According to the Human Interface Guidelines, a touch target should be no smaller than 44×44 points. But a UIBarButtonItem, which many common action such as navigation rely on, is only about 20×20 points.
Is there any reason for this (other than the fact that these are ‘guidelines’)? Will my app be rejected if I use a similar sized button where I feel it is appropriate?
The touch area of a UIBarButtonItem is much bigger than the size of the icon. So it is not violating the HIG.
Your app is not likely to get rejected if you have a button with a touch area that is smaller than 44×44 but it will be harder for a user to use. I’ve used plenty of apps with tiny touch areas. Make it bigger if you can, don’t when you can’t.