Clothes and vanity sizing

Is this something you have become aware of? I have always been small but I can no longer buy size S. It seems I now need XS. I have not lost weight. A size 8 would have been right for me a few years ago but is now too big. Is the reason for this vanity sizing to make people feel better and does it work? The problem people like me have is that it isn't easy to find size XS or size 6 in shops.