Trend of UV absorber technology for cosmetics

The ultraviolet spectrum in sunlight is in the range of 100 to 400 nm, and can be divided into three bands, 100 to 290 nm short-wave ultraviolet (UVC), 290 to 320 nm, ultraviolet (UVB) and 320 to 400 nm long-wave ultraviolet (UVA).

Figure 1: The wavelength and name of the sunlight

When UVC passes through the atmosphere, it is mostly absorbed by the ozone layer and cannot reach the surface of the earth.

UVB is about 290-320 nm long, most of which is absorbed by the epidermis, and a small part reaches the superficial layer of the dermis, which is the main band of skin damage. It can directly act on the skin layer, causing immediate and serious skin damage, such as erythema, sunburn, etc., while accelerating the production of melanin. Although UVB penetration is not as good as UVA, it is excessively exposed to the skin and is prone to skin cancer. Therefore, UVB is also called UV Burn.

A small part of UVA is absorbed by the epidermis and most of it can penetrate into the dermis and reach the middle of the dermis. UVA has a wavelength of 320-400 nm and is active in the air all year round. It reaches the surface of the earth at noon in summer and is 100 times more than UVB. It is highly permeable and can attack the dermis layer or even the subcutaneous tissue through the wall or glass, causing the collagen fibers in the skin to break and lose its elasticity, causing irreversible damage to the deep structure of the skin, thereby accelerating skin aging and activating prolinease. Accelerate melanin production, ie photoaging and immediate pigmentation, which eventually lead to premature aging of the skin, causing long-term, chronic and long-lasting damage, so UVA is also known as UA Aging. Sunscreen products must be chosen to protect against UVA and UVB.

Figure 2: Schematic diagram of UV penetration capability in different bands

The familiar sun protection factor (SPF) is mainly used to evaluate the UVB resistance of sunscreen products. It is usually followed by a number after SPF, which represents the unprotected skin sunscreen time after using sunscreen products. The skin began to burn after 20 minutes without any sun protection. However, after applying SPF15 sunscreen products, the skin protection time of the product is 20X15=300 minutes under the same conditions, the skin is burnt after 300 minutes.

The SPF value determines how long the skin can withstand the sun, not the intensity of the UV light. The following formula can quickly give an approximate sunscreen effect:

Formula: (SPFxx-1) SPFxx X100%

Example: (SPF15-1) SPF15 X100%=(15-1)/15=93.33%

According to the above results: SPF15 can resist more than 93% of UV rays and SPF30 is only about 3% more than it, not twice. At the same time, products with high SPF value will increase the burden on the skin. The sun protection factor of SPF15 can meet the needs of working and living sun protection on weekdays.

At the same time, PA (Protection Grade of UVA) was released in 1996 by the Japan Cosmetic Industry Federation to identify UVA sunscreen efficacy standards. In recent years, with more and more manufacturers cited, consumers gradually began to accept and agree with this new sunscreen index. It is different from SPF. It is not a number behind the PA, but a "+" sign. The more "+" behind it, the stronger the effect of resisting UVA. The highest sun protection factor on the market is "PA+++".

The PA value is based on the PFA result:

PFA = MPPD value applied to the sunscreen part / MPPD value without the sunscreen part PFA (Protection Factor of UVA): Ultraviolet UVA factor (MPD): minimum tanning dose

The first level: PFA1-2 (excluding 2), represents the effect of not having UVA protection, no PA value;

The second level: PFA2-4 (excluding 4), represents the effect of protective UVA, equal to "PA+";

The third level: PFA4-8 (excluding 8), represents the effect of strong protection UVA, equal to "PA++";

The fourth level: PFA>8, representing the effect of very strong protection UVA, equal to "PA+++"

In other words, suppose our skin is sunburned after sun exposure for 1 hour without any sun protection, and the PA++ product is applied. Under the same circumstances, the skin will be tanned after 4-8 hours. Phenomenon, it can be seen that moisturizing products containing PA++ sunscreen ingredients are enough for daily life.

In addition, sunscreen ingredients are generally classified into chemical (including UV absorbers) and physical (including UV barriers).

1. Chemical sunscreen ingredients (including UV absorbers)

Sunscreens are often found in sunscreen skin care products. At present, it is mainly composed of a chemically synthesized ultraviolet absorber, which absorbs ultraviolet rays. The ultraviolet absorber is absorbed by the skin tissue and then metabolized by the human body. Specifically, the chemical components in the sunscreen enter the skin keratin and after absorption through the skin, interact with the ultraviolet rays to transform them into harmless energy. Because it is a chemical reaction on the skin, it has some stimulation to the skin. In particular, it is easy to cause problems such as roughening the skin and irritating the eyes. Moreover, the ultraviolet absorber itself is a photosensitive substance, which may cause irritation to the skin and cause a photosensitivity reaction.

2. Physical sunscreen ingredients (including UV shielding agent)

It usually stays on the surface of the skin and is not absorbed or metabolized by the body. Specifically, it refers to the use of particles in sunscreens to block, reflect or scatter ultraviolet light, thereby reducing the amount of ultraviolet light reaching the skin. Because it does not chemically react, it is mild to the skin. The shortcoming of the ultraviolet shielding agent is that the transparency is poor, and the finished product is coated on the skin like a layer of hoarfrost. In addition, their use is not subject to any restrictions in the country and can be used to make products with very high SPF values.