For example, when the UV index for a particular day reports that a particular skin type can remain exposed to the sun without sun screen for 10 minutes, it means that during the 11th minute the skin will begin to burn. However, if an SPF15 sun screen has been applied before sun exposure, the skin will be protected for 15 times longer from UV radiation – in this case the skin will be protected for 150 minutes (10min x SPF15 = 150min), before it begins to burn on the 151st minute.
Therefore an SPF15 sun screen extends the period for which the skin is safe sun exposure from 10 minutes to 150 minutes. By applying HIMAYA SPF30 sun screen the skin will not burn until after 300 minutes, and so on.[ 10 (min) x 30 (SPF) = 300 minutes
Calculating the SPF with environmental variables
The UV Index is calculated every day, based at sea level. Environmental factors such as snow, water and altitude greatly affect the UV Index. Because of its reflective properties, snow will almost double the level of sun exposure, therefore the safe period of time in the sun will be halved.
For instance, if the UV Index specifies that without sun screen protection a particular skin type can safely remain in the sun for 10 minutes, on the snow it will be half of that, or five minutes. For skin to be exposed to the sun for more than five minutes, sun screen protection is necessary to avoid damaging the skin.
Altitude is another factor affecting the UV Index, again shortening the time of safe sun exposure. At an altitude of 3000m, sun exposure is double that at sea level. Therefore the duration for safe sun exposure is halved.
To continue with the above example, sun exposure at 3000m, in combination with snow, will reduce your safe sun exposure time to approximately two-and-a-half minutes:[ 10 (min) x 50% (altitude) x 50% (snow) = 2.5 minutes ] This is why in the mountains and other places where UV radiation can be reflected, a hat is not enough. To fully protect the skin from dangerous UV radiation you must also apply very strong sun screen protection or total sun block.
It is important to understand that applying two sun screens with different SPF values does not give an SPF value of the sum total. The SPF will simply be that of the higher number.
For example, applying an SPF15 and an SPF30 does not give a protection of SPF45. It simply gives the sun protection of the stronger of the two, in this case SPF30.
Applying more sun screen protection does not extend the time of safe sun exposure.
Most sun screen manufacturers recommend reapplying sun screen often. This is because their products are easily sweated away of rinsed off by water.
It is important to note that reapplying the same sun screen does not increase the SPF value, or the safe sun exposure time. Reapplying SPF15 throughout the day will not extend the safe sun exposure time beyond 15 times the applicable UV Index for a particular Skin Type.
HIMAYA’s exclusive Sports Formula sun screen, on the other hand, maintains 100% of its SPF despite sweating or prolonged time in the water. Therefore it is not as important to reapply HIMAYA as often as other leading sunscreens.