According to American and British physiologists, this very bad habit of which parents always try to cure their children turns out to be very healthy. The question is, that mucous membrane of human nose has many receptors. Stimulating them could influence different functions of human organism.
For example, in this way brain activity could be stimulated. This is probably why many people, while thinking over some difficult problems, start picking nose. Moreover, picking nose could help to faster get rid of grippe and usual influenza. Stimulating receptors situated in nose helps to the organism to more actively fight with the illness.
This, of course, does not mean that this habit is now considered to be decent. It is still improper to pick nose in a company. Though, somewhere all alone… Why not to strength your health?