If you have a left-sided headache, you may wonder if it could be due to something serious. Headaches are very common. More than 90 percent are primary headaches, meaning they are not due to an underlying brain disease or injury. Migraine, tension-type and cluster headaches are primary headache disorders that can cause left-sided pain. Although symptoms can be intense and disabling, primary headaches are not life-threatening. Secondary headaches result from problems with the brain, blood vessels, nerves or facial structures. Some of these, like sinus headache, are bothersome but rarely pose a serious health threat. Others, like a brain bleed, can be fatal. The character, severity, location and duration of headache pain, aggravating or relieving factors, and any accompanying symptoms help narrow the list of possible causes of a left-sided headache.
Migraine is a frequent cause of one-sided head pain. An August 2010 article from the Cleveland Clinic Center for Continuing Education reports that migraines occur in 12 to 18 percent of people worldwide. They are thought to be inherited and affect 3 times more women than men. Most migraines cause throbbing, pounding or pulsing pain located at the temple or behind the eye. Migraine pain usually stays on one side of the head but can spread to involve both sides. The pain worsens with physical activity and is typically accompanied by sensitivity to light, sound and sometimes smell. Nausea and vomiting are common.
Migraines generally last 6 to 72 hours. Sufferers typically want to lie quietly in a dark room or sleep, which often resolves the attack. Some people have identifiable triggers, like stress or relief of stress, certain foods or additives, caffeine or alcohol, or hormonal states, like menstruation. In the days prior to the migraine, a prodrome may occur with symptoms like mood and appetite changes, yawning and fatigue. Approximately 15 to 20 percent of people with migraine experience an aura that heralds the headache. Auras are neurologic symptoms, like seeing flashing lights or experiencing a pins-and-needles sensation. The underlying cause of migraine is not completely understood but is thought to involve a combination of changes in brain function and hypersensitivity of nerves surrounding the brain and its blood vessels.
Tension-type headaches can cause one-sided pain, but this happens less often than with migraines. Tension-type headaches are far more common than migraines. According to the International Headache Society, 30 to 78 percent of people are affected over their lifetime. Tension-type headaches are slightly more common in women than men. The discomfort is generally described as tight, pressing or viselike pain going across the forehead or the back of the head. It is sometimes felt behind the eyes and might spread to the entire head.
The pain is typically worse at the end of the day, does not increase with physical activity, and is less strongly associated with nausea and light sensitivity than migraine headaches -- although there can be blurry vision. A person with a tension-type headache might have tight neck and shoulder muscles, as well as tenderness of the scalp or jaw joint. Poor posture, prior neck injury, teeth grinding and stress can predispose a person to tension-type headache. These headaches are thought to be caused by hypersensitivity in muscle and its surrounding tissue -- and, in some cases, to changes in the brain as well.
Cluster headaches comprise a group of conditions called the trigeminal autonomic cephalalgias, which typically cause one-sided head pain. Although such headaches are far less common than migraines and tension-type headaches, roughly 500,000 Americans experience cluster headaches at least once in their lifetime, according to a May 2013 "American Family Physician" article. Seventy percent of cases begin before age 30. The pain of a cluster headache is described as a severe, steady, boring sensation behind one eye that may spread to the face, temple or upper neck. Attacks often awaken a person in the early morning and are accompanied by restless agitation. There is typically also tearing and redness of the eye and nasal congestion on the same side as the pain. There can be redness of the face, swelling or drooping of the eyelid or constriction of the pupil on the same side.
Attacks typically last 15 minutes to 3 hours and can occur up to 8 times per day, often for 6 to 12 weeks before remitting. Some people experience remissions of up to a year before the attacks resume. Others have a chronic form of the disorder. Cluster headaches are often initially misdiagnosed as allergies, sinus disease or migraines. The underlying cause appears to be related to overactivity of the parasympathetic nervous system -- part of the involuntary nervous system that maintains the body's constant internal state.
One-sided headaches can occur due to a head or neck injury. Head trauma can lead to headache shortly after the injury due to bleeding in or around the brain, bone fractures or tearing of the nerves in the brain. Injury-related headaches may also develop in a delayed fashion, as in the post-concussion syndrome. With this condition, migrainelike headaches can be accompanied by fatigue, trouble concentrating, memory problems, insomnia, anxiety, dizziness and personality changes.
Neck injury may be associated with the one-sided cervicogenic headaches -- meaning the headache occurs due to an injury or abnormality in the neck. This type of headache can be provoked by moving the neck certain ways, pressing on tender points on the neck or assuming an awkward head position. Cervicogenic headaches are sometimes accompanied by arm pain on the same side.
Inflammatory Causes of Headache
Giant cell arteritis (GCA), also known as temporal arteritis, is an inflammatory disease of the arteries, especially those of the scalp, head and neck. The arteries at the temples are most commonly involved. Inflammation causes narrowing of the blood vessels, commonly resulting in a one-sided, persistent, throbbing headache at the temple. Other symptoms related to inflammation of head arteries include scalp tenderness, jaw pain when chewing, and blurry or double vision. GCA can also cause generalized symptoms, such as weight loss, sweats, fatigue, low-grade fever, and weakness in the arms and legs. GCA occurs almost exclusively in people older than 50. Most people diagnosed with the disorder are in their 70s. Due to the risk of vision loss, it is vital to be evaluated early for this treatable disorder.
Other causes of inflammation -- such as sinusitis, ear infections, and dental or jaw problems -- could cause left-sided headaches at any age. Systemic bacterial and viral illnesses can also sometimes cause one-sided headaches, especially in those vulnerable due to primary headache disorders. Although rare, a brain abscess or another localized infection of the brain or its protective layers can lead to a one-sided headache.
Blood Vessel Causes of Headache
One-sided headache and neck pain can be caused by carotid or vertebral artery dissection. A dissection is a tear in the inner lining of the artery. Dissection of the carotid artery or vertebral artery, both of which supply blood to the brain, may be caused by trauma to the neck, atherosclerosis or a congenital blood vessel problem called fibromuscular dysplasia. In younger people there is often no known cause. Arterial dissection can lead to stroke, causing symptoms like difficulty speaking, numbness, weakness, dizziness and problems with balance and coordination.
Stroke alone can cause one-sided headache. A stroke occurs when lack of blood flow to part of the brain deprives the area of the oxygen and nutrients needed to survive. Strokes may be caused by a blood clot blocking a vessel or bleeding in the brain. The symptoms of stroke depend on the area of the brain that is affected, and they may include problems with speech, movement, sensation, vision and coordination. A headache accompanied by any of these symptoms is a medical emergency.
Other Causes of One-Sided Headache
Glaucoma, a disorder involving increased pressure in the eye, can cause severe headaches on one side, with pain around the eye or in the forehead. Other symptoms may include seeing halos around lights, decreased vision, redness of the eye and vomiting.
Brain tumors or other space-occupying masses in the brain, such as blood vessel malformations, typically cause a generalized headache. However, in some cases a one-sided headache is an initial symptom. When a one-sided headache is due to a brain mass, there are generally other symptoms, like double vision, trouble with balance, weakness, seizures and other neurological abnormalities detected by a physical examination.
Warnings and Precautions
If you have a new left-sided headache that is getting progressively worse, see your healthcare provider as soon as possible -- especially if you are older than 50 or have cancer or HIV/AIDS. If your headache came on suddenly and is severe, seek emergency medical care. Also seek urgent attention for a headache accompanied by any warning signs and symptoms, including:
-- Eye redness or a drooping eyelid
-- Seeing halos around lights, double vision or other changes in your vision
-- Fever, weight loss or muscle aches
-- Stiff neck
-- Weakness, numbness changes in sensation in your limbs or face
-- Loss of coordination or balance
-- Slurred speech
-- Sleepiness, confusion or irritability
Reviewed by: Tina M. St. John, M.D.