Views: 2 Author: Site Editor Publish Time: 2022-07-18 Origin: Site
Basics of UVA and UVB
There are only two kinds of ultraviolet rays that can penetrate the ozone layer and reach our skin, UVA and UVB, of which UVA is the main (there is also a kind of UVC, which is dissipated in the process of penetrating ozone).
UVB has a short wavelength and UVA has a long wavelength. Therefore, UVB energy is large, and it mainly destroys the epidermis, but UVB consumes almost the same amount of UVB through the epidermis, and not much can reach the dermis. And UVA not only destroys the epidermis, but also easily reaches the dermis to continue to destroy.
Consequences of destruction of the epidermis (caused by both UVA and UVB): sunburn, sunburn, tanning (melanin is synthesized in the bottom layer of the epidermis), and skin cancer - most skin cancers occur in the epidermis, such as those with high mortality rates Melanoma (the cells that produce melanin become cancerous).
UVB mainly causes sunburn, and induces skin cancer; UVA mainly causes tanning, which can also induce skin cancer.
Consequences of damage to the dermis (mainly caused by UVA): premature aging of the skin - the reason why the skin can be so elastic is because of the support of collagen in the dermis, and excessive UVA will damage the cells that produce collagen and affect collagen protein synthesis, which causes premature skin aging and wrinkles.
Therefore, sunscreen must prevent both UVA and UVB, otherwise it is an incomplete sunscreen. However, UVA is further subdivided into UVA1 and UVA2 due to the relatively wide band and it is difficult to cover with a single sunscreen ingredient.
Scientific name "butylmethoxydibenzoylmethane.
It's one of the few ingredients that protects against UVA1 well (though it only protects against UVA1, so it must be used in combination with other sunscreen ingredients).
A bottle of sunscreen, if it does not contain avobenzone, zinc oxide, and bis-ethylhexyloxyphenol methoxyphenyl triazine, is basically not a competent full-band sunscreen, because it can These three ingredients are effective against UVA1.
Chemical sunscreens. Oil soluble.
One thing that is often criticized is: poor photostability. In its defense: it's true that pure avobenzone loses nearly 40% of its effect in one hour of exposure to sunlight, which is certainly not acceptable - very frequent wipes, and too short a shelf life.
But just add a little light stabilizer, and more conveniently, other sunscreen ingredients can act as its light stabilizer. For example, octocrylene, such as bis-ethylhexyloxyphenol methoxyphenyl triazine, and some moisturizing and moisturizing ingredients are also its light stabilizers.
Another point that is often criticized is: strong skin irritation. Possibly more irritating than glycerin, but it is indeed permitted and widely used. So, instead of blindly assuming that avobenzone will cause allergies, try it first, such as on your hands and neck.
2. Zinc Oxide
One of only two physical sunscreens, safe, natural, non-toxic, harmless and non-irritating.
At the same time, it is one of the very few three-band full defense components.
Zinc oxide and titanium dioxide are both white powders, and their principle is equivalent to coating the face with white pigment to reflect ultraviolet rays.
Although the current technology is very advanced, the zinc oxide and titanium dioxide are micronized to the nanometer level (< 100 nm), and the surface treatment has greatly reduced the problem of white face, but if the content is high, it will still be white. .
Purely relying on zinc oxide or titanium dioxide, if you want to achieve a higher SPF, you have to apply it thicker, and if you want to apply it thickly, the texture is usually sticky, which is the same as sticking briquettes.
Those who need to remove makeup are usually pure physical or physical-based sunscreens, because the oil is relatively heavy, and it is not easy to wash off with ordinary face wash.
3. Titanium Dioxide
In addition to zinc oxide, another physical sunscreen, the same safe, natural, non-toxic, harmless and non-irritating.
The EU introduced a new regulation in 2009, all sunscreens must have a UVA:UVB protection ratio of at least 1:3, which is intended to enforce the protection against UVA. In other words, if a bottle of sunscreen has 10% UVA protection and 90% UVB protection, it is not qualified.
Not as broad spectrum as zinc oxide. Titanium dioxide only protects against UVB and UVA2, and is less effective against UVA1.
Specially anti-UVB. widely used.
Chemical sunscreens. Oil soluble.
Homosalate can affect hormone levels in the body. A bit out of context: in vitro experiments, homosalate showed estrogen-like and androgen-suppressing properties; but in vivo experiments, in mice, homosalate had no effect on hormone levels. It is allowed in all countries as long as the concentration does not exceed the limit (10% in the EU).
Some people say that it is unstable when exposed to light, so the shelf life is not long, and if it is not used up within 1 year, it has to be thrown away. It is true that homosalate is not the most stable sunscreen, but it also has a shelf life of 2-3 years.
Another one for UVB protection. It is also widely used. For example, in the Nivea series mentioned above, the second sunscreen ingredient is octocrylene.
Chemical sunscreen, oil soluble.
Not easy to cause allergies, good photostability.
6. Bis-ethylhexyloxyphenol methoxyphenyl triazine
(Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine)
Broad spectrum, all three bands can absorb
good light stability
Oil-soluble and water-soluble versions are available
Safer, unlike homosalate, this ingredient has been shown to be safe even in vitro.
Scientific name "benzophenone-3".
Chemical sunscreens. Both UVA2 and UVB resistant. But not UVA1 proof.
In addition to two physical sunscreens, zinc oxide and titanium dioxide, and broad-spectrum chemical sunscreens, bis-ethylhexyloxyphenol methoxyphenyl triazine, there are only benzophenones that can protect against both UVA2 and UVB.
Benzophenone is not only used in skin care products, but also in industry, such as adding to plastics to prevent plastics from aging due to ultraviolet rays.