According to the hindus, every creature ( including the plants) has an aura, an invisible emanation surrounding him. This aura is the result of the past thoughts, actions and karma. Touching someone who has depressive thoughts can badly affect your own aura. Therefore, people who belong to untouchable castes have to be avoided by persons of an higher status: touching them would bring bad karma, it would affect their aura too. In the contrary, the aura is benefitted if a person with powerful positive thoughts is touched.
Moreover, hugging and embracing among the two sexes is dangerous, even for spiritual masters, because even them could fall under the power of sexual attraction. Affection can be expressed by other ways than physical touch.
Hindus believe also that the fingertips are one point through which the powerful aura can be discharged. That is the reason why, when spiritual masters bless someone, they bless him by touching the topmost point of the head, where there is a powerful centre called “sahasrara”, a “chakra” that if awakened lead to spiritual realization.