Ultraviolet rays cause sunburn and skin cancer, so sunscreens are essential for sunbathing. But why doesn’t an SPF of 60 provide double the protection of an SPF of 30?
Summer is here and sunscreen products in their hundreds are back on the shelves of supermarkets and pharmacies. The vast global sunscreen market, however, continues to be affected by controversies over the usefulness and correct use of sunscreens and regulatory differences. Everyone wants the golden tan dictated by fashion. But leaving aside the aesthetic issues, sunlight in small quantities stimulates vitamin D synthesis, reduces blood pressure and improves peripheral blood circulation. The sun is also good for skin ailments such as psoriasis. But nowadays, everyone knows that excessive exposure to the sun that so attractively tans us can also cause health problems such as sunburn, skin ageing and even cancer. While we all use sun protection as part of our normal sunbathing or swimming routine, do we know what it is we are protecting ourselves from and how much protection we need?
The fact is that skin cancer incidence continues to rise at an alarming rate worldwide and dermatologists increasingly insist that sun protection is essential, especially at an early age.
Invisible but dangerous
Exactly what happens when we sunbathe? Among other elements, natural sunlight delivers photons of ultraviolet (UV) light that are invisible to the naked eye. Long-wave and medium-wave UV rays are called UVA and UVB rays, respectively. UVB only reaches the outer layer of skin but is the main cause of sunburn and DNA damage. UVA penetrates deeper within the skin and produces the free radicals that cause premature skin ageing and some immunological problems. Excessive doses of either UVB or UVA rays causes skin cancer.
What’s in a sunscreen?
Sunscreens contain both organic and inorganic ingredients that combine as a thin layer that prevents UV rays from reaching and damaging the skin. There are dozens of organic components, which absorb and neutralize the UV rays; different sun protection brands have their own formulations and even their own patented molecules. The inorganic components, also known as screens or blockers, are usually pigments that reflect or deflect UV rays. The most common inorganic components are titanium dioxide and zinc oxide. A good sunscreen should contain a suitable combination of both to be truly effective.
Some sunscreen ingredients are not specific to photoprotection but give the product its tactile, visual and aromatic properties. A variety of presentations are available on the market, including creams, lotions, foams, gels, sprays, lotions, sticks, etc, as well as combinations of these. Although the formula is clearly a key element, the type of presentation adapts a sunscreen to a particular use: full block, children, high altitudes, sunbathing, sailing, etc. Labels and packaging also provide other information, frequently citing properties such as:
• Hypoallergenic (to avoid allergic reactions)
• Non-comedogenic or non-oily (to prevent acne)
• Water-resistant or waterproof
• Anti-jellyfish (to neutralize the sting of common jellyfish species)
• For sensitive skin (especially suitable for babies)
• Resistant to abrasion or friction (for outdoor types)
• Biodegradable (environmentally friendly)
• Anti-wrinkle (with moisturizing compounds).
Which sun filter – SPF 15, 30 or 50?
The sun protection factor (SPF) tells us how long a sunscreen will protect us when applied to the skin. The SPF scale works as follows: 10 out of every 100 photons attacking our skin will pass through a protective filter of 10, but only 5 will penetrate an SPF-20 product and only 2 will penetrate an SPF-50 product. In practical terms, this means that an SPF of 10, 20 or 50 allows us to remain in the sun 10, 20 or 50 times longer than when unprotected.
However, friction and other external factors - such as water when we swim - weaken the barrier, so the effective safe period is actually far lower. Experts therefore recommend using sunscreens with an SPF of 15 to 50, because below 15 affords little protection, whereas more than 50 simply misleads consumers as it does not guarantee much higher protection.
Many studies published in recent years, such as this New Scientist article, state, in fact, there is no 100% safe product that protects us fully from the carcinogenic effects of sunlight. Curiously, Spanish researchers have developed a sunscreen containing silicon microspheres – not yet on the market – that provides protection against the infrared radiation also known to be harmful to the skin.
How should we sunbathe?
It is important to match exposure time to the SPF of our sunscreen and occasionally cover up with light clothing. The best advice is, however, to sit in the shade from time to time and avoid the kind of lengthy exposure only lizards can endure. Follow these practical tips:
• Avoid sunbathing in the middle of the day
• Apply sunscreen 30 minutes before exposure to the sun
• Apply a generous layer of sunscreen to all exposed areas, including the ears, neck and feet (you need about 30 mL to cover the entire body)
• Repeat applications every hour and after each swim
• Spray aerosol sunscreen onto your hand and then spread it on your body to avoid inhalation.