像是为什么上面没有PA的标示，或者是为什么产品里本来就含有UVA的防晒成分，但包装上并没有UVA的防晒标示。

 

首先因为PA标示是日本的标准，美国并没有规定采用，所以产品上没有标示PA值是很正常的

 

至于第二点其实美国在先前对于UVA的防护标示是有建议可以标示"Broad spectrum"(宽带防护)

 

其详细定义如下:

 

The UVR absorbance spectrum of the preparation was measured, and the critical wavelength was computed using the method of Diffey. According to Diffey, the critical wavelength is the wavelength below which 90% of the area under the absorbance curve resides, and a critical wavelength of 370 nm or greater defines a "broad spectrum" sunscreen.

 

(The critical wavelength standard is difficult to understand. The higher the the critical wavelength of a sunscreen, the better its UVA-performance in relation to its UVB-performance. The critical wavelength is given as the upper limit of the spectral range from 290 nm on, within which 90% of the area under the extinction curve of the whole UV-range between 290 nm and 400 nm is covered. The Critical Wavelength method  requires mathematical integration of the in vitro product absorbance spectrum from 290 to 400 nm to determine the wavelength below which 90 percent of the cumulative area of the absorbance curve resides. )

 

简单说也就是临界波长于370nm以上才能称为Broad spectrum

 

但这样的定义对于消费者来说实在很难理解，计算上也不是相当容易，所以FDA一直想在UVA防晒标示这部分订定新标准。

 

1999年就开始计划一直到了2007年才定稿

最后它没有直接采用日本的PA值或欧系的PPD值

也放弃只有简单标示Broad spectrum的做法

而采用"星号评比制"(共有1-4星的强度差异)

这样的新规定可谓是近年来FDA对于防晒标示的重大突破

而以皮肤科医师的观点来看真的是乐观其成

 

 

(1)FDA对于UVA的防护重视由此可见一斑

(2)FDA对于UVA的防护测试同时考虑了体外及体内测试

(PA值及PPD值是体内测试;Critical wavelength是体外测试)