The most likely diagnosis is a sebaceous cyst
. This is not serious. It is a cyst that can enlarge and become inflamed. They are common on the scalp
. They contain a whitish material that can ooze out. They may become inflamed or infected in which case they can weep a bit and feel painful.
I would suggest a visit to your doctor, but this does not need to be urgent. Your doctor will then be able to advise you on whether it may be worth getting it removed. This would be a minor procedure which can sometimes be carried out under local anaesthesia.
Dr K A Pottinger