This question was originally posted in quora and was answered by: Prarthana Bhat, medical student The answer to this question lies in the deep deep ANATOMY of the nose The nose is divided into two halves by the nasal septum. At the antero-inferior angle of the nasal septum, four arteries of the nose form something called an 'anastomoses' which in simple terms means, that four different arteries which supply blood to the nose join together and form a 'network' . This network of arteries is called the Kiesselbach's plexus. SO, when you 'PICK YOUR NOSE' : Your finger is coming in contact with this arterial network which is carrying blood to your nose. And most of the time, you damage it causing the arteries to leak which you experience as a nose bleed. And like what the above users said, you are also transmitting germs to your nasal passages and in turn respiratory tract. In addition, there is a rare possibility of the spread of infection from the area between the nose and upper lip ( medically called 'dangerous area of the face') to a part of the brain called the 'cavernous sinus'. But, this is extremely rare. So, yes it definitely BAD for you. For those who are further interested, the names of the four arteries are: Anterior ethmoidal artery Sphenopalatine artery Greater palatine artery Septal branch of superior labial artery Source
