR-A) also pass through glass. Blue light from screens and LED lighting has been shown to trigger pigmentation, especially in darker skin types. The table below summarizes which types of light pass through glass:
| Light Type | Wavelength | Passes Through Glass? | Effect on Skin |
|---|---|---|---|
| UVB | 280–315 nm | No (≈99% blocked) | Superficial burn, DNA damage |
| UVA | 315–400 nm | Largely yes | Collagen breakdown, photoaging, spots |
| Blue Light (HEV) | 400–500 nm | Yes | Pigmentation, oxidative stress |
| Infrared (IR-A) | >700 nm | Yes | Free radical production |
The difference with time spent at home is this: outdoors, there is broad-spectrum and intense UV exposure, while indoors, exposure is lower but continuous. For those working by a window, using a glass balcony, or spending the day in front of a screen, applying a broad-spectrum (UVA + UVB) sunscreen, preferably with blue light protection, in the morning provides significant protection even at home. Mineral filter or tinted formulas containing iron oxide are particularly suitable for indoor use as they offer an additional barrier against visible and blue light.
Sunscreen at Medicblu
Medicblu offers many sunscreen alternatives formulated with physical, chemical, and hybrid filters. You can easily find the right sunscreen for you by using the filtering options or get support from our experts via our corporate 850 line using the 'Consult an Expert' option.
Frequently Asked Questions (FAQ)
Q: Should sunscreen be applied every day?
A: Yes. No matter the weather, season, or your plans, you should use sunscreen if you're going outside. UV rays reach our world every day of the year and cause cumulative damage.
Q: Is sunscreen necessary in cloudy weather too?
A: Generally, SPF 30 is sufficient indoors. However, if you are working by a window or near an open window, opt for SPF 50. Glass blocks 99% of UVB but lets through 75-90% of UVA.
Q: Is SPF 30 enough, or SPF 50?
A: SPF 30 may be sufficient for daily use, but research shows that those using SPF 50 have a lower risk of cancer. For outdoor activities, the beach, or prolonged UV exposure, choose SPF 50+.
Q: Is sunscreen used with retinol?
A: Yes, it is important to use it. Retinol increases the skin's UV sensitivity, so those using retinol should use high SPF (50+) sunscreen. Use SPF 50 in your morning routine and retinol in your night routine.
Q: How often should sunscreen be reapplied?
A: Immediately after water activity or heavy sweating. For direct skin exposure, every 2 hours; for winter months or indoor use, once in the morning is sufficient. If you stay in the office all day, reapplication every 2 hours is not necessary.
Q: If my face cream contains SPF, do I need additional sunscreen?
A: Usually, yes. The SPF in face creams is low (generally SPF 15-25) and the application amount is often insufficient. For effective protection, it is recommended to use a dedicated sunscreen with SPF 30+.
Conclusion
Sunscreen is the most effective and proven method of protection against aging. Photoaging, pigmentation, DNA damage, and cancer risk caused by UVA and UVB radiation on the skin can only be prevented with regular sun protection. Choose products with SPF 30–50 and PA++ or higher, preferably with a hybrid formula, incorporate it into your morning routine as a strict habit, and reapply every 2 hours.
Sun protection is not a decision made today, but a lifelong habit. The investment you make in your skin in your 20s and 30s will be the most valuable gift in your 50s and 60s.
Scientific References
- Lim HW, Arellano-Mendoza MI, Stengel F. Sunscreens and Photoprotection. StatPearls. NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK537164/
- Sunscreens Part 1: Mechanisms and Efficacy (2024). J Am Acad Dermatol. https://www.jaad.org/article/S0190-9622(24)00785-0/abstract
- Lawrence KP et al. Improved photoprotection in the UVA/visible radiation boundary region is essential to prevent DNA damage, oxidative stress and gene expression changes in human skin. JEADV Clin Pract. 2025. https://doi.org/10.1002/jvc2.586
- Moyal DD, Fourtanier AM. Broad-spectrum sunscreens provide better protection from solar ultraviolet-simulated radiation and natural sunlight-induced immunosuppression in human beings. J Am Acad Dermatol. 2008;58(5 Suppl 2):S149-54. PMID: 18410801
- Guan LL, Lim HW, Mohammad TF. Sunscreens and Photoaging: A Review of Current Literature. Am J Clin Dermatol. 2021;22(6):819-828. PMID: 34387824
- Cayrol C et al. A mineral sunscreen affords genomic protection against ultraviolet (UV) B and UVA radiation: in vitro and in situ assays. Br J Dermatol. 1999;141(2):250-8. PMID: 10468796
- Brar G et al. A Comprehensive Review of the Role of UV Radiation in Photoaging Processes Between Different Types of Skin. Cureus. 2025;17(3):e81109. PMID: 40276407
- Coelho SG et al. Suboptimal UVA attenuation by broad spectrum sunscreens under outdoor solar conditions contributes to lifetime UVA burden. Photodermatol Photoimmunol Photomed. 2019;36(1):42-52. PMID: 31376300
