The basic concept of sunscreen as the name suggests sunscreen means a shield from the sun or before the sun, basically it protects from the sun to be harmed the skin from the ultraviolet radiation it is basically of two type UVA and UVB that can cause many problems. It may be also called as sunburn cream, sun Protection, sunblock...
What a sunscreen do, it does not matter whether it is a cream, lotion, spray or a gel all works on a same principle which is it absorbs or reflect some of the sun's UV radiation (ultraviolet rays) therefore helps to prevent the skin from sunburn or sun tan.
Sun protection factor, is a meter of sunscreen ability to prevent UVB from damaging or destroying the skin, what SPF do it take 20 min for unprotected skin of getting red,by an SPF 15 sunscreen deeply prevents burning 15 times longer it works about to five hours.
The SPF scale:
In other word we can say this that SPF15 will work 4% less than SPF 30
Firstly we need to know what is a PA in sunscreen it is just a rating system used to indicate the UVA protection it is a Japanese measurement of sun protection. The PA system is mostly found in Asian products.PA is a protecting level of strength to mark the three PA+,PA++ and PA+++.
Most preferred sunscreen are sunscreen with SPF 30 and SPF 15 because sunscreen with more higher SPF for example SPF 75 and SPF 100 do not have that much greater ability to protect from UV rays as compared with SPF30 and as well as it's also misleading the people into thinking that they are totally protected, but they actually not. To have broad spectrum prevention UVA protection must be 1/3 of the UVB protection. Sunscreen with high SPF mostly offer far greater UVB than UVA, thus having wrong exception of having high protection.
There are certain step one needed to follow for getting better response these are as follows: