The sun emits UV (Ultraviolet) light that reaches the earth, partly penetrates the Ozone layer of the earth and reaches the earth’s surface. All UV light is invisible for the human eye but has a high lever of energy. If it reaches the surface of the earth it can cause a (chemical) reaction.
There are 3 types of UV light. UVA, UVB, and UVC. They are distinguished by the wavelengths of the light.
UVA has a wavelength of 320-400 nanometer (nm), UVB has a wavelength of 290-320 nm, and UVC has a wavelength of 200-290 nm. The shorter the wavelength, the higher the energy of the light and so the more damage it can do. But the longer the wavelength the deeper the light penetrates into the skin. Exposure to UVC would destroy our skin and fortunately this UV light is completely absorbed by the gases in the earth’s atmosphere (among others by the Ozone layer) and does not reach the surface of the earth. UVA and UVB penetrate the atmosphere relatively easily and even on cloudy days they reach us.
UV light (especially UVB) is necessary for most of the synthesis of Vitamin D in our body. People that have no exposure to UV light whatsoever can develop a Vitamin D deficiency with negative consequences for, among others, bone development.
UV light also causes the natural pigmentation in the skin (especially UVA) that protects against sunburn caused by further exposure to the sun.
Some skin conditions like Psoriasis can have beneficial results from exposure to UV light.
Most effects of UV light on the human skin are seen as negative. UV light causes skin cancer, premature aging and wrinkling of the skin, and sunburn (up to severe second degree burns). Traditionally UVB has been held responsible for redness, sunburn, skin cancer and DNA damage in the skin after exposure to sunlight. It has a shorter wavelength than UVA, has a higher energy level and causes more damage.
UVA has a longer wavelength and lower energy level (but penetrates deeper into the skin), and it has been seen as the UV light that causes the pigment reaction of the skin to UV light (Tanning).
Sunscreens are rated with a Sun Protection Factor (SPF) number, a number that primarily reflects the sunscreen's protection from UVB. SPF numbers are calculated by dividing the MED (Minimal Erythema Dose, defined as the minimum UVB exposure required) with the use of a sunscreen applied by the MED without sunscreen.
In other words: If it takes in Aruba on a Sunny day for a specific person to get the first redness after 10 minutes of sun exposure on the unprotected skin and 20 minutes for the skin protected by a specific sunscreen then the SPF of that sunscreen is 2 (20 divided by 10). Note because of this way of calculating an SPF of 8 does not double the amount of UVB that is filtered out. As examples: An SPF 2 filters 50% of UVB, and SPF 8 filters 87.5%, and SPF 16 filters 93.6%, and SPF 32 filters 96.9% and an SPF 64 filters 98.4%. You can also apply SPF to clothing. The protection afforded by a light-colored cotton shirt is equivalent to an SPF of only 10.
SPF is a relative number so it is not depending on the location, weather at that location or the skin of the person tested. A sunscreen product with an SPF 2 will have this SPF 2 in Aruba but also in Miami and for all persons that use the product.
Notably is that the MED is measured based upon redness of the skin that is caused as a result of exposure to UVB only and so the MED nor the SPF gives an indication of protection against UVA.
By using certain ingredients the sunscreen products can be made water resistant. The definition of water resistant is that the product will retain its sun protective effect even after swimming or perspiring. Caution should be taken when using water resistant sunscreens because a false feeling of safety may cause the user to stay too long in the sun. Even with water resistant sunscreens it is important to re-apply the sunscreen regularly especially after swimming or exercise.
It is now internationally recommended by the regulating agencies to use an application thickness is 2mg of cream per square cm of skin. A more useful measure is for an average size adult to use 1 fluid ounce (30 ml) per whole body application. This does not sound like a lot but it is far more than what the average sunbather is using currently. Even water resistant sunscreens must be reapplied after swimming or heavy sweating.
The FDA considers that sunscreens are Over The Counter (OTC) drugs. This means they are considered drugs but they are freely available for the public. This causes the FDA to demand that producers and distributors of these products abide to the FDA rules concerning drugs. All Aruba Aloe sunscreens are registered at the FDA and the labeling of the products is subjected to strict specifications and proposed rules.
