I. Overview
1, ultraviolet radiation in nature is produced by solar radiation, its spectral wavelength is 180-400nm, due to the different biological effects of ultraviolet light and divided into three wavelengths, respectively, short-wave ultraviolet (UVC180-290nm), medium-wave ultraviolet (UVB290-320nm), long-wave ultraviolet (UVA320-400nm).
2, in nature, wavelengths shorter than 290nm can be absorbed and scattered by the air, clouds, dust, water and other atmospheric layers, so the atmosphere can filter out the short-wave ultraviolet (UVC).
3.UVC is scattered components are more, even in the shade there is a large number of ultraviolet radiation.
4, due to human activities leading to environmental pollution, a large number of ozone layer is being severely damaged, the daylight in the ultraviolet radiation reaching the surface of the earth more and more damage to humans, skin is no exception.
Second, classification
1.Physical sunscreen
2.Chemical sunscreen
3.Physical-chemical sunscreen
Three, the difference between physical sunscreen and chemical sunscreen
1, the principle of UV protection is different. The former is through the reflection and scattering effect to achieve the prevention of ultraviolet radiation, the latter is through the absorption of ultraviolet rays in the sun and play a role.
2, safety: generally speaking, the former is safer than the latter. Therefore, the former can be used for extremely sensitive skin and skin that is sensitive to chemical sunscreens.
3, texture: in general, the former texture is not as good as the latter.
Fourth, the role
1.To absorb or block UV rays.
2.Reduce the damage of UV rays on the skin.
V. Ingredients
1, sunscreen active ingredients include inorganic and organic compounds, mostly particulate metal oxides, such as zinc oxide and titanium dioxide, with the function of protection against UVA and VVB.
2, in recent years the use of nanoscale zinc oxide and titanium dioxide powder as a sunscreen, such products have good transparency, will not produce powder opaque and white appearance, and chemically inert, safer.
VI. Applications
1, photosensitive skin diseases: polymorphic sun rash, solar dermatitis, chronic actinic dermatitis, hormone-dependent dermatitis, facial reoccurrence dermatitis, etc.
2.Sun aggravated skin diseases: lupus erythematosus, dermatomyositis, chloasma, freckles, rosacea, etc.
3.New skin after laser photon treatment, chemical peeling treatment and various cosmetic techniques.
4.Anti-cancer: such as actinic keratosis, basal cell carcinoma, seborrheic keratosis (i.e. age spots), etc.
5.Anti-sunburn.
6, anti-photoaging.
Seven, sunscreen efficacy evaluation methods
1.The determination of SPF value
Is the sunscreen agent to protect the skin to prevent the occurrence of sun erythema index, because sun erythema is mainly UVB-induced skin phototoxic reaction.
Therefore, SPF value represents the indicator of UVB protection effect.
Minimal Erythema (MED) refers to the appearance of clearly identifiable erythema (border) on the irradiated area after 16 to 24 hours of UVB exposure.
The minimum amount of UV radiation energy required for the appearance of clearly identifiable erythema (clear boundary and reach the edge of the irradiation point).
2.Measurement of PFA value
①PFA is the indicator of sunscreen to protect the skin from tanning, because tanning is mainly UVA-induced skin photo-oxidation reaction, so the PFA value represents the indicator of the protective effect of UVA.
②Minimum sustained pigment darkening (MPPD) generally refers to the minimum amount of UV radiation energy required for slight pigment darkening at the irradiated site within 2 to 4 hours after UV irradiation.
PA (Protection of UVA) represents the level of protection against UVA, according to the size of the measured PFA value to indicate different PA levels.
PA (Protection of UVA) represents the level of protection against UVA.
PFA value < 2 No UVA protection
2< PFA value < 3 PA +
4< PFA value <7 PA ++< p>
PFA value > or = 8 PA +++
VIII. Summary
For non-professionals, in the process of choosing sunscreen, it is only necessary to be clear about the following points.
1, SPF value represents the indicator of the effectiveness of protection against UVB, that is, to prevent the skin from turning red. In a year, the summer medium-wave ultraviolet rays (UVB) are the most abundant and intense, so you should choose a higher value of SPF, generally SPF>30.
2, PA value represents the indicator of the effectiveness of protection against UVA, that is, the indicator of preventing skin darkening. Long-wave ultraviolet rays (UVA) are present throughout the year, so the choice of sunscreen must not ignore the PA value.
3, a complete and appropriate sunscreen must have SPF and PA value two indicators.
4, face sensitive skin, be sure to choose a physical sunscreen, or better yet, a medicine.
5, some people think that the SPF value is too high for the skin is damaged, in fact, it is not, because the SPF value only represents the ability to prevent the skin from turning red after UV exposure, so in the summer should choose a sunscreen with a higher SPF value, other seasons can be lower.
Nine, discuss
What is the difference between sunscreen, barrier cream and BB cream?
X. Tips
Those who have read my article suggest to make an evaluation whether it has practical value for themselves.