I think Carang's idea is a good one. My usually smiley, lovely baby, started getting stranger anxiety at about 7 months. Most unlike him, he would cry whenever anybody new talked to him. This started just before we went on a holiday with 14 relatives who he didn't really know and I was dreading he would be upset the whole time, but you know, when he was immersed into this situation with so many new faces he got over the anxiety really quickly and has been fine ever since. More exposure helps I think.