What does the PA plus sign and the SPF number in sunscreen mean? Which one is better?

The degree of sun protection of sunscreen can be seen from the index on the bottle. You can see the confidence that you can choose the one that suits you. What do the plus sign and number of sunscreen PA mean? Which one is better, SPF15, SPF30 or SPF50?

What does the plus sign and number on sunscreen PA mean?

PA stands for sun protection index. The more plus signs it has, the higher the sun protection index is. One plus sign means an SPF of 15, which provides protection for 150 minutes; two plus signs mean an SPF of 25, which provides protection for 250 minutes; and three plus signs mean an SPF of 30, which provides protection for 300 minutes.

Which is better, SPF15, SPF30 or SPF50?

SPF is the abbreviation of Sun protection factor, which means sun protection index. The higher the sun protection index of cosmetics, the stronger the sun protection ability. The "sun protection" here can generally only prevent sunburn, but not tanning. Some studies have shown that East Asian skin types will produce erythema in an average of 15 minutes, so an SPF sunscreen product uses SPF1 as the smallest unit, which means it can block ultraviolet rays for 15 minutes in the sun. SPF15 can block ultraviolet rays for 15*15=225 minutes, or 3 hours and 15 minutes. SPF30 can block ultraviolet rays for 15*30=450 minutes, or more than 7 hours! And SPF50 is 50*15=750, which means it can block ultraviolet rays for 12.5 hours without taking any protective measures.

This theoretical deduction seems feasible, but in reality it is subject to many factors, which makes it unable to provide protection for such a long time. Due to different UV intensities and different personal skin types, the time it takes for you to develop erythema after sun exposure may not be 15 minutes, and it may be shorter than 15 minutes. If the amount of product used is insufficient or the method of use is improper, coupled with factors such as sweating, the sunscreen film will be damaged and the sun protection ability of the original product will be greatly affected.