I have been wondering about this complement for a long time. If you have been to Japan, or if you watch Japanese variety shows, you may hear this comment made on somebody’s physical appearance; “His/Her face is so small!!!!” or more frankly, “Kao Chissa!!” [顔ちっさ] which is a casual way of saying that you have a small head, which makes you look like thin, beautiful, and admirable like a model.
I do not watch other mainstream media in East Asia, so I do not know if there is any similar admirations going on in any other countries other than Japan. I have just never heard this phrase, “You have a small head” in any English speaking countries that I have been. If you have someone tells you this in English, wouldn’t that sound more like… your brain is too small to be smart or something?
I guess in Japan, there is a big admiration of having a good body proportion. When put a ruler right next to your head, if the length of your head is 1/9 of your whole body length, that makes your body look like a model. (Of course, you have to be super thin on top of that, in order to meet the conventional image of beauty in Japan.) So, let’s say if you are 182 cm (6 ft) tall, then your head length should be around 20 cm (8 in). So it is better to be born tall in the first place. And not many East Asian people get to be that tall.
In general, there are too many jokes made on people’s physical appearances in Japanese entertainment industry. For example, your face is too large, your chin is too long, your beard hair is too thick, and what have you. You may see that kind of comments made amongst Japanese stand-up comedians, and this type of comments are called kao-ijiri [顔いじり]. Not sure this atmosphere coincides with many people’s desires to permanently remove their hairs from their bodies (including men’s beard hair) or for cosmetic surgeries to have larger eyes and smaller chin bones. I am not saying there must be a causation. At least, making laugh out of one’s physical appearance is seen as childish and immature in the cultures that I am more familiar with, both in Japan and the North America. So I think this is not ill-minded as it may sounds to some people. Ijiri [いじり] can be just the expression of teasing, but yeah, there may only be a thin line between that from bullying and self-hatred.
So imagine yourself visiting Japan and having a conversation with local people. If you were told “you have a small face,” just take it as a complement. That would be one of those bit weird and potentially interesting cultural differences that you may expect while traveling abroad.