Mexoryl可以说是这个夏天最热门的防晒成分了。简单的说mexoryl是一种有很好的photostable的UVA filter, 一般分为两种Mexoryl SX 和 Mexoryl XL, 前者是水溶性的，后者是油溶性的，所以前者一般加在粉底，或者保湿乳液里面，而后者就用在防水的防晒品。photostability的意思就是 it doesn't degrade significantly when exposed to light。而另外一种UVA filter Avobenzone却不是photostable的，所以在expose在阳光下5小时左右就会失效，需要 frequent reapplication.
下面这几段摘抄还挺有用的，大家如果想了解这种成份不妨看看：
Ecamsule (USAN, trade name Mexoryl® SX, INCI Terephthalylidene Dicamphor Sulfonic Acid) is a chemical which is added to many sunscreens to filter out UVA rays. It is a benzylidene camphor derivative, many of which are known for their excellent photostability.[1]
Although there are a few different UV absorbers with the trade name Mexoryl, only two of them are widely used where approved. Mexoryl SX (water soluble) and Mexoryl XL (INCI Drometrizole Trisiloxane, oil soluble). Together they show a synergistic effect in protection.[2] The patents are held by L’Oréal. Sunscreens containing ecamsule are exclusive to L’Oréal and its brands.
Exposed to UV, ecamsule undergoes reversible photoisomerization, followed by photoexcitation. The absorbed UV is then released as thermal energy, without penetrating the skin.
UVB rays cause short-term sunburn and skin cancer; UVA rays cause wrinkling and may have some role in development of skin cancer. There is no official rating for UVA protection in the US. In Europe, there are several different rating systems that are used to measure effectiveness in blocking UVA rays, including the IPD (immediate pigment darkening assay) and the PPD (persistent pigment darkening assay). The UVB range is 280 to 320 nanometers, and the UVA range is 320 to 400. Ecamsule protects against UV wavelengths in the 290–400 nanometer range, with peak protection at 345 nm.[3][4] Since ecamsule doesn't cover the entire UV spectrum, it should be combined with other active sunscreen agents to ensure broad-spectrum UV protection. Ecamsule is a photostable organic UVA absorber, meaning it doesn't degrade significantly when exposed to light. This is in contrast to the widely used UVA absorber avobenzone that is not intrinsically photostable and requires photostabilizers to prevent significant degradation in light.[5][6][7]
Q What is the difference between Mexoryl SX and Mexoryl XL?
A Let's answer this question by first analyzing the ingredient mexoryl and then discussing the two forms available on the international market for sun protection. Mexoryl is the new sunscreen active popular in Europe and South America, which has not been approved for use in the United States. Nevertheless, many high-end pharmacies, spas, dermatologists and Internet drug services are selling mexoryl-containing sunscreens supposedly illegally in this country. Mexoryl, originally developed by scientists working for L'Oreal to stabilize avobenzone, is also known as Parsol 1789. Avobenzone is an excellent broad-spectrum photoprotectant that was developed by Roche, however, it is somewhat photo unstable. Meaning that the avobenzone degrades rapidly when exposed to UVA radiation increasing the need for frequent reapplication.
One molecule of avobenzone can absorb UVA radiation only once, making it inactive from that time forward as opposed to zinc oxide or titanium dioxide that can reflect UVA radiation over and over again with minimal decay. All of the avobenzone applied to the skin is virtually rendered inactive after five hours of UVA exposure.
Mexoryl effectively extends the life of avobenzone and two formulations were developed. Mexoryl SX is a water-soluble form that is suitable for day wear sunscreen formulations. This would include sunscreen-containing moisturizers and facial foundations. Mexoryl XL is an oil soluble form that is suitable for water-resistant sunscreen formulations, including those worn on the beach and during vigorous physical exercise.
