In 1978 the American Food and Drug Association (FDA) adopted SPF (sun protection factor) as UVB sun protection efficacy criterion. SPF expresses how long you can stay under the sun without burning. The point to be considered here is the intensity of sunlight. In other words, the amount of sunlight, not the duration of exposure, is important. When we consider the weather conditions that are likely to cause burns in 10 minutes, for example, when the sun’s rays are inclined and the humidity is low, it means that it provides protection for 15×10 minutes = 150 minutes. In other words, we can say that you can stay out in the open without burning for 1 hour at nine o’clock in the morning, but only 10 minutes at one o’clock in the afternoon.
Factors such as skin type, amount of sunscreen application, humidity in the air, amount of activity (increases in physical activity) affect the protection factor.
To briefly summarise, SPF does not reflect the time in terms of how long to stay under the sun, it allows it to compare the level of sunburn protection provided by different sunscreens.
SPF is mostly a marker for UVB rays, a standard protection factor has not yet been determined against UVA rays. UVA rays are responsible for ageing and reach deep tissues and cause cellular damage. In formulations that provide both UVB and UVA protection, the term broad spectrum is used in addition to the SPF value.
Broad spectrum sunscreen formulations contain mineral and chemical filters. The use of vitamins known as antioxidants in addition to the sun filters creates a barrier effect against free radical formation caused by UVA rays, reaching the lower levels of the skin. For this purpose, vitamin C and E are used.
In a good sunscreen formulation, it is important that all these ingredients attach to the most damaged upper layer of the skin.
The silk protein has the same structure as keratin tissue, which consists of 18 amino acids, and clings to the upper layer of the epidermis. Here, silk proteins form a thin but very strong barrier and prevent UV rays from reaching the lower layers of the skin. At the same time, the effect of the formulation creates an equal amount of protection on the surface of the skin by increasing the homogenisation.
In the use of silk protein with physical filters, it has been determined that it provides effective UVA as well as homogeneous UVB protection. Silk protein, which has a strong UV retaining feature as a very important filtration agent is included in Therasilk ® sunscreen and with its special formulation, takes its place among the new generation of sunscreens.