SOLAR FILTERS
Sunscreens or sunscreens are substances capable of defending the skin from the harmful effects of Ultra Violet rays. They are divisible in chemical filters And physical filters. Chemical filters they absorb UV rays and transform them into heat before they are absorbed by the cells of the dermis and damage them. Physical filters exert their protective action by "barrier effect" and are instead made up of particles that reflect UV rays. Physical filters, when applied to the skin, form a physical barrier impermeable to UV rays.
How effective are they?
The effectiveness of sunscreens used in Europe is measured with internationally standardized tests, conducted either by manufacturers or by independent laboratories according to European legislation. The official test consists in applying on the skin of the shoulder 2 mg of cream per square cm of surface. Then the protected area is irradiated with a particular lamp and the erythema is measured (redness) produced. The redness produced in the protected area is compared to that produced in an adjacent area not protected by the cream. Since skin damage is induced by both ultraviolet type B (UV-B) is give it ultraviolet type A (UV-A), protective sunscreens must protect against both types of UV. Community legislation establishes that the protection of a cream against UV-A must be equal to at least 1/3 of the total protection.
The sun protection factor
The sun protection factor (FPS), also indicated by the English abbreviation SPF (Sun Protection Factor), is a number that indicates how much of the solar radiation is filtered by the product. An FPS of 4 means that cream lets only 1/4 of the UV rays through. This means that the protected subject can remain exposed to the same sunlight 4 times longer than it could in the absence of protection, for example 1 hour instead of 15 minutes. According to European legislation, sunscreens are classified into four groups according to the FPS factor (table 1). Products with an FPS factor greater than 50 are indicated in children (always) and in light-skinned adults when particularly high protection is required, for example on snow or water. A very high protection factor is also indicated in subjects who take drugs that increase skin sensitivity to light (eg. amiodarone, phenothiazines, etc) or carriers of dermatological diseases that worsen with exposure to the sun (eg. cutaneous porphyria). In these cases, a high water resistance is also particularly useful.
