An attempt to analyze the Ultraviolet A and B radiations and their effects. In this article, we will also explore sunscreens, their role in protecting against the Ultraviolet radiations and different categories of sunscreens.
Ultraviolet A and B and their effects
Ultraviolet radiation that reaches the earth's surface is composed of two types of radiations: Ultraviolet A (UV-A) and Ultraviolet B (UV-B).
UV-A is also known as blacklight. It is responsible for skin tanning and is generally not much harmful. UV-A rays have longer wavelength that can damage the skin connective tissues and even lead to premature aging. In general, UVA is less harmful but it can contribute to DNA damage and possibly skin cancer. Due to its long wavelengths, it penetrates deeply into the skin. However, it cannot be measured in SPF testing as it does not cause any reddening or sunburns on skin .
UV-B is a small wave UV but the most dangerous part of the sunlight. Any long term exposure to UVA could result in unhealthy effects on the skin and eyes. UVB is the most common cause of screen burns and the most likely to cause skin cancer. Overexposure to UVB light is hazardous to eyes also and may lead to cataract and other eye diseases.
As sunlight passes through the atmosphere, 90% of UVB radiation is absorbed by the ozone layer whereas UVA radiation is less affected by the atmosphere. Therefore, the sunlight that reaches the earth's surface mainly consist UVA with small quality of UVB components. Since the ozone layer prevents the most harmful UVB radiations to reach the earth's surface, its depletion is likely to intensify existing health effects caused by exposure to UV radiation. As the ozone layer becomes thinner due to pollution in the atmosphere, the protective filter provided by the atmosphere is reducing rapidly. As a result, human beings and the environment are exposed to higher UV radiation and are more prone to adverse health effects “. Thus both Ultraviolet A and Ultraviolet B do penetrate the ozone layer in attenuated form, reach the surface of the earth and cause harmful health diseases. For this reason skin and cancer specialists propose that people must use sunscreens that are able to block both kinds of radiation -- ultraviolet A and B.
Purpose of sunscreens
Sunlight is a basic need for every human being. About 15 minutes of sun exposure a day is sufficient for the body to make Vitamin D, which is considered to be an important element for healthy development of bones and teeth. But its overexposure may cause many harmful effects, from wrinkles to skin cancer. Sunscreens help protect against the sun's damaging effects. Sunscreen provides SPF protection to the skin and is able to filter both UVA and UVB radiations. Though sunscreens might not be effective in protecting against the most dangerous forms of cancer but if used properly, sunscreen can play an important role in protecting human skin from the most harmful effects of UV radiations emitted by the sun.
Sunscreens protect the skin by absorbing or reflecting UVA and UVB rays. For sunscreens to be effective, all sunscreens must contain sun protection factor (SPF) level. The SPF depicts the protection that a sunscreen can provide against the sunburn when used appropriately.
Sunscreens contain a number of chemical ingredients that are able to absorb UVA and UVB radiations. Some of the common chemical ingredients contained in sunscreens are titanium dioxide and zinc oxide. They reflect, scatter, and absorb both UVA and UVB rays. These ingredients, does not cause any allergic reactions. Moreover, with the advancement in technology, the particle sizes of zinc oxide and titanium dioxide have been reduced, making them more effective without losing their ability to screen UV. For maximum effectiveness, sunscreens should be applied to clean dry skin 15 minutes before the exposure to sunlight and must be re-applied every 30 minutes after exposure to the sun. However, using sunscreen does not mean it is safe to long exposure to the sun, especially when the index level UV rays are high. Although a sunscreen with an SPF of 15 or higher offers protection from sunburn, it does not block all of the sun's damaging rays. In order to get full protection from its damage, other alternatives such as minimize peak hours of sun exposure, and wear protective clothing in addition to applying sunscreen are also necessary .
Categories of sunscreens
Sunscreens can be classified into two categories:
Physical sunscreens
Chemical sunscreens
Physical sunscreens are also referred to as sunblocks. Sunblocks provide protection against both UVA and UVB radiations. They generally contain particles such as titanium dioxide and zinc oxide which physically block ultraviolet radiation (UVR). These are the particles that are naturally occurring in minerals. Since they consist of natural minerals, physical sunscreens are gentle on the skin, making them a good choice for those who suffer from ache or rashes. These minerals work as they scatter, reflect, or absorb the suns radiation. These products have advantages over chemical sunscreen as they cause much less irritation since they are in the form of insoluble particles that are not absorbed through the skin. Because of the small size of the particles, modern physical sunscreens are able to reflect UVA and UVB radiation better than earlier products did. One more advantage of physical sunscreen is they do not penetrate the skin and thus they are not absorbed. Examples of physical sunscreens are:
titanium dioxide
zinc oxide
magnesium oxide
magnesium silicate (talc),
kaolin, iron derivatives and red petrolatum
Chemical sunscreens consist of chemical substances such as such as benzophenone or oxybenzone. They prevent sunburns as they are powerful absorbers of the Ultraviolet rays. These products have the advantage that they penetrate the skin and protect it from UV rays from within. When applied on skin, they feel light and leave no visible mark. They generally contain high levels of SPF protection than physical sunscreens. But since they penetrate the skin, they can irritate the sensitive skin and need time to absorb into the skin. Therefore, they must be applied 20 minutes before heading out. Some chemical sunscreens offer a wide spectrum of protection because they also contain physical sun blocking agent. Examples of physical sunscreens are:
