Spitting upon another person, especially onto the face, is a global sign of anger, hatred, disrespect or contempt and it is a degrading thing.
In children spitting is an aggressive form of behaviour and It can result from children trying to handle stress, an expression of anger, a bid for negative attention or a means of defense.
What ever the reason for the spitting, it cannot be good enough to excuse the behaviour and it is a habit that you do not want your child to develop.
Spitting must be stopped as soon as it is started.
Babies and toddlers tend to spit a bit and they usually grow out of it, but as the child grows he might spit to get a negative reaction from you. By not reacting, you tell your child that his spitting is not impressive and you can use the opportunity to show him that it is unacceptable behavior and that it doesn't give him what he wants.
You can insist that the child cleans the spit and in a calm and controlled manner make him apologize and let him know how dirty it is to spit. If your child refuses, consider discipline, such as a removal of privileges. Give him a towel and explain to him that spitting spreads germs and let him know what it means to spit on some one.
Teach your child verbal and healthy ways to react and display his emotions. Explain that spitting is never good, but other methods, like talking about his feelings or letting an adult know can help him express anger in a more constructive way. Model positive methods of dealing with anger and sadness to provide your child with a good example.
Explore alternative reasons for the spitting. If your child doesn't seem to be spitting when dealing with emotions like anger, sadness and fear, his spitting could actually be a form of obsessive compulsive disorder (OCD).
If you think that OCD can be the reason, you need to seek professional help. Speak to your doctor and ask him for advice.