The choice of sunscreen should be based on the use environment. Students generally have less outdoor time, so they choose SPF 15.

How to choose sunscreen:

First, see through the sun protection index: SPF

SPF value is the main content marked on every bottle of sunscreen. The true meaning of SPF value seems too formal to understand. Scientific SPF refers to the ratio of the energy required to produce the minimum erythema on the skin protected by sunscreen to the energy required to produce the same degree of erythema on the skin without any protection. Simply put, it is the time multiple of skin's resistance to ultraviolet rays.

For the yellow race, it is calculated as follows: generally, the skin of the yellow race can resist sunlight 15 minutes without being sunburned, so using SPF 15 anti-ultraviolet products will have a sunscreen time of about 225 minutes. Theoretically, the level of sun protection index reflects the ultraviolet protection ability of sun protection products. The higher the SPF index, the greater the protection, but the increase of SPF value is not proportional to the ability to shield ultraviolet rays.

Generally speaking, products with the lowest SPF 2 ~ 6, medium SPF2~6 ~ 8, high SPF6~8 ~ 12 and SPF value of 12 ~ 20 are high-intensity sunscreen products, and products with SPF value of 20 ~ 30 are ultra-high-intensity sunscreen products. However, there are many people who like to bask in the sun abroad, so the index of sunscreen products designed is relatively high, and some even reach SPF80.

Second, see through the sun protection index: PA

The effective protection time of PA+ is about 4 hours. The effective protection time of PA++ is about 8 hours. PA+++ super protection. It has been scientifically confirmed that UVA- 1 is the killer of skin aging, so Japanese scientists have developed a sunscreen that specifically resists UVA- 1 and used "+"to indicate the defense strength. The correct term for PA is protection.

UVA- 1, and its degrees are marked with+,++and++. The more "+",the better the anti-UVA effect.

If you carefully observe the sunscreen products on the market now, you will find that many sunscreens not only have SPF value, but also have clearly marked PA value. Because SPF is aimed at UVB ultraviolet rays, that is to say, it can only defend the total amount of ultraviolet rays on the ground 1%, but it can't do anything about the real sunshine killer UVA. Therefore, sunscreen products for UVA will play a more effective role. Products marked with PA have such a function, which can reach the bottom of dermis in the shortest time and prevent ultraviolet rays from damaging elastic fibers and causing skin aging.

Usually, the strength of PA is represented by+,and one more+means that the effective protection time is prolonged. Specifically, the effective protection time of PA+ is about 4 hours. The effective protection time of PA++ is about 8 hours. PA+++ super protection.

Third, how to choose the appropriate SPF value

1. For people with normal skin, the SPF value should be 8 ~12;

2. For people who are sensitive to light, the SPF value is12-20;

3. Sensitive skin should choose sunscreen formulated by plants or physical sunscreen containing titanium dioxide.

4. For office workers who only bask in the sun on their way to and from work, the SPF value can be below 15, mainly for face sun protection;

5. When playing in the wild and swimming by the sea, the SPF value of sunscreen products should be above 30. It is best to choose waterproof and sunscreen skin care products when swimming.

Fourth, sunscreen products should choose PA value.

It is not enough to look at SPF value for sun protection today. Because SPF can only defend against U-VB ultraviolet rays, that is to say, it can only defend against 1% ultraviolet rays. The real sunshine killer is U-VA, which accounts for 98% of ultraviolet rays on the ground. UVA is the most lethal, because it can reach the bottom of dermis in the shortest time, quickly damage elastic fibers and cause skin aging. The only way to deal with UVA is to choose "PA+" products to prevent UVA. Because of the reflection of the sun's light, the skin in water will absorb twice the ultraviolet rays. So you should not only choose SPF30 or above, but also choose PA+++ sunscreen, and it is best to choose sunscreen milk instead of sunscreen. If you go to the seaside in summer, you should choose something with a higher sun protection index.