Sun and skin: UVA, UVB, sunspots, and sun protection, what you really need to know

Journal · Sun & skin

Summer is coming, sunscreens are filling the shelves, and advice is plentiful. But behind the well-oiled prevention messages lies a more nuanced reality — and one more useful to know.

The sun is not merely an enemy to be fought. It is a source of vital energy that your skin needs, provided you understand how to tame it intelligently. Here's what science really says about this relationship.

What the sun actually does to your skin

UVA and UVB: two types of radiation, two behaviors

The sun emits several types of radiation, but two directly concern us for skin health.

UVB rays account for about 5% of the UV radiation that reaches the Earth's surface. They are responsible for sunburn, vitamin D production, and the long-term risk of skin cancer. Their intensity varies with the season, time of day, and altitude. In winter in mainland France, UVB rays are almost absent. In summer at noon in direct sunlight, they reach their peak. These are what the SPF index primarily protects against.

UVA rays account for the majority of UV radiation that reaches the Earth's surface. Unlike UVB, they penetrate deeper into the dermis — where collagen, elastin, and fibroblasts are found. They don't burn. They age.

Oxidative stress: the central mechanism

To understand why the sun ages the skin, you need to understand oxidative stress.

When UV rays reach skin cells, they trigger the production of free radicals — unstable and highly reactive molecules that attack cellular structures. These free radicals damage cell DNA, degrade existing collagen, inhibit the production of new collagen, and disrupt the skin's lipid barrier.

Our body has natural antioxidant mechanisms to counteract this attack: vitamin E from vegetable oils, vitamin C from food, melatonin produced during sleep. But faced with intense and repeated sun exposure without protection, these defenses are quickly overwhelmed. This is precisely where antioxidant active ingredients in cosmetics come in, whose role is to strengthen these natural defenses where they fail.

SPF: what the index doesn't tell you

How to read an SPF index

An SPF 30 blocks approximately 97% of UVB. An SPF 50 blocks approximately 98%. An SPF 50+ blocks approximately 99%.

The difference between an SPF 30 and an SPF 50 is therefore barely 1% in terms of actual UVB protection. This figure often surprises. It doesn't mean it's useless to choose a high index — but it puts the obsession with very high SPFs into perspective. What matters more than the index itself is the quality of UVA protection, which is not always clearly indicated on packaging, and especially how you apply your product.

The mistake everyone makes

Most people apply far too little sunscreen. SPF indices are calculated based on a dose of 2 mg per square centimeter of skin. In practice, the majority of consumers apply two to four times less.

This means that with too light an application, your SPF 50 actually protects you like an SPF 15 to 20. The recommended amount for the face alone is about half a teaspoon — more than most people use on their entire face and neck combined.

Reapplication: the most neglected point

Sun filters degrade under the effect of UV, heat, sweat, and rubbing. Sunscreen applied in the morning does not effectively protect in the afternoon.

The basic rule: reapply every two hours in case of direct exposure. For a normal office day with limited exposure, a morning application is still sufficient. But for a lunch on the terrace, an afternoon outdoors, or a beach vacation, reapplication is non-negotiable.

Sun and vitamin D: the paradox

This is where the conversation gets more complex. The sun is the main source of vitamin D for the body. Vitamin D plays a fundamental role in bone, immune, and cardiovascular health. And vitamin D deficiency is very common in countries with low sunlight.

The most consensual position currently: 10 to 20 minutes of exposure per day, outside the most intense hours — before 11 am or after 4 pm — with forearms and legs exposed, is sufficient to maintain a correct level of vitamin D for most phototypes. This moderate exposure represents a limited UV risk and preserves vitamin D synthesis without sacrificing skin protection.

Mineral or chemical filters: which to choose

Sunscreens use two fundamentally different types of filters.

Mineral filters — zinc oxide and titanium dioxide — form a physical screen on the skin's surface that reflects UV rays. They are generally better tolerated by sensitive skin and acne-prone skin. Their main drawback is a white cast, although modern formulations have significantly improved this point.

Chemical filters — about twenty molecules authorized in Europe — absorb UV rays and convert them into heat. They are lighter in texture and do not leave a white cast. Some molecules raise questions about their potential endocrine disruption, and European authorities regularly re-evaluate their safety. For sensitive skin or people wishing to avoid controversial chemical filters, mineral formulas represent the safest option to date.

Antioxidants: the second line of defense

Sun protection is not limited to UV filters. Antioxidants play an essential complementary role by neutralizing free radicals that filters have not blocked — they do not act on the same mechanism.

An optimal morning routine combines a topical antioxidant applied before sunscreen. The two reinforce each other: the filter reduces the amount of incoming UV rays, the antioxidant handles residual damage.

What your diet has to do with it

This is perhaps the least known point. Your diet truly influences your skin's resistance to UV rays.

A diet rich in carotenoids — beta-carotene from carrots and sweet potatoes, lycopene from cooked tomatoes — provides slight internal photoprotection. Not enough to replace sunscreen, but real and scientifically documented. Omega-3s found in fatty fish, nuts, and flaxseeds reduce the inflammatory response to UV rays. Dietary vitamin C supports collagen production and the skin's antioxidant defenses. Eating well for your skin isn't just a wellness slogan: it's a biological reality.

Sun spots: how to prevent and treat them

Why spots appear

When UV rays stimulate melanocytes — the melanin-producing cells — excessively or repeatedly, localized hyperpigmentation can develop. These brown spots, often called sun spots or age spots, are the result of years of accumulated UV exposure. They are more common on fair skin, after age 40, and on the most exposed areas: face, décolleté, hands, forearms.

Prevention: better to avoid than to treat

The best way to treat sun spots is not to let them appear. Daily sun protection, including in winter and on cloudy days, is the most effective preventive measure against sun-induced hyperpigmentation. And if spots are already present, continuing to expose yourself without protection reinforces them and makes any topical treatment ineffective.

The active ingredients that really work

Once spots have settled in, several active ingredients have proven their effectiveness.

Tranexamic acid is now considered one of the most effective and best tolerated depigmenting active ingredients on all skin types. It works by interrupting the signal that triggers melanin overproduction. Clinical studies show visible results in 4 to 8 weeks of regular use. It is the key active ingredient in Nocée Unifying Serum, formulated to work precisely on spots, uneven complexion, and lack of radiance linked to sun exposure.

Niacinamide inhibits the transfer of melanin to the skin's surface cells. It is well tolerated by sensitive skin and can be used morning and evening.

AHAs — glycolic acid and fruit acids — accelerate cell renewal, which helps to more quickly eliminate pigmented cells on the surface. Their use in the evening is recommended as they increase photosensitivity.

What your diet has to do with it

This is perhaps the least known point. Your diet truly influences your skin's resistance to UV rays.

A diet rich in carotenoids — beta-carotene from carrots and sweet potatoes, lycopene from cooked tomatoes — provides slight internal photoprotection. Not enough to replace sunscreen, but real and scientifically documented. Omega-3s found in fatty fish, nuts, and flaxseeds reduce the inflammatory response to UV rays. Dietary vitamin C supports collagen production and the skin's antioxidant defenses.

The sun routine that really works

Sun protection is the most effective and accessible anti-aging care available. No need for overpriced serums or complex routines. Just the right actions, in the right order.

If you're looking to identify the most suitable active ingredients for your skin type before building this routine, our complete guide to choosing your serum according to your skin type details the most consistent combinations.

What to remember

The sun is neither an absolute enemy nor a harmless source of energy. It is a powerful natural element that your skin can manage intelligently if you give it the means.

• Protect yourself daily with an appropriate SPF — not just in summer.
• Apply enough: half a teaspoon for the face and neck.
• Reapply every two hours in case of direct exposure.
• Support your skin's defenses with topical antioxidants in the morning.
• Treat existing hyperpigmentation in the evening, with clinically proven active ingredients.
• Expose yourself moderately during gentle hours to maintain your vitamin D.

Sustainable sun beauty doesn't come from forced tanning. It comes from healthy, well-nourished, and intelligently protected skin. Less involuntary exposure, more chosen protection.