Skin exposure affects the skin in many ways. In the short term, it can lead to reddening, irritation, and eventually tanning, which is the main reason for most people sunbathing.

There are, however, long-term effects of UV radiation, which are irreversible and often malignant. Sun exposure is now increasingly recognized as the possible cause of premature wrinkling and various types of skin cancer. For these reasons, sun protection has become a very important issue today. 

UV filters, ingredients that can effectively protect the skin from UV radiations, are now incorporated not only into sunscreens but also in daily-use cosmetics, such as moisturizing lotions, foundations, and lipsticks. Appropriate skin care should follow any type of sun exposure to help the skin maintain its integrity and barrier function. 

Below we are going to discuss major types of UV radiation and their positive and negative effects on the human body. It reviews sunscreen ingredients, the major product types, and their characteristics. The major sites that can be taken to increase the product's efficacy are also discussed.

Sun Protection Basics
The Light Spectrum:
The sun emits a constant flow of energy in the form of electromagnetic radiation, which ranges over a wide spectrum of wavelengths. The electromagnetic spectrum is divided into categories defined by the size of wavelength frequency, and energy.

Radio waves at the bottom of the spectrum have the lowest energy and lowest frequency; their wavelengths are long with peaks far apart. Microwave radiation has higher energy, followed by infrared waves, visible waves, UV rays, and X-rays. At the top of the spectrum, gamma rays have the highest and the shortest wavelength with peaks closer to one another.

Most electromagnetic radiation from space is unable to reach the surface of the earth due to the earth's atmosphere. The electromagnetic waves reaching us consist of only a portion of the UV light, visible light, a portion of infrared rays (near-infrared light), and radio waves. Consequently, the surface of our planet is not exposed to cosmic rays, gamma rays, and X-rays, each of which is potentially lethal. Of the wavelengths of the radiation that reach the earth's surface, UV has the highest energy. Therefore, it has the highest importance in relation to sun exposure.

UV radiation represents 5% of the total solar radiation reaching the earth's surface. As sunlight passes through the atmosphere, all UVC and approximately 90% of UVB radiation are absorbed by ozone, water vapor, oxygen, and carbon dioxide. UVA radiation is less affected by the atmosphere.

Therefore the UV radiation reaching the earth's surface is largely composed of UVA (approx. 95%) with a small UVB component (approx. 5%).

UV radiation can be divided into three categories based on wavelength. They differ in their biological activity and the extent to which they can penetrate the skin. The shorter the wavelength, the more harmful the UV radiation. However, shorter wavelength UV radiation is less able to penetrate the skin.

UVC can range from 100 to 280 nm and is blocked out by the ozone layer.

About UVB Radiation
UVB radiation ranges from 280 to 320 nm, and it mainly penetrates the superficial skin layers, i.e., the epidermis. UVB radiation is the major cause of sunburn, which is acute skin damage perceived as redness. Additionally, it has been identified as a leading factor in the development of skin cancer. The immediate result of UVB radiation is skin redness and thickening of the SC, which is a defense reaction of the body to reduce the UVB effect on the epidermis. The redness ad potential pain subsides in a relatively short amount of time; however, the underlying damage accumulates over time.

This leads to the formation of various types of skin cancer. Additionally, UVB contributes to photoaging and tanning and also has immunosuppressive effects. An advantageous effect of UVB radiation is that it is responsible for the synthesis of vitamin D in the skin. 

The intensity of the UVB varies by season, location, and time of day. The most significant amount of UVB is experienced between 10 AM and 4 PM during late spring and early summer. However, UVB can burn and damage the skin all year, especially at high altitudes and on reflective surfaces such as snow or ice. UVB rays do not significantly penetrate glass.

About UVA Radiation
UVA radiation ranges from 320 to 400 nm. Due to their longer wavelength, UVA rays penetrate into the skin, down to the dermis. These rays can be further subdivided into UVA II (320 to 340 nm) and UVA I (340-400 nm). 

In the short term, UVA radiation leads to skin tanning (i.e., browning), which is often considered a sign of health. It is unfortunate since tanning, whether outdoor or indoor tanning, causes cumulative damage over time, leading to photoaging.

UVA has long been identified as a leading factor in photoaging; however, until recently, it was not believed to cause any cancer. Studies over the past decades, however, show that UVA damages keratinocytes in the basal cell layer where most skin cancers occur. Therefore, in the long term, it can also contribute to and may even initiate the formation of skin cancer. 

Additionally, UVA weakens the immune system, which also helps the development of skin cancer. Photosensitivity reactions are also primarily mediated by UVA. Tanning beds primarily emit UVA radiation, and the lamps used in tanning salons can emit doses of UVA up to 12 times that of the sun.

Therefore, indoor tanning is associated with a significantly increased risk of skin cancer, and the risk is higher with use in early life (<25 years). It should be kept in mind that UVA radiation retains the same energy level all day long, every day of the year. Therefore, it has the same damaging effect in the morning as in the late afternoon and during winter as during summer. Additionally, it can penetrate window glass. These fats underline the importance of protection against UVA light.

Facts You Should Know

• To make it simple to remember the difference between UVA and UVB, think of "A" (UVA) standing for aging and "B" (UVB) standing for burning. Both UV radiations can cause skin cancer.
• UVC radiation is recognized as the most carcinogenic. fortunately, almost all UVC radiation approaching earth is filtered out by the protective ozone layer. The only source of UVC on the surface of the earth is germicidal lamps, which are used to kill germs on surfaces or in the air.