Conscious sun exposure and skin protection. When does SPF help?
Before reaching for the sunscreen, it’s worth asking yourself: when and why am I using it? In recent years, sun protection has gained huge popularity. At the same time, more and more people are seeking a more balanced approach - one that combines care for the skin with the benefits of light exposure.
In this article, we take a closer look at what SPF is and when it’s worth using.
What is SPF and how does it work?
SPF (Sun Protection Factor) is a measure of how well a sunscreen protects the skin against UVB radiation—the kind responsible for sunburn, redness, and some forms of skin cancer. In practice, SPF indicates how many times longer protected skin can be exposed before reddening, compared to unprotected skin.
- SPF 15 blocks approx. 93% of UVB
- SPF 30 blocks approx. 97% of UVB
- SPF 50 blocks approx. 98% of UVB
- SPF 100 blocks approx. 99% of UVB
The differences may seem small, but during long or intense exposure, they make a significant impact.
Importantly, SPF does not increase linearly! SPF 30 does not protect twice as well as SPF 15. The difference in UVB absorption is just a few %, though meaningful with prolonged exposure.
How is SPF tested?
SPF is determined through laboratory tests where volunteers’ skin is exposed to UV radiation.
The primary measurement is the Minimal Erythemal Dose (MED)—the amount of UV needed to produce barely perceptible skin redness (erythema).
Where did SPF come from? A brief history
The SPF index was developed by Austrian chemist Franz Greiter in 1962. He proposed a scientific method for expressing sunscreen effectiveness, later standardised in testing protocols such as ISO 24444 (EU) and FDA regulations (USA).
How Did Our Ancestors Protect Themselves?
Before sunscreens were invented, people protected themselves from the sun with:
- body-covering clothing – long, light fabrics in bright colours,
- headwear – scarves, turbans, wide-brimmed hats,
- natural protective substances: clays, plant oils, sandalwood paste,
- daily rhythm – avoiding the midday sun, resting in shade,
- seasonal adaptation – gradually getting the skin used to sunlight.
This traditional approach reminds us that balanced sun exposure can be a natural part of life.
Natural Vitamin D from the sun: When to use SPF
You don’t always need sunscreen. According to experts like Dr. Michael Holick, you should first allow the skin to naturally produce vitamin D, and only afterwards apply sun protection. It’s recommended to expose larger body areas (like legs and arms) without SPF, in moderation and without burning. Areas like the face, ears, or hands may be protected earlier.
Studies (e.g., Neale et al.) show that for people at low risk of skin cancer, protection is not necessary during short exposures, even when the UV Index exceeds 3. Still, protection is advised for longer sun exposure or very fair skin types.
How to apply SPF correctly?
To get the declared level of protection:
- apply approx. 2 mg/cm² of skin,
- reapply every 2 hours, and after swimming, sweating, or towel drying.
It’s best to consult a dermatologist about what SPF to choose and which brands are best for your skin. A high-quality sunscreen is a worthwhile investment.
SPF and tanning beds
In the case of tanning beds, exposure is short and tailored to your skin phototype, so using SPF for the whole body is not practically justified. Instead, professional indoor tanning cosmetics are used.
An exception is made for sensitive skin areas, which are worth protecting with, for instance, SPF 50+ sticks:
- moles and freckles,
- tattoos,
- scars and pigmentation spots,
- lips.
Light with awareness: When does skin need support?
Moderate sun exposure — without filters — supports vitamin D synthesis, circadian rhythm, and overall well-being. Use SPF when:
- you plan longer sun exposure – check the UV Index beforehand,
- you have a fair phototype (check it here: Fitzpatrick scale),
- you don’t have access to physical protection.
Especially sensitive areas:
- ears, nose, neck,
- shoulders, shoulder blades, décolleté,
- lips, scalp,
- backs of hands and feet,
- tattoos, skin lesions.
Alternative protection:
- clothing with UPF (Ultraviolet Protection Factor) 30–50+,
- wide-brimmed hat,
- UV umbrella or shade.
It’s not the filter that creates safety, but awareness. Sunscreen is a supportive tool, useful when needed, but not a replacement for conscious, informed sun habits. At Sunforlife, we encourage balance: enjoy the benefits of sunlight when possible, and use sunscreen mindfully during times of higher exposure, for sensitive areas, or when other forms of protection aren’t available.
Sources – Read More:
ISO 24444:2019: Cosmetics — Sun protection test methods — In vivo determination of the sun protection factor (SPF), https://www.iso.org/standard/72250.html
Drissi M, Carr E, Housewright C. Sunscreen: a brief walk through history. Proc (Bayl Univ Med Cent). 2021 Sep
Sunscreen product regulations – European Commission: https://single-market-economy.ec.europa.eu/sectors/cosmetics/cosmetic-products-specific-topics/sunscreen-products_en, https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32006H0647
Harvard Health, The science of sunscreen, 2021 https://www.health.harvard.edu/staying-healthy/the-science-of-sunscreen
CNN USA, Only one-quarter of sunscreens on store shelves are safe and effective, new report, 2025, https://edition.cnn.com/2025/05/20/health/2025-safest-sunscreens-wellness
Stanford Medicine, Sunscreen fact and fiction: What the science says, 2025: https://med.stanford.edu/news/insights/2025/06/sunscreen-science.html
GrassrootsHealth / Interview with Dr. Michael Holick, 2022 oraz opracowanie: Beyond Vitamin D Production — How Sensible Sun Exposure Supports Overall Health, Joseph Mercola, 2025
The Guardian, 2024: https://www.theguardian.com/australia-news/2024/feb/13/australias-sun-safety-guidelines-updated-to-take-account-of-diverse-skin-types?
