How to calculate the sun protection index? What is the best sun protection index for sunscreen?

Sun protection is extremely important in summer. If you don’t do a good job of sun protection, you will get dark instantly when you go out. How do you calculate the sun protection index? What is a good SPF?

How to calculate the sun protection index

The SPF value applies to everyone. Assuming that the intensity of ultraviolet rays does not change with time, an East Asian skin type will produce erythema after an average of 15 minutes of sun exposure. According to theoretical calculations, when using SPF15 sunscreen, it means that the time can be extended by 15 times, that is, it will take 225 minutes for the skin to get sunburned; when using SPF30 sunscreen, it means that the time can be extended by 30 times, that is, it will take 450 minutes for the skin to get sunburned. The calculation method is 15 times SPF, which equals the sun protection time.

What is the best sunscreen SPF?

There is no best value for the sun protection index, but only a most suitable value. Not only the place of use should be appropriate, but also the people who use it should be appropriate. Generally speaking, if you work indoors and don't go out much, you should use sunscreen with an SPF of SPF15 to SPF20; if you need to travel outside for work or during holidays, you should use sunscreen with an SPF of SPF20 or above; if you travel to a beach or tropical area, you should use sunscreen with an SPF of SPF30 or above.

During daily commuting, the sunscreen you use should depend on your skin color. People with fair skin are best to choose sunscreen with an SPF of SPF30 or above to prevent the formation of spots, while people with darker skin can choose sunscreen with an SPF of SPF15. In addition, people who are sensitive to light should also choose sunscreen with a relatively high SPF.

How to choose the right SPF value

There are two types of sunscreens: UV absorbers and UV shielding agents (such as ultrafine powders of titanium dioxide and zinc oxide). It is impossible to have an SPF of 20 or above without titanium dioxide. While absorbing ultraviolet rays, sunscreen has a certain irritating effect on the skin. If the ultraviolet absorber is excessive, it will become a burden on the skin. Therefore, the choice of sunscreen should be determined based on your workplace, time and sunlight intensity.