University of São Paulo: Interaction between naturally occurring antioxidants and sunscreens may increase photoprotective efficacy

THEaddition of antioxidants of natural origin to sunscreen formulations can guarantee greater protection against ultraviolet radiation, shows a study by researcher Thamires Batello Freire. In her Ph.D. Influence of antioxidants on the photostabilization of avobenzone (UVA filter) and octyl p-methoxycinnamate (UVB filter) in photoprotectants , she evaluated the interactions between photoprotective agents and the antioxidants resveratrol (found mainly in grape skins) and ferulic acid (present in several natural sources). The work, carried out at the Faculty of Pharmaceutical Sciences (FCF) at USP, was supervised by Professor Maria Valéria Robles Velasco.

In an interview with Jornal da USP , Thamires explains that sunscreens are substances that, upon receiving electromagnetic waves from solar radiation, absorb the energy transmitted by them, protecting the skin from solar damage. They may have more than one active component, as some sunscreens are more efficient against ultraviolet A (UVA) rays and others against ultraviolet B (UVB) rays.

The Sun emits ultraviolet radiation, which are electromagnetic waves: UVB rays are short waves, between 290 and 320 nanometers (nm) and more energetic, which reach the epidermis (first layer of the skin), causing redness (erythema), burns and damage. directly to the DNA, which can lead to the appearance of skin cancer. UVA rays are formed by longer waves (between 320 and 400 nm), with less energy, which reach the dermis (deeper layer) and can degrade collagen and elastin fibers, favoring skin aging. In addition, UVA rays can cause the release of free radicals (reactive molecules that can cause damage to cells) which, when interacting with DNA, can also result in skin cancer.

Antioxidants, generally used in cosmetics due to their action against the signs of aging, are substances capable of protecting the body against the action of free radicals. The research used these elements in order to increase the effectiveness and safety of sunscreens, which may undergo physical-chemical changes due to the absorption of the sun’s rays or the presence of other filters, active principles or product components. “During the tests, we realized that the antioxidants enable the energy absorption of the sunscreen through different mechanisms”, says Thamires.

Rutin-based sunscreen is antioxidant and increases protection by up to 70%
The interaction between filters and antioxidants

In experiments with animal cells, Thamires worked with avobenzone (UVA filter) and octyl p-methoxycinnamate (UVB filter) in the company of the antioxidants resveratrol and ferulic acid. “In the cosmetics sector, it is common to appeal to the natural with the use of components of plant origin, such as those found in extracts, oils and waxes. This is because those of animal origin can cause allergies because they contain amino acids that are recognized as foreign substances by the body,” he explains. The tests were performed using Thermal Analysis, Nuclear Magnetic Resonance, Electronic Paramagnetic Resonance and fluorimetric (FRET and fluorescence inhibition) techniques.

The researcher explains that, by absorbing ultraviolet radiation, the molecules of organic sunscreens are excited and the electrons in the atoms migrate to a higher energy orbital. Upon returning to its original state, the electron releases the absorbed energy in a less energetic form. With the addition of antioxidants to the solutions, the molecules return to their original state and capture the radiation again, increasing the photostabilization and absorption capacity of the analyzed filters.

During the test, the antioxidant resveratrol inhibited the fluorescence of solutions B and C, which contained the avobenzone filter. Image: Personal Archive/Thamires

For Thamires, the trend of using sunscreens with antioxidants should continue to be followed by the cosmetics industry due to their multifunctional use of protection against damage caused by ultraviolet rays and skin aging. “For this, it is necessary to publish more scientific articles that prove the effectiveness, in addition to the interest of companies in the sector for the introduction of these formulas in the market”, he says.

Skin cancer

According to data from the World Health Organization (WHO) released in 2021, it is estimated that there will be an incidence of 2 to 3 million cases of non-melanoma skin cancer and more than 130,000 cases of melanoma skin cancer worldwide annually. Despite the lower incidence, melanoma (originating in cells that produce melanin) is more aggressive and responsible for most deaths, while non-melanoma has a better prognosis.

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