Chemical and physical sunscreens work in different ways

The first commercially available sunscreen came in 1928 in the United States. However, for a long time little or no attention was paid to photoprotective agents. Only in 1943, a chemical filter, PABA (para-aminobenzoic acid) was patented as the first established sunscreen. However, it was in the 1970s that the popularization of photoprotective agents, primarily of the UVB type, occurred. Protective filters for UVA appeared in the 1980s and 1990s with the physical filters titanium dioxide and zinc oxide, respectively.

Sunscreen is a product designed to block the sun and protect or harbor skin cells against the harmful effects of ultraviolet radiation, among the most important of them: sunburn and skin cancer. These local-use medications have several different formulations containing products and ingredients that are able to reduce the harmful effects of solar radiation. The basic mechanisms by which these substances act are: reflection, dispersion, and absorption of ultraviolet light.

Understand the Difference

Physical filters, also known as inorganic, are particles derived from metals, or metal oxides, which act through optical mechanisms, reflecting or dispersing the sun's rays. The main physical filters are zinc oxide and titanium dioxide. Currently, they are also available in nanoparticles, which gives a more discreet coloration than the previous formulations, which left the skin looking whitish or coppery. In general, they are associated with chemical or organic filters for better coverage in relation to the ultraviolet spectrum. The advantage of this type of filter is that they are more stable and do not penetrate the skin, being ideal for allergic patients with high skin sensitivity.

Chemical filters are molecules that absorb ultraviolet radiation through chemical reactions, entering "in front of cutaneous pigments in their greed for solar energy. In this way, they absorb this radiation, preventing it from reaching the skin cells. Depending on the range that each molecule acts, it will be considered a broad spectrum sunscreen (acts in the UVA and UVB range) or exclusive UVA or UVB. In general, marketable sunscreens contain more than one molecule to act on a wider range. However, in relation to the physical filters, they have a lower stability, as they "saturate" their capacity to absorb energy over time, requiring frequent reapplications if the exposure is prolonged. In addition, this sunscreen can penetrate the skin and react with it, leading to allergic and photoallergic reactions (triggered by the sun itself).

Who should use each of the

types From the above, it is clear that filters physical therapies are the most appropriate for pregnant women and children, in addition to the aforementioned patients with previous allergy to sunscreens and those with sensitive skin or sensitized by dermatological procedures.

However, for patients who do not have this type of restriction or which have skin diseases such as: previous skin cancer, solar urticaria, lupus, skin patches and very light skin, suffering from sunburn, broad spectrum sunscreen may be more appropriate, and chemical filters, associated or not to physicists, are a more interesting alternative. Patients with brown or extremely oily skin benefit from chemical filters, and in the latter, we can choose an association of these substances with ingredients that absorb oil, without compromising the photoprotective action.Sun Protection Factor

But no matter what type of protector, the SPF (sun protection factor) follows the same principle. It quantifies the protection that a given product is able to offer, in terms of exposure time, against sunburn compared to unprotected exposure. Thus, if a particular protector has the value of SPF 30, this means in practice that 30 times more sun exposure is required to produce skin redness when compared to the situation in which this user would be without the product. However, this time is strongly influenced by personal and environmental factors, such as the individual response to burn, in which the skin type is important? lighter skins will react sooner than darker skins, for example. The ultraviolet index (UVI) of that day, the exposure time, the region of the body and the type of soil where the individual is located (fine white sand reflects more the sun than the pool floor, for example.)

For this reason, it is essential to take into account medical advice on the need to reapply the sunscreen, which should be individualized according to the factors mentioned above and also according to the presence or absence of disease or condition of the patient's skin.

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