Mineral-based sunscreens may contain zinc oxide or titanium dioxide, which create a barrier that reflects UV light before it penetrates the skin. Mineral creams are not absorbed, so older formulations in particular left the classic greasy feeling and a white layer. Today, however, research has given the public creams made with mineral nanoparticles, which rub into the skin much better.
People who dislike the texture and greasiness of mineral sunscreens turn to chemical ones, in creams or sprays. In these products too, the ingredients form a thin protective film that not only absorbs UV rays but also alters their structure, converting them into heat before they penetrate the skin.
But beware. The chemicals used are absorbed into the bloodstream. It is not uncommon, especially in recent years, to read of health authorities expressing doubts about the real effects of this absorption on the body, particularly in the long term.
What really makes the difference?
The AAD (American Academy of Dermatology) writes on its website: ‘The best type of sunscreen is the one you will use again and again’.
So let us turn to the advice of this important association of dermatologists. First of all, it recommends using a water-resistant sunscreen with a sun protection factor (SPF) of at least 30 or higher, offering broad-spectrum protection against both UVA rays and UVB rays (the ones responsible for sunburn).
But beware. This holds true in ‘normal’ conditions of heat and sun exposure. During the increasingly frequent extreme heatwaves (and the United States knows something about that this year), dermatologists advise mineral sunscreens as preferable. This is because chemical sunscreens can lose their filtering ability if exposed to extremely high temperatures.
They also stress the role of sweat which, increasing as temperatures rise and combining with the ingredients of chemical sunscreens, causes itching and skin rashes (something many of us have experienced in recent summers).
In any case, even without extreme heat, people with sensitive skin – according to the AAD – should prefer mineral sunscreens.
Other recommendations. How much cream should you apply?
The AAD estimates that most people apply only about 20–50% of the amount of sunscreen needed to obtain the stated SPF.
An adult needs one ounce of sunscreen (about 28 grams), which is equivalent to a full shot glass. So it is worth taking a measuring cup or a shot glass under the beach umbrella – without worrying about any teasing from your neighbours.
The advice is also to apply a double layer of sunscreen on the parts of the body most exposed to the sun, such as the face, chest and shoulders.
It is well known – but worth remembering – that sunscreens must be reapplied at least every two hours and after swimming or sweating. During a heatwave you sweat more, so you will need to apply them even more often.
Keep your sunscreen away from excessive heat
Although this recommendation may seem trivial, it should not be underestimated.
Temperatures inside cars or beach bags can be much higher than in the open air. Eight hours of exposure to temperatures of 30 to 50°C and more – which cars left in the sun reach – can irreversibly alter the physical characteristics of a chemical sunscreen and greatly reduce its effectiveness.
Sunscreen should be stored in a cool, dark place. If the room or place is too hot, it should be put near the fridge, or by the ice pack.
