At least in the Brahmin households, still the practice of not touching anything and anyone after having haircut until taking bath is followed. What is the reason for this? Any scriptural reference?
For the time being I'm only able to cite something relevant from the "Neeti Shastras" (NS) by Chanakya. This book is of course not a scripture.
But in the 1st Chapter only the author says:
I recite maxims of the science of political ethics (niti) selected from the various sastras (scriptures)
- That man who by the study of these maxims from the sastras acquires a knowledge of the most celebrated principles of duty, and understands what ought and what ought not to be followed, and what is good and what is bad, is most excellent.
So, the maxims found in the book are said to be from one scripture or the other.
Now, after certain acts like a hair cut or a shave or nail cut or an oil massage or intercourse etc the body is considered as impure. So, a bath is ordained.
From NS 8.5:
- After having rubbed oil on the body, after encountering the smoke from a funeral pyre, after sexual intercourse, and after being shaved, one remains a chandala until he bathes
Although the verse explicitly does not mention hair cut but it applies to hair cut as well.
As regards, why one is not allowed to touch things, then that's because they consider the impurity to be mobile i.e. transferable. That is, the belief that an impure person can make other things impure by his touch.