In Thailand, the head is regarded as the highest part of the body, both literally and figuratively. It is the ‘home of the soul and the spirit’ and must be given respect. Thus, Thai people are careful not to touch the head and hair of other people.
Touching someone's head is taboo – it is taken as an insult, a serious lack of manners. Only parents, grandparents and other senior relatives can touch the heads of their small children or grandchildren. When the children grow up even that is no longer allowed. Sons and daughters do not touch their parents’ heads.
In social gatherings, young Thais try to keep their heads lower than those of their elders, and you should avoid passing things over people’s heads.
If you touch someone’s head by mistake, you should apologise immediately.