Headache is pain in any region of the head. Headaches may occur on one or both sides of the head, be isolated to a certain location, radiate across the head from one point, or have a viselike quality.

A headache may appear as a sharp pain, a throbbing sensation or a dull ache. Headaches can develop gradually or suddenly, and may last from less than an hour to several days.

Causes

Primary Headaches

A primary headache is caused by over-activity of or problems with pain-sensitive structures in your head. A primary headache isn't a symptom of an underlying disease. Chemical activity in your brain, the nerves or blood vessels surrounding your skull, or the muscles of your head and neck (or some combination of these factors) can play a role in primary headaches. Some people may also carry genes that make them more likely to develop such headaches.

The most common primary headaches are:

• Cluster headache
• Migraine (with and without aura)
• Tension headache (also known as tension-type headache)
• Trigeminal autonomic cephalalgia (TAC), such as cluster headache and paroxysmal hemicrania

A few headache patterns also are generally considered types of primary headache, but are less common. These headaches have distinct features, such as an unusual duration or pain associated with a certain activity.

Although generally considered primary, each could be a symptom of an underlying disease. They include:

• Chronic daily headaches (for example, chronic migraine, chronic tension-type headache, or hemicranias continua)
• Cough headaches
• Exercise headaches
• Sex headaches

Some primary headaches can be triggered by lifestyle factors, including:

• Alcohol, particularly red wine
• Certain foods, such as processed meats that contain nitrates
• Changes in sleep or lack of sleep
• Poor posture
• Skipped meals
• Stress

Secondary headaches

A secondary headache is a symptom of a disease that can activate the pain-sensitive nerves of the head. Any number of conditions — varying greatly in severity — may cause secondary headaches.

Possible causes of secondary headaches include:

• Acute sinusitis
• Arterial tears (carotid or vertebral dissections)
• Blood clot (venous thrombosis) within the brain — separate from stroke
• Brain aneurysm (a bulge in an artery in your brain)
• Brain AVM (brain arteriovenous malformation) — an abnormal formation of brain blood vessels
• Brain tumor
• Carbon monoxide poisoning
• Chiari malformation (structural problem at the base of your skull)
• Concussion
• Dehydration
• Dental problems
• Ear infection (middle ear)
• Encephalitis (brain inflammation)
• Giant cell arteritis (inflammation of the lining of the arteries)
• Glaucoma (acute angle closure glaucoma)
• Hangovers
• High blood pressure (hypertension)
• Influenza (flu) and other febrile (fever) illnesses
• Intracranial hematoma (blood vessel ruptures with bleeding in or around the brain)
• Medications to treat other disorders
• Meningitis (inflammation of the membranes and fluid surrounding your brain and spinal cord)
• Monosodium glutamate (MSG)
• Overuse of pain medication
• Panic attacks and panic disorder
• Post-concussion syndrome
• Pressure from tight headgear, such as a helmet or goggles
• Pseudotumor cerebri (increased pressure inside the skull), also known as idiopathic intracranial hypertension
• Stroke
• Toxoplasmosis
• Trigeminal neuralgia (as well as other neuralgias, all involving irritation of certain nerves connecting the face and brain)

Some types of secondary headaches include:

• External compression headaches (a result of pressure-causing headgear)
• Ice cream headaches (commonly called brain freeze)
• Rebound headaches (caused by overuse of pain medication)
• Sinus headaches (caused by inflammation and congestion in sinus cavities)
• Spinal headaches (caused by low pressure or volume of cerebrospinal fluid, possibly the result of spontaneous cerebrospinal fluid leak, spinal tap or spinal anesthesia)
• Thunderclap headaches (a group of disorders that involves sudden, severe headaches with multiple causes)

Treatment

Headaches are treated with a variety of modalities, including medication, hot/cold packs, manual manipulation, and interventions. Interventional procedures include Trigger Point Injections, Epidural Steroid Injections, Cervical Medial Branch Blocks, & Botox.

REFERENCES:

http://www.mayoclinic.org/symptoms/headache/basics/definition/sym-20050800