July 2, 2021 Longchang Chemical

The summer is scorching, and many places across the country are very hot and hot. As a chemical practitioner, of course, you must take a rigorous attitude towards sun protection. Then how to choose sunscreen?

First of all, why do you need sun protection under a little science? The reason is that there are ultraviolet rays in sunlight. Ultraviolet rays are the general term for radiation with wavelengths from 100nm to 400nm in the electromagnetic spectrum, which cannot cause people’s vision. Simply put, it is in the sun, but you can’t see it. Ultraviolet rays can cause damage to the skin, especially the dermis. Ultraviolet rays are generally divided into three categories according to different wavelengths, UVA, UVB, and UVC.

Short-wave ultraviolet UVC: It is ultraviolet light with a wavelength of 100~280 nm. UVC is the most harmful to organisms. However, this thing is absorbed in the ozone layer… and it is easily blocked… so it is OK without any protection.

Medium-wave ultraviolet UVB: It is ultraviolet light with a wavelength of 280~320 nm. Ultraviolet rays in the medium wave have certain physiological effects on human skin. It acts more on the epidermis. Due to its higher order energy, it can cause strong light damage to the skin. The dermal blood vessels of the irradiated area are dilated, and the skin may have symptoms such as swelling and blisters. Long-term exposure to the skin will cause erythema, inflammation, and skin aging (Just sunburn). Therefore, UVB is also called the sunburn (red) section of ultraviolet rays, which is the ultraviolet band that should be prevented.

Long-wave ultraviolet UVA: It is ultraviolet light with a wavelength of 320~400 nm, which is subdivided into UVA-1 and UVA-2. The penetration of long-wave ultraviolet rays on clothing and human skin is much stronger than that of medium-wave ultraviolet rays. It can reach deep in the dermis and can act on the melanin in the epidermis, causing skin melanin deposition, darkening the skin, and protecting against ultraviolet rays. Protect the skin. Therefore, the long-wave ultraviolet is also called the “tanning section.”

It can be seen that to prevent skin damage caused by ultraviolet radiation to the human body is mainly to prevent ultraviolet UVB radiation; and to prevent UVA is to avoid skin tanning.

So in order to prevent the world from being destroyed and the skin from being harmed by ultraviolet rays, people invented sunscreen. Everyone should have noticed the SPF (Sun Protection Factor) factor on sunscreen. How did this coefficient come from? For example, after a person is exposed to the sun for 20 minutes, the skin starts to redness and erythema appears, and after applying sunscreen, the time becomes 10 hours (600 minutes), then the SPF of this sunscreen product is 10 hours/20 Minutes=30, which is actually a multiple of the shortest sunburn time, so… the sunscreen effect is still related to your personal physique… If you get sunburn in just 1 minute–, please allow me to make a sad expression. .. (Science students always feel that this kind of experiment is too accurate = =)

There is also an index on sunscreen called PA, generally PA+, PA++, PA+++, this is the ability of sunscreen to prevent sunburn. But the definition is still very vague…that is, it can prevent tanning, effectively prevent tanning, and…very effectively prevent tanning.

Since UV is actually prevented, we can directly use UV-Vis spectrophotometry to determine whether the sunscreen is effective or not! Okay, okay, it’s actually just use a beam of light to take a photo, and then see how much it is absorbed. The more absorbed, the less it reaches the skin, and the better the sunscreen effect!

1. Weigh the sunscreen to the nearest 0.0001g

2. Dilute with water, mix well with ultrasound, add water 1000 times (mL) of the weighed mass (g)

3. 4500μL water+500μL diluent

4. Toot toot, vortex and shake, and mix well

5. Pipette cell, use this to measure absorbance, first measure the background

6. U-3010, UV-vis. Put it in! scanning! Obtain the spectrum.

This spectrum…look at it this way…the horizontal axis is the wavelength, and the vertical axis is the absorbance. Simply put, between 280~400nm on the horizontal axis, the higher the line, the better the sunscreen effect! Between 280~320nm is the absorption capacity of UVB, that is, the ability to sunburn, and between 320~400nm is the absorption capacity of UVA. Because the concentration configured above is the same! So you can paste all the tested brands in a picture for comparison, so you get the OTZ spectrum of this picture.

A total of 9 samples were tested this time, namely… Dior (I think it’s like a liquid foundation), Vichy, and L’Oreal Paris (two types, the white and blue bottles are different in color), Affordable Materia Medica, Mentholatum, skinfood, as well as the big treasures that you see every day and the Internet hottest water baby… The following is the result:

Dior, the principle of big-name freedom, is far ahead of UVB protection, that is, it can extend sunburn for a longer time, but it is not so good in UVA protection, but it surpasses other brands~ but it is really expensive. !

Vichy, the performance is very good, the protection of UVA is in place, it can effectively prevent tanning, and the absorption of UVB is also very good. It is very good for normal use.

The two sunscreens of L’Oréal Paris also perform well, with even absorption. The 340~380 bands, which generally do not perform well in other sunscreens, still have higher absorption, providing more bands of protection, and at the same time, the absorption of UVB is also sufficient.

Mentholatum’s sunscreen performs well in UVB, but it is not particularly ideal in terms of UVA protection, and… can I complain about it, is it particularly like a correction fluid…?

Suitable herbal sunscreens are relatively smooth in the full range of absorption, but they are not outstanding, normal sunscreens.

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