Ultraviolet (UV) light can cause cancer and degrade materials. A UV absorber can be added to sunscreen or products to absorb or reflect harmful UV light. UVA light penetrates human skin further and can cause the most damage. UV absorbers can provide protection through absorption or reflection, while organic chemicals absorb UV light and create heat. UV stabilizers react with harmful molecules to protect products. Titanium dioxide is an effective UV protector and is commonly used in paints. Lead oxide was used in the past but is now avoided due to its harmful effects.
The sun creates a wide range of light frequencies, both visible and invisible to humans. One range of frequencies that can be harmful to skin and man-made materials is ultraviolet (UV) light, or light with frequencies above the visible violet range. Ultraviolet light can cause cancer in humans with long-term repeated exposure and chemically degrades plastics and other materials. A UV absorber can be added to sunscreen or products manufactured to absorb or reflect harmful UV light.
Three ranges of frequencies called UVA, UVB and UVC normally define ultraviolet light. Most of the ultraviolet light that reaches the earth’s surface is classified as UVA, and all types can be harmful. UVA light has the longest frequency range and has been shown to penetrate human skin further, potentially causing the most damage. UVA light was believed to be the main cause of human skin cancer, but research in the late 20th century showed a relationship between UVB and the development of cancer.
A UV absorber can provide protection in two ways. Solids such as carbon black, titanium dioxide and zinc oxide reduce UV light by absorbing it in the case of carbon black or by reflecting it away in the case of the two pure white oxides. Sunscreens, paints and some plastics use combinations of titanium or zinc oxides to provide protection. Tires and rubber products can use carbon black to protect them from light damage.
Organic chemicals can provide UV protection by chemically absorbing UV light and creating heat. These materials do not affect the transparency or light transmission of the materials. They are commonly used in clear or translucent plastics, adhesives, and clear coats. Organic absorbers to not chemically react with the materials they are protecting.
Another class of compounds used in conjunction with absorbers are UV stabilizers. These chemicals are typically classified as hindered amine light stabilizers (HALS) which chemically react with molecules formed by UV reactions with materials. HALS work as scavengers of harmful molecules that can attack and degrade plastics or other products. A UV absorber and stabilizer can be added in combination to a product formulation to provide optimal protection.
Lead oxide was used in paints for centuries as a coloring agent and UV absorber, until research in the 20th century showed a relationship between lead paint and disabilities in children. Most house paints now use titanium dioxide, a mineral produced from natural deposits of sand, as a whitening agent and UV protector. Calling mineral oxides a UV absorber is perhaps wrong, because they are reflectors that scatter incoming light. The effect is the same, however, and titanium dioxide is effective at reducing the damage caused by ultraviolet light.
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