How does sun protection work?

Exposure to the sun can cause sunburn and chronic damage to the skin and cells, including premature ageing and skin cancers, even though the atmosphere generally absorbs 100% of UVC, 90% of UVB and about 5% of UVA. This is why prevention programmes have been established to encourage people to take appropriate and immediate measures to prevent long-term problems. The use of sunscreens is an integral part of the strategy to reduce the skin's exposure to the sun's UV radiation. If used correctly, it serves to protect the skin from the photodegrading effects of the UVA and UVB wavelengths of the solar spectrum, by reducing the intensity of UV rays that affect the epidermis.

Whereas in the past they only offered modest protection against UVB and none against UVA, sunscreen products are now formulated to counteract the penetration of UVA and UVB rays before they reach the deep layers of the epidermis and dermis. This property is due to the action of the active ingredients present in sunscreen products: the UV filters which are often of mineral origin (UV reflectors) or chemical (UV absorbers) or a combination of both in order to provide broad-spectrum protection. Although both filters offer identical levels of protection, they operate in different ways.

• The inorganic filters , or minerals, in the form of particles ranging from 100 to 300 microns, function mechanically. They work by reflecting and scattering UV rays, forming a protective barrier on the skin's surface, thus preventing their systemic penetration into the skin. However, their tendency to create a whitening effect and to stain clothing makes them undesirable for most consumers, hence the introduction of nanoparticle forms of physical sunscreens to correct this undesirability and improve cosmetic acceptability, by reducing the whitish appearance.

  Example : Zinc Oxide (INCI: Zinc Oxide) and Titanium Dioxide (INCI: Titanium Dioxide).

• The organic filters, also known as chemical filters, directly absorb different wavelengths of UV rays in the range of UVA and UVB, instead of the skin's constituents. These agents transform the incident light into energy in the form of generally imperceptible heat or fluorescence through internal conversion mechanisms. Each filter protects within a given range of wavelengths. However, in addition to causing contact allergies, most chemical filters are suspected of being potential endocrine disruptors, carcinogenic, or harmful to the environment.

  Example : Theoxybenzone (INCI: Benzophenone-3), theoctocrylene, diethylamino hydroxybenzoyl hexyl benzoate (INCI: Diethylamino Hydroxybenzoyl Hexyl Benzoate), bemotrizinol (INCI: Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine), theavobenzone (INCI: Butyl Methoxydibenzoylmethane), ethylhexyl triazone (INCI: Ethylhexyl Triazone), disodium phenyl dibenzimidazole tetrasulfonate (INCI: Disodium Phenyl Dibenzimidazole Tetrasulfonate), thehomosalate, the 4-methylbenzylidene camphor, the octyl methoxycinnamate (INCI: Ethylhexyl Methoxycinnamate), ensulizole (INCI: Phenylbenzimidazole Sulfonic Acid) etc.

In the European Union, all sunscreens are regulated according to Annex VI of Regulation (EC) No 1223/2009 of the European Parliament and of the Council of 30 November 2009. 28 sunscreens are approved by European regulation, comprising 26 chemical filters and 2 physical filters (34 in Australia and 17 in the United States).