Eversince I’ve been back in Thailand, I keep getting comments on how I don’t look “Thai.” My parents are both Thai, so how can I not look Thai? Alex is also commented to not look “Thai” either. Some of my friends who have lived abroad most of their lives, also get the same comment.
When people look at my friends and I who spent a lot of time abroad and were not born and raised entirely in Thailand, they can tell almost right away even without having had a conversation.
I’ve been thinking about this for years now and together with my observations of friends’ facial features, I’ve come up with a theory of my own: People’s facial features, depending upon where they grew up, form differently as a result of different muscle usage.
Why? People in the US and Europe use different kind of facial expressions from those in Asia. Upon observation, I think that my friends who grew up in the US with both Thai parents seem to have somewhat bigger jaw muscles and cheeks.
I think this is due to the way we use our muscles when we speak. When speaking English and Thai, different muscle usage is required. We also have different kind of facial expressions. Europeans and Americans use expressions that require more movement of their eyes and forehead. Most asians and Thais (who grew up in Thailand), on the other hand, are not so expressive with their face. Foreheads are hardly used, and are thus not wrinkled as much. Smiles are more common.
Overtime, our muscles on our face form according to how we use them. Therefore Thais, who were born and raised in a different language and environment, end up with certain facial features that make them standout from Thais who were born and raised in Thailand. Of course, it will have to be a substantial amount of time, probably during your formative years, to allow time for your muscles to develop.
Okay, so that’s my theory on why people who grew up outside their native country look different. What do you think ??
Having "Me" Time 
I was searching for some site on facial features of thai when I stumbled on your page. It is a pretty interesting theory that you have mentioned here. I have a Chinese friend who can differentiate between Chinese and Singaporeans by looking at the face almost instantly. I have often wondered what exactly strikes the eye when deciphering one’s origin.
And by the way, looking at your display pic on top right, you do look Thai to me (assuming it’s you in the pic). But again, I am not a Thai so don’t possess that incisive insight into recognizing Thais from non-Thais.