I have been through scalp acne and I can tell you it causes such uneasiness and such discomfort that you wish to go bald. It is always the best thing to go to a doctor. When you see the whole area has been infected, you have to immediately go for a professional help.
In medical terms the condition is called as the Scalp Folliculitis. Scalp acne can happen for various reasons. This is an allergy that occurs in the scalp and it can happen from the hair products that are used. This acne can be referred to the genetic conditions also. You can also change the conditioner that you have been using for the scalp.
Have you heard of the apple tree oil? Well I got to hear of it very recently when I read it has been a prescribed medicine over the years on acne and also to prevent the future breakouts and infection of acne. There are some hair products that have the extract of the Green Tree which is a medicated shampoo as well as a natural alternative.
And in spite of all your precautions if you are still facing the problem, you have to see a doctor immediately. To get rid of the scarring washing with coconut water or applying calamine would help. You could be started on antibiotics in the form of medicines or the topical cream. You can use some prescription medicine or the cream for that purpose.