Filter ultraviolet

A filter Ultraviolet is a substance able to filter some Radiation S to protect the skin against the harmful effects of these radiations. The ultraviolet filters are the active ingredients of the sun lotions. There exist two types of ultraviolet filters: chemical filters and mineral filters.

Chemical filters

In fact organic chemical compounds absorb the light Ultraviolet you. There exists a great chemical number of filters. Each chemical filter protects in a range given from wavelengths. For a protection against all the ultra-violets, it is necessary to associate several different filters.

When the solar molecule of filter receives an ultraviolet radiation, it passes in a excited state. It turns over in its stable condition by a relieving by dissipating the energy received by vibrations ou/et by re-emitting a less dangerous radiation for the skin (Infrarouge for example). Once in its stable condition, the molecule is again ready to receive ultraviolet light and to continue the cycle of protection. The chemical filters act in the same way that the Mélanine, which is a natural filter of the Peau.

The chemical filters are absorbed by the skin. Certain chemical filters can cause photoallergic Allergie S, irritations or reactions (allergy in the presence of Sun due to the product applied to the skin).

According to recent studies, certain chemical filters would be able to behave like Hormone S females.

Mineral filters

One speaks also sometimes about screens or physical filters. The mineral filters are inert and opaque powders which reflect the Lumière. It is the zinc oxide (ZnO) and the titanium dioxide (TiO₂) which are used in the sun lotions. These Pigment S white reflects and diffuses radiations UV (UVA and UVB), but also part of the visible light, while acting like a mirror.

For a long time, the disadvantage of the mineral filters was the white traces formed on the skin, which had with the reflection of the white light. This problem was solved by reducing the mineral filters in micropigments, particles moreover small size which reflect UV but not the visible light. That includes the use of nanoparticules.

The mineral filters do not cause allergies. One thus finds them in the solar produced intended for the sensitive skins and the children.

The mineral screens do not penetrate in the skin but remain on the surface. Compared to the chemical filters, they are more difficult to spread out.

The effects of the use of the nanoparticules on the human body are unknown.

Photostability

To be powerful, a filter UV should not be degraded under the effect of the Lumière: it must be photostable. A product not photostable sees its effectiveness decreasing as from a certain duration to the sun.

A molecule of filter which receives light UV passes in a excited state, then it turns over in its stable condition and so on. But it can happen that the excited molecule does not return in its stable condition and is transformed into another product, inactive that one. Certain solar filters are thus degraded by UV and cannot fulfill their role any more. The avobenzone for example is a filter UVA not photostable. One hour of exposure to the sun is enough to make it completely ineffective.

One can sometimes stabilize a filter not photostable by adding certain ingredients. Thus the avobenzone is returned photostable when it is in the presence of one or several of the following filters photostables: octocrylene, methylbenzylidene camphor or terephthalylidene dicamphor sulfonic acid.

UVs are also responsible for the photodegradation of the plastics and polymers. To ensure the photostability of the latter, one uses powders which absorb UVs. These UVs filters are added to the plastic during its synthesis: one uses mainly the carbon black (black pigment) and powders it silicon dioxide (white pigment).

Interactions between the ultraviolet filters and reactions with the skin

The various ultraviolet filters react together. The effect can be negative or positive.

The effect is negative for example for a mixture of avobenzone and of ethylhexyl methoxycinnamate because the avobenzone degrades the ethylhexyl methoxycinnamate.

The effect is positive when several filters act as synergy for a better protection against UV.

It is important to study the interactions between the ingredients because the majority of the solar produced combine various filters in order to obtain a good protection on all the range of the Ultraviolet S.

Other share, the chemical filters react with the Peau, causing allergies. To avoid these reactions, it is possible to insulate the filters by encapsulating them in microscopic spheres. One uses for example transparent microcapsules in Verre (Silice), whose size is from approximately 1 micrometer. The Encapsulation prevents the filters from penetrating in the skin, avoids the interactions between the filters and stabilizes them.

Comparative table of the various filters

Wavelengths of the ultra-violets:

UVA: 320 - 400 Nm

UVA: 320 - 340 Nm
UVA: 340 - 400 Nm

UVB: 280 - 320 Nm

Chemical filters

Mineral filters

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