The first time I saw this happen I was very confused. My thai mother picked up her grandson, put her nose up to his cheek, and deeply inhaled before telling him “hom makk,” or you smell good. I was even more surprised when I came home from a trip and my mother put her nose against my cheek, as I realized, self-consciously, that she was smelling me.
This seems funny to me since Thailand is such a hot climate. People are always sweaty, so why would you want to intentionally smell each other?? Thai people do love their powder, though, so usually its not too bad. No bath is complete without caking copious amount of powder on, usually with bleach in it to lighten your skin and something in it to give you a cooling sensation. Most nights after my nephew takes a bath and his face looks like he has a mask on from the amount of powder on his face, everyone asks “hom mai?” and smell him, to show their affection. In a way smelling instead of kissing makes sense though. Pheromones play a large part in how we relate to others, and maybe Thai people are more aware of this natural instinct.
In general though, Thailand is not a touchy place. I never see couples holding hands, hugging, and definitely never see kissing. During my time living with two different families, first with a married couple in their 40s during my training, and now with a married couple in their late 20s, I have never once seen them kiss. Even in the privacy of their own home. Maybe this lack of intimacy is partly due to the hot, sticky, climate, but most of it is likely due to the Buddhist ideal of non-attachment. Not to be too attached to objects, or people, of this world. I respect and admire this, but definitely miss a big hug once in a while!