The emphasis in fashion photography does not lie on the garments, but on the mood and styling of the image. The garments are merely an accessory to convey a certain lifestyle. Therefore, the whole image is much more complex. You usually won't see plain white or off-white backgrounds in fashion photography and the models are usually styled very dramatically with thick eyeliners, dramatic eye shadows, etc. With the increased complexity in styling also comes an increased complexity in lighting to make the image look more dramatic. Here's some fabulous examples:
Commercial fashion photography predominantly sells a product. Hence, the emphasis of the whole shoot is on the product. That means that the lighting, the styling, and the background are usually very plain (not in a bad way). Think of catalog shoots where the models is standing in front of a white or an off-white background with maybe one light above camera and slightly to either side of the camera, and very natural looking make-up. Here's some great examples:
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