Headache also known as cephalalgia is a medical condition characterized by pain in any part of the head and neck area. Usually headache occurs as a presenting symptom of an underlying health condition.
Brain itself does not produce any pain as it lacks pain sensing receptors, however there are structures around the brain which are the main source of pain. These include the inner lining of the bony skull (periosteum), muscles, nerve tissue, blood vessels including the arteries and the veins, mucosal lining etc.
Management of the underlying cause is the mainstay of treatment, however, pain killers are used for symptomatic relief.
Symptoms
Headache can affect one or both the sides of the head. Based on the intesity of the pain, headache can be throbbing, dull or sharp in character. Sometimes headache may appear gradually over days and may also last for few days. In some cases headache can be associated with vomiting, light intolerance (photophobia) etc. depending upon the underlying cause.
Causes
There are about 200 different types of headache depending upon the underlying cause. Typical characters of the symptoms along with certain investigations are helpful in diagnosis of the underlying causes.
There are mainly two types of headache; these are primary and secondary.
Primary headache occurs whenever the pain sensitive structures around the brain tissue are affected. Usually interplay of different chemicals secreted in and around the brain tissue plays an important role in primary headache. Sometimes the affected persons are genetically prone to suffer from headache.  
Common types of primary headache include cluster headache, migraine, tension headache, trrigeminla autonomic neuralgia. There are other less common varieties of primary headache which have special characters. These include cough headache, sex headache, exercise headache etc. Primary type  of headache can be precipitated by certain change in the lifestyle; these are chronic heavy alcoholism, maintaining poor posture, stress, skipping the breakfast etc.
Secondary headaches occur following problems in the head and neck area. Common causes of secondary headaches include meningitis characterized by inflammatory changes in the meninges, the protective cover of the brain and spinal cord, bleeding in the brain, brain tumor, abnormal swelling of the arterial wall (aneurysm) leading to increased pressure on the adjacent structures in the brain, acute attack of closed angle glaucoma, acute sinusitis, dehydration etc.
In some type of secondary headache there are no underlying problems rather exposure to specific conditions may trigger headache. These conditions include eating ice creams (ice cream headaches or brain freeze), chronic use of pressure causing head gears (external compression headache), intake of certain pain killers (rebound headache) etc.
Treatment
Treatment of headaches depends upon the type and the underlying cause (if any) of the headache. The approach of treatment includes relief of symptoms and management of the underlying cause.
Relief of symptoms can be achieved by intake of pain killers like aspirin, Tylenol, etc. Triptans are prescribed to relieve pain, especially in people suffering from migraine, ergotamines, antiseizure drugs, muscle relaxants, etc. Other than drugs, certain lifestyle changes like lifestyle changes, regular exercise, avoiding certain foods, participating in different biofeedback and relaxation techniques etc.