There are various causes of a headache on the left side. Understanding the possible causes and their treatments may help a person manage the pain and know when to seek professional care.
Around 50% of adults worldwide have a headache disorder. Some headaches are minor and resolve with home treatment, but some are more severe and need medical care.
If a headache occurs with blurred vision, nausea, or any other symptom that causes concern, seek medical attention. If a person has a sudden, severe headache and weakness on one side of the body or confusion, they need emergency care.
Several kinds of headaches can cause pain on the left side, including migraines and cluster headaches. We describe these in detail below.
Generally, doctors classify headaches as “primary” or “secondary.” For a person with a primary headache, pain is the main symptom. A secondary headache results from another health issue, such as:
- a brain tumor
- a stroke
- an infection
The headaches that result can occur in any location, including the left side.
Migraine can cause a moderate to severe headache on the left side. The condition affects 12% of people in the United States, including 17% of women and 6% of men.
A migraine headache may throb and be worse on one side. The pain may begin around the eye or temple, then spread across the head.
Some other symptoms of migraine include:
- changes to vision
- nausea and vomiting
- extreme sensitivity to sound, light, touch, or smell
- numbness or a tingling sensation in the face or extremities
One rare type of migraine, called a hemiplegic migraine, can also cause weakness in the limbs and face on one side of the body.
A migraine episode typically lasts 4–72 hours. A person may need to lie down in a darkened room and rest until the symptoms pass.
Experts do not understand the exact causes, but genetic factors and environmental triggers appear to play a role.
Common triggers include:
- stress, a factor in 80% of cases
- hormonal changes, present in 65% of cases
- certain foods, such as alcohol, cheese, and chocolate
- sleeping too much or too little
- bright lights or lights that flicker
- odors, such as perfumes
A cluster headache can cause severe pain on one side of the head, often around the eye. The pain can be very severe, and it may feel sharp, burning, or piercing.
About 1% of people in the United States experience cluster headaches. When they occur, the headaches tend to arise in several episodes for 4–12 weeks, then stop, possibly for several years. They often affect the same side each time.
Common features include:
- pain behind one eye, one temple, or one side of the forehead
- pain that starts at night, usually 1–2 hours after going to sleep
- pain that peaks after 5–10 minutes
- severe pain that lasts 30–60 minutes
- less intense pain that may continue for up to 3 hours
Related symptoms may include:
- a blocked or runny nose
- a drooping eyelid
- watering and redness in one eye
- a flushed or sweaty face
The exact cause is unknown, but experts believe that it involves a part of the brain called the hypothalamus and the nerves and blood vessels of the trigeminal system, which affects the eyes and face.
Cluster headaches often happen at the same time each day. They may also be more common in the spring or fall, and people may confuse them with allergy headaches. They usually affect people aged 20–50 years and 80% of them are males.
This type of headache can result from an injury to the neck, such as whiplash, or arthritis, or other changes in the vertebrae at the top of the spine.
It can cause:
- moderate to severe pain that starts in the neck and spreads to the eyes and face on one side
- a stiff neck and reduced range of motion
- pain around the eyes, neck, shoulders, and arms
- blurred vision
- sensitivity to light and sound
Steroid injections and nonsteroidal anti-inflammatory drugs, such as ibuprofen (Advil), may help manage the pain. With treatment, cervicogenic headaches should resolve within 3 months, though they may recur.
The pain and other symptoms may be cyclical and flare up periodically, though the frequency varies from person to person.
An autoimmune attack in which the body responds as if its blood vessels were harmful substances can lead to vasculitis, a type of blood vessel inflammation.
A common type of vasculitis is giant cell arteritis, also called temporal arteritis. This affects blood vessels in the head. It usually occurs in people aged over 50 years.
Vasculitis can cause a headache that is similar to a “thunderclap headache.” The pain is severe, and there is often no clear cause. With a thunderclap headache, the pain is most intense within 1 minute and lasts for at least 5 minutes. With a similar headache caused by vasculitis, the pain may take a little longer to develop.
Other symptoms can include:
- a sudden loss of vision
- pain on one side of the head or behind the eye
- pain when chewing
Anyone who experiences these symptoms should receive medical advice. Not treating vasculitis can result in permanent vision loss.
A brain aneurysm is a weak spot in a blood vessel in the brain. It does not usually cause symptoms unless it ruptures. In this case, a potentially life-threatening hemorrhage can result.
A person may develop a thunderclap headache, which involves sudden, severe pain. They may feel as if they have been hit hard on the head, and they may also have weakness on one side of the body.
Other possible symptoms include:
- vision changes
- pain or stiffness in the neck
- nausea and vomiting
- sensitivity to light
- loss of consciousness
When to see a doctor
If a person has a headache that is severe or persistent or if the pain occurs with any other symptoms, they should receive medical advice.
Additional symptoms include:
- blurred vision
- nausea and vomiting
- weakness on one side of the body
It is also important to consult a doctor if:
- Headaches first develop after the age of 50.
- There is a significant change in the pattern of headaches.
- Headaches steadily get worse.
- There are changes to the person’s mental function or personality.
- Headaches occur after a blow to the head.
- Headaches make daily life hard to manage.
Anyone with a severe, sudden headache should receive emergency care, as this may be a sign of a stroke or aneurysm.
Treatment and prevention
Many people can treat a headache with over-the-counter medication and rest.
When possible, the following measures may help prevent some types of headaches:
- avoiding or managing stress
- having a regular sleep pattern
- avoiding known triggers
A doctor may prescribe stronger pain relief medications for severe pain.
A headache on the left side may result from migraines, vasculitis, cluster headaches, or other types.
Often, a person can treat a headache at home with over-the-counter remedies and rest. However, if headaches are severe, persistent, or otherwise concerning, contact a healthcare professional.
Anyone with a sudden, severe headache and weakness on one side of the body or confusion requires emergency care.