Avobenzone or Butyl Methoxydibenzoylmethane (Parsol 1789)
(Photostability issue)
คำชี้แจงส่วนตัวของผู้รวบรวม
เรื่องของ avobenzone นั้น เป็นเรื่องที่ถกเถียงกันว่ามันเสถียรหรือไม่กันแน่ ถ้าใครลองอ่านงานวิจัยก็จะพบคำตอบที่ทำให้ปวดหัวหนักไปกว่าเดิม เพราะว่าแม้กระทั่งเอกสารของ USFDA เองก็ยังออกมาสนับสนุนว่าใช้ได้ แต่ก็ออกมาบอกว่าสารที่ใช้ป้องกันยูวีเอนั้นไ่ม่มีความคงที่และสามารถเสื่อมสภาพได้ เล่นเอาผู้อ่านงงกันไปตามๆกัน
ทุกคนที่่เข้ามาอ่านเรื่องนี้คงทราบกันอยู่แล้วว่า นอกจากรังสียูวีเอนั้นจะทำให้ผิวเข้มขึ้นแล้ว ก็ยังมีผลต่อผิวหนังชั้น dermis ทำให้ผิวเหี่ยวย่นก่อนวัยอันควร และทำให้เป็นมะเร็งผิวหนังได้ในระยะยาว
ดังนั้นเพื่อความปลอดภัยของผิวทั้งหน้าและตัว....ดิฉันจึงอยากจะสงสัยเอาไว้ก่อนเชื่อตามงานวิจัย ที่บอกว่ามันไม่เสถียร เมื่อโดนแดดไปสามสิบนาที หรือ หนึ่งชั่วโมงก็จะหมดสภาพ ......ทั้งนี้ทั้งนั้นเพื่อความปลอดภัยของตัวเอง......ไม่อยากเอาตัวเองไปเสี่ยงในเมื่อมันไม่จำเป็นน่ะค่ะ ดังนั้นความเชื่อส่วนตัวของดิฉันเองก็คือว่า.....ถ้ามันไม่ได้ใส่สารที่ทำหน้าที่ stabilizer มาด้วย ดิฉันขอสงสัยไว้ก่อน......ดีกว่าต้องมานั่งเสียใจภายหลังน่ะค่ะ
"Avobenzone provides superior protection through a large portion of the UV-A range, including UV-A I. It has been widely used in Europe for the last decade. The FDA recently approved avobenzone for use in the United States. Potentially a significant addition to sunscreen products for true broad-spectrum UV protection, concerns have been raised regarding its photostability and its potential to degrade other sunscreen ingredients in products in which it is used. " (Stanley B Levy, MD, Clinical Professor, Department of Dermatology, University of North Carolina at Chapel Hill)
There have been many articles printed and discussions concerning photostability. This is an issue that must be addressed. A product designed to protect a user should of course do so and not significantly degrade altering the absorption characteristics during the UVR exposure. There have been statements made that photostability is not a problem in that the SPF test shows that the product is protective for the amount of time labeled. This is a true statement, but is misleading. Most of the photostability discussed are in relation to UVA filters. What TRLI has found is that some products even though not photostable, still exhibit little change in SPF, and in fact sometimes increase in SPF as the UVA protection degrades. This is due to the fact that the protection degrades in the UVA region, but actually increases in the UVB region (UVB protection = SPF Value, added by editor), thus in some cases actually increasing in SPF value while steadily decreasing in UVA protection
United States Food and Drug Administration. Department of Health and Human Service. March 28,2002
*TRLI = Tanning Research Laboratories, Inc.
More from USFDA 1998 regarding Photostability of sunscreen ingredient
Photostability or how to prevent UV rays from degrading sunscreens?
(information from Ombrelle Lab)
Ultraviolet rays have the capacity to degrade some ingredients in solar filters, and considerably diminish their efficacy. This is not the case with physical screens, which are photostable. Generally, filters that assure UVB protection resist solar energy well through absorption and reflection.
It's different for UVA filters. Some of them, and Parsol 1789 (avobenzone) in particular, degrade quickly in the sun (1). Researchers have reported a 36% reduction in UVA absorption by Parsol 1789 (avobenzone) after only 15 minutes of exposure (2). In vitro studies have shown a 50% loss in UVA blockage for different sunscreen formulations, confirming the photodegradation of Parsol 1789 (avobenzone) (3-5).
To counter this phenomenon, some formulas use the indicator, "photostable" which means they do not degrade in the sun. To date, recognized active ingredients that stabilize Parsol 1789 in sunscreens are:
The methods for avoiding photodegradation include the use of photoresistant molecules or the transfer of energy captured by UVA filters to another molecule. The molecules vibrate, causing a mechanical rotation and re-emittance of the energy in the form of infrared (IR) photons. This energy causes no molecular damage (8).
Avobenzone (Parsol 1789) vs. Microfine Zinc Oxide
by Sheldon R. Pinnell, MD and Doren L. Madey, PhD (May/June 1999) New and Improved Daily Photoprotection. Aesthetic Surgery Journal, the peer-reviewed journal of the American Society for Aesthetic Plastic Surgery
Avobenzone, also known as Parsol 1789, is a chemical sunscreen agent that is absorbed through the epidermis. Although it blocks long-wave UVA, it does not block UVB or short-wave UVA radiation, and must be combined with other sunscreen ingredients to yield a "broad-spectrum" product. One recently published in vitro study shows that avobenzone degrades in the presence of sunlight and is rendered ineffective within just 1 hour. Avobenzone also has been shown to degrade other sunscreen ingredients, with which it is combined, including the most common UVB ingredient, OMC, and a common short UVA block, oxybenzone.
Zinc oxide is the closest thing to a total sunblock on the market today. It uniformly covers from 290 to 380 nm, thus protecting against UVB and most of the UVA spectrum. No other sunscreen ingredient provides broader protection. And unlike many chemical sunscreen agents, zinc oxide is never irritating. In fact, it is recognized by the Food and Drug Administration as a Category I skin protectant, meaning that it is safe for compromised or environmentally challenged skin. Zinc oxide has over a 300-year history of safety, with no known adverse reactions (which is why it is often used to treat babies). Now, in its microfine form, it is ideal for use in sunscreens and daily moisturizers.
Are all broad-spectrum sunscreens equally effective?
They're all pretty good at screening UVB rays, but blocking UVA is a little trickier. Don't rely on products that contain avobenzone (also called Parsol 1789) if you're spending the day at the beach. Studies have shown that this ingredient can break down after only half an hour of exposure to UVA and may even degrade chemicals in the lotion that screen out UVB. The most effective sunblocks contain zinc oxide or titanium dioxide. Unlike chemical sunscreens that sink into the skin and absorb radiation as it hits, these ingredients sit on top of your skin, forming an almost invisible physical barrier against UV rays. All sun protection products will lose their effectiveness after a while, so check the expiration date before using them. If you have any doubts about how old the tube is, buy a new one.
Photostabilization of butyl methoxydibenzoylmethane (Avobenzone) and ethylhexyl methoxycinnamate by bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), a new UV broadband filter
It is now well documented that chronic UVA exposure induces damage to human skin. Therefore, modern sunscreens should not only provide protection from both UVB and UVA radiation but also maintain this protection during the entire period of exposure to the sun. UVA filters, however, are rare and not sufficiently photostable. We investigated the effect of the introduction of a new UV filter, bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), in oil in water sunscreen formulations on the photostability of butyl methoxydibenzoylmethane (Avobenzone [AVB]) after irradiation with an optically filtered Xenon arc source (UV irradiance adjusted at 1 mean effective dose [MED]/min). With spectrophotometrical methods to assess the sun protection factor (SPF) and UVA ratio and chromatographical methods to determine the amount of UV filters recovered after irradiation we showed that Tinosorb S prevented the photodegradation of AVB in a concentration-dependent way, leading to a sustained SPF and UVA ratio even after irradiation with doses of up to 30 MED. Since AVB was shown to destabilize ethylhexyl methoxycinnamate (EHM) we tested the effect of Tinosorb S in sunscreens containing this UV filter combination. Here too Tinosorb S showed photoprotective properties toward both UV filters. Thus, Tinosorb S can be used successfully to improve the photostability and efficiency of sunscreens containing AVB and EHM.
Chatelain E, Gabard B. (2001). Photostabilization of butyl methoxydibenzoylmethane (Avobenzone) and ethylhexyl methoxycinnamate by bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), a new UV broadband filter. Photochrmistry and Photobiology, 74 (3): 401-406.
Photoallergic contact dermatitis
แล้วทำไมเค้าไม่ใส่ stabilizer ซะให้มันหมดเรื่องไป เฮ้อ.....บางทีก็แพ้น่ะสิคะ ลองอ่านนี่ดู
In a 71-year-old male Caucasian patient with persistent eczema on light-exposed skin, photocontact allergy was demonstrated to the UV filter substances 4-methylbenzylidene camphor (UVB) (stabilizer), octyl methoxycinnamate (UVB), benzophenone-3 (UVA) and butyl methoxydibenzoylmethane (UVA) (another name for avobenzone)present in sunscreen products used by the patient over several years. A significantly reduced UVB sensitivity of 25 mJ/cm2 in this patient (normal minimal erythema dose in our laboratory = 70-130 mJ/cm2) was considered an early indication of a persistent light reaction. Topical anti-inflammatory treatment over 2 weeks together with consequent application of a sunscreen containing Mexoryl SX/titanium dioxide led to complete remission. Taking into account the widespread use of the above UV filter substances not only in sun protection products, but also in cosmetics such as antiaging lotions and day care products, the possible risk of allergy to these chemicals has to be taken seriously. The substitution of known photocontact sensitizers in UV filters by photostable compounds and detailed product information are the basis of preventive strategies.
Schmidt T., Ring J. and Abeck D.(1998) Photoallergic contact dermatitis due to combined UVB (4-methylbenzylidene camphor/octyl methoxycinnamate) and UVA (benzophenone-3/butyl methoxydibenzoylmethane) absorber sensitization. Dermatology. 196(3):354-7.
อ่านรายงานการวิจัยที่เกี่ยวกับความเสถียรของสารป้องกันรังสียูวีเอ
in vivo = ทดสอบในคนหรือว่าในสิ่งมีชีวิตจริงๆ in a living organism
in vitro = ทดสอบในห้องแลป หรือว่าในสถานการณ์จำลองที่เหมือนจริง artificial environment