Relationship between ultraviolet intensity and weather conditions in Kunming

Kunming is located in Yunnan-Guizhou Plateau, where ultraviolet rays are generally strong.

Actually, the weather in Kunming is very good. Otherwise, how can you get the reputation of spring city? Generally, it is no problem to wear sunscreen or skin care when going out. It's no problem to bring an umbrella.

First of all, you should know about ultraviolet rays.

Ultraviolet rays are divided into UVB and UVA.

The harm and protection of UVB have been thoroughly studied. It can make skin sunburn and redness in a short time (about 25 minutes for ordinary people). At present, most sunscreen products on the market are UVB type, and SPF is a symbol of UVB protection ability.

UVA is a terrible sunshine killer. UVA has a long wavelength and strong penetration ability, which can penetrate the skin surface and penetrate deep into the tissues below dermis, and can destroy the fine structures inside the skin, such as collagen and elastic fiber tissues, produce wrinkles and fine lines, and make the skin slack and aging. This is medically called photoaging.

In the energy distribution of ultraviolet rays in sunlight, UVA is 15 times that of UVB, which is the main cause of skin tanning. It can reduce the hyaluronic acid content of the combined water in the skin, make the skin dry, accelerate the formation of melanin, and make the skin black, which is also an important cause of skin cancer.

It is found that the skin will appear relatively stable blackening after about 2-4 hours of UVA irradiation with normal intensity, which is called "continuous instantaneous blackening" academically.

The so-called SPF value refers to the product's ability to protect against UVB, that is, the ability to prevent skin sunburn. Generally speaking, it takes 20-25 minutes for human skin to produce erythema under direct sunlight. If the SPF value of a bottle of sunscreen lotion is 8, it can protect the skin for about 20 (25) × 8 = 160 (200) minutes once. For details, please refer to the following table:

SPF value use condition

2-8 sunshine in winter, sunshine and rainy days in spring and autumn.

9-20 Summer Morning and Evening and Moderate Intensity Sunshine

21-30 outdoor work, tourism and strong sunshine in summer

Exposure to strong sunlight in a specific environment (such as plateau) with a temperature greater than 30℃.

In foreign countries, in addition to SPF value, the word "PA+" can often be seen on the packaging of sunscreen products that pay attention to UVA, which indicates the protective ability of products against UVA, that is, to prevent tanning. Generally, the products with this logo are just sunscreen products with advanced technology. At present, there are no products in China. The PA value represents the following meanings:

PA value effective protection time

PA+ about 4 hours

PA++ about 8 hours

PA+++ super protection