Billions of people live on the earth and each has his or her own color of the skin. In human body the skin color depends on the quantities of melanin, carotene and oxygenated or reduced hemoglobin combined in the skin, as well as the thickness, water content etc. Among other factors, the quantity of melanin that is distributed in the skin determines its fairness or darkness and greatly influences the human complexion, at the same time melanin plays an important role in minimizing the damage that UV rays cause in the skin.
Electromagnetic radiations of wavelength between 150 and 400 nm are termed as Ultraviolet rays. Approximately 10% of sun’s energy is in the form of ultraviolet radiations. Atmosphere absorbs most of the noxious radiations emitted by the sun, only 5% of the harmful radiations reach to the surface of the earth.
Ultra violet Protection Factor (UPF)
UPF measures the effectiveness of textile fabrics in shielding the human skin from UV radiation. It is expressed as the relative amount of time required for the skin to show redness with and without the textile material under regular exposure to solar radiations. If a person experiences skin redness on exposure to sun after 10minutes, then on wearing a textile material of UPF 20 he would experience the same amount of skin redness after 200 minutes. A UPF score of 30 indicates that only 1/30th of the UVR striking the fabric surface essentially passes through it. Higher the UPF of a textile, the better is its ability to guard the skin it covers.
| Protection Category | UPF Range | UPF Values Allowed on Labels | Approximate % UV Blocked |
| Good UV Protection | 15 – 24 | 15 and 20 | 93.3% – 95.8% |
| Very Good UV Protection | 25 – 39 | 25, 30 and 35 | 96.0% – 97.4% |
| Excellent UV Protection | 40 – 50+ | 40, 45, 50 and 50+ | 97.5% – 98.0% |
The higher the UPF number, the higher shall be the protection from harmful UV rays.
A fabric must have a minimum UPF of 30 to qualify for The Skin Cancer Foundation’s Seal of Recommendation.
By using UV absorbers, exposure of the fabric to UV lights is reduced on the one hand as well as the intensity of the transmitted UV light on the other. To indicate the protection from UV radiation the term Sun Protection Factor {SPF} is widely used. SPF is a measure of how much a sun screen protects the skin protection products. SPF is a measure of how a sun screen protects the skin from burning and is measured by timing, as to, how long skin covered with sun screen .The term Ultra Violet Protection Factor { UPF } is widely used by the textile and clothing industry.
Coating the surface of textiles and clothing with nano particles is an approach to the production of highly active surfaces to have UV blocking properties. Zinc oxide {Zno} nano particles embedded in polymer matrices like soluble starch are a good example of functional nanostructures with potential for applications such as UV. Metal oxides like Zno as UV blocker are more stable as compared to organic UV blocking agents. Hence nano Zno will enhance the UV blocking property due to their increase surface area and intense absorption in the UV region.