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 multiplying. But behind the well-rehearsed prevention messages lies a more nuanced reality—and one more useful to know.

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

What the sun actually does to your skin

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 midday in direct sunlight, they reach their peak. The SPF index primarily protects against these.

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

A significant portion of the visible skin aging you attribute to age or genetics is very often the result of decades of unprotected UVA exposure.

Oxidative stress is one of the central mechanisms for understanding why the sun accelerates skin aging.

When UV rays hit 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 new collagen production, 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, and melatonin produced during sleep.

But in the face of intense and repeated sun exposure without protection, these defenses can be overwhelmed. This is precisely where antioxidant active ingredients in cosmetics can supplement the skin's natural defenses.

SPF: what the index doesn't tell you

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

The difference between SPF 30 and SPF 50 is therefore relatively small in terms of UVB protection. This doesn't mean a high SPF is useless, but it puts the obsession with very high SPFs into perspective.

What also matters is the quality of UVA protection and especially the amount of product applied.

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.

With too light an application, the actual protection achieved can be much lower than that advertised on the product. For the face alone, the recommended amount is about half a teaspoon when taking into account the quantity needed to achieve the protection measured in the laboratory.

Reapplication is also essential. Sunscreens are gradually altered by UV rays, heat, perspiration, and friction.

For direct and prolonged exposure, the basic rule is regular reapplication, especially after sweating, swimming, or wiping your face.

Sun and Vitamin D: The Paradox

This is where the conversation gets more complex. The sun is the body's primary source of vitamin D. Vitamin D plays a fundamental role in bone, immune, and cardiovascular health.

Moderate sun exposure therefore contributes to vitamin D synthesis. But this reality does not mean that one should deliberately seek significant or prolonged exposure without protection.

Sun protection and vitamin D are not necessarily contradictory. Vitamin D needs can also be met through diet and, when necessary, with medical advice.

Mineral or chemical filters: how to choose?

Sunscreens use different types of filters, including mineral and organic filters.

Mineral filters, such as zinc oxide and titanium dioxide, are used in sunscreen formulations to protect the skin from UV radiation. They can be particularly appreciated by some sensitive skin types. Their main drawback can be their white cast, although modern formulations have significantly improved this point.

Organic filters absorb UV radiation and generally allow for lighter, more transparent textures. Their safety is evaluated under European regulations, and authorized filters are regularly re-evaluated.

The choice should therefore primarily consider your skin's tolerance, the quality of UVA and UVB protection, the texture, and your ability to apply enough product.

A sunscreen you like enough to apply correctly and regularly will always be more useful than a product you only use occasionally.

Antioxidants are a second line of defense. Sun protection is not just about UV filters. Antioxidants can supplement their action by neutralizing some of the free radicals generated by exposure.

A morning routine can thus combine an antioxidant active ingredient with sun protection. The filter reduces the amount of radiation reaching the skin, while the antioxidant acts on residual oxidative damage.

Sun spots: how to prevent and treat them

When UV rays stimulate melanocytes—melanin-producing cells—excessively or repeatedly, localized hyperpigmentation can appear.

These brown spots, often called sun spots or age spots, are the result of accumulated UV exposure over time. They appear particularly on regularly exposed areas: face, décolleté, hands, and forearms.

The best way to treat sun spots is to limit their appearance. Regular sun protection is therefore essential to prevent them and to keep existing spots from getting darker.

Once spots have appeared, several active ingredients can be integrated into a targeted routine.

Tranexamic acid is notably used in treatments designed to address the appearance of spots and uneven skin tone. It acts on the mechanisms involved in excessive melanin production.

It is the key active ingredient in Nocée Unifying Serum, formulated to work on spots, uneven complexion, and lack of radiance.

Niacinamide can also be interesting for skin with pigment irregularities. It acts notably on the transfer of melanin to the skin's surface cells and can be used in a regular routine.

AHAs, such as glycolic acid and some fruit acids, accelerate cell renewal and can help gradually improve the appearance of the complexion. Their use must, however, be adapted to the skin's sensitivity and accompanied by sun protection.

What your diet has to do with it

Your diet also influences your body's ability to fight oxidative stress.

A diet rich in carotenoids—beta-carotene from carrots and sweet potatoes, lycopene from tomatoes—contributes to the body's antioxidant defenses.

Omega-3s, found notably in fatty fish, nuts, and certain seeds, also contribute to the balance of the inflammatory response.

Dietary vitamin C, for its part, contributes to normal collagen production and antioxidant defenses.

This obviously does not replace sun protection. But how you nourish your body also contributes to how your skin responds to external aggressions.

The sun routine that really works

Sun protection is one of the most effective ways to limit UV-related skin aging. No complex routine is needed: the key is to implement the right steps, in the right order, and above all, to maintain them.

If you're looking to identify the most suitable active ingredients for your skin type before building your routine, our complete guide to choosing your serum according to your skin type will help you better understand the different options.

Key takeaways

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

Sun protection must be regular. It's not just for summer days spent at the beach. UVA rays are present all year round and contribute to skin aging.

Quantity matters as much as the SPF. Sun protection applied in insufficient quantities will not provide the level of protection indicated on the product.

Reapplication becomes essential during prolonged exposure. Sports, beach, mountains, terraces, or swimming require particular attention.

Antioxidants complement sun protection. They can help support the skin's natural defenses against oxidative stress.

Spots are primarily prevented. An anti-spot routine can help even out skin tone, but it must always be combined with appropriate sun protection.

Lasting sun beauty doesn't come from forced tanning. It comes from healthy, well-nourished, and intelligently protected skin.

Less involuntary exposure. More chosen protection.