You're in the car driving your four year old to dance class. You sneak a peek of her in the rear view mirror and you're horrified to find her vigorously picking her nose. You find it disgusting and gross and hope she's not picking in public. You decide to ignore it hoping she will stop on her own.
Two weeks later she's still picking her nose and you can't take it anymore. You start nagging and threatening punishment if she doesn't stop but that doesn't seem to be effective. What can you do?
The first thing I suggest is investigating whether it's related to the season. Winter months and dry indoor air can lead to excess mucus, dry nasal membranes, etc. She might get the feeling that "something's up there" so she picks. Perhaps a saline nasal spray or a humidifier would be helpful. Keeping her fingernails short and snag-free can be a deterrent to nose picking.
Also take into consideration what's going on when she is picking her nose. She might be bored, curious or trying to get your attention. Try keeping her fingers busy with a squishy ball, a finger puppet, or bandages on the tip of her finger especially when you're out in public where you don't want to have to be correcting her. Same goes for when you're at home. Give her something to do with her hands rather than telling her not to pick her nose.
Nose picking is unsettling but most kids try it at some point. As a parent try not to let it get to you and approach resolving it in a calm manner.