You asked

Why is my five to eight year old child picking his nose?

While nose-picking isn’t one of the greatest source of worry for parents aside from being socially unacceptable and unhygienic, it is a good idea to try and nip this unsavoury behaviour as soon as possible.One of the biggest concerns about nose-picking is that germs on the fingers can lead to small skin infections inside the nose. Fingers that have been in a nose may enable the spread of colds and flus.
Kids who pick their nose frequently tend to be children who have allergies. The heavy flow of mucus and the way it crusts gives them a ‘something’ up there feeling.
Remedying dehydration or congestion is the best way to stop nose picking. It’s also a good idea to teach your child the importance of using a tissue instead of using fingers.
In addition, try these tactics:
Check his allergies: At this age, a stuffy nose could be caused by allergies, the most common of which are dust mites, animal dander, pollen and moulds.
Keep him hydrated: If the weather is dry or more likely, if the central heating seems to be drying out your child’s nasal passages, try increasing the amount of water and other fluids he drinks during the day and consider placing a humidifier in his bedroom at night. 
Get him into the habit of washing his hands: Children won’t automatically wash their hands all the time, but try to get them into the habit of washing them a few times a day, before meals and after trips to the bathroom and also if they have been playing outside.
 Ignore it: If you have done all of the above and your child still occasionally picks his nose, your best bet us is to keep his fingernails short and do your best to ignore it. Like most bad behaviour, he will grow out of it. 

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