I don't have particularly small ears, they fit pretty comfortably, but as I'm finding out my ear opening is quite small. When I used the ear buds that came with my mp3 player they kept falling out, I couldn't get them to fit in my ears. So Mac loaned me his foam head phones, which were nice, soft, but the sound wasn't as good---I had to turn the mp3 player all the way up-- and they didn't fit very tightly, guess I have a small head too.
So yesterday Mac picked me up a pair of ear buds that had 3 different heads to go on them and told me to try the medium. Couldn't get it in my ear, so small it was. So far they're working fine, but I forgot to turn the sound down o the mp3 player and when I first turned it on I about blew out my ear drums. Today was better.