Pain from a headache usually subsides within a few hours and isn’t cause for worry. But intense pain on either side of the head or pain that doesn’t go away could be a sign of something more serious.

There are a variety of reasons that you might have pain or pressure only on the left side of your head. Keep reading to learn about the possible causes and when to call your doctor.

There are many different kinds of headaches, from migraine to tension. Knowing which one you have can help you get the right treatment. Here are a few of the most common:

Tension

Tension headaches are the most common type of headache worldwide. They affect about 75 percent of adults.

Feels like: A band tightening around your head, squeezing your face and scalp. You can feel the pressure along both sides and the back of your head. Your shoulders and neck might also be sore.

Migraine

Migraine is one of the most common illnesses in the world and affects about 1 in 6 people in the United States. Women are two to three times more likely to experience migraine attacks than men.

Feels like: An intense, throbbing pain, often one side of the head. The pain is often accompanied by symptoms like nausea, vomiting, and sound and light sensitivity. Migraine can also come with or without aura. Aura is the change in vision, speech, and other sensations that occur before the migraine attack starts.

Cluster

Cluster headaches are rare but intensely painful headaches that are more often reported by men. They get their name from their pattern: The headaches arrive in clusters over a period of days or weeks. These cluster attacks are followed by remissions — headache-free periods that can last for months or years.

Feels like: Intense pain on one side of your head. The eye on the affected side might be red and watery. Other symptoms include a stuffed or runny nose, sweating, and flushing of the face.

Sinus

Sinus headaches are rare but severe headaches that can be easy to confuse with migraine. They’re caused by an infection in the sinuses and accompanying inflammation.

Feels like: Intense pressure and pain in the sinus cavities, usually on both sides of the head but possibly isolated to one. Could also lead to pain in the ear, eye, or jaw. Symptoms will also include a thick nasal discharge.

Chronic

Chronic headaches can be any type — including migraine or tension headaches. They’re called chronic because they happen at least 15 days a month for 6 months or more.

Feels like: A dull throbbing pain, intense pain on one side of the head, or a vice-like squeezing, depending on which type of headaches you get.

Left side headache causes range from lifestyle factors like skipping meals to overusing medications.

Lifestyle factors

If you experience frequent headaches, making changes to your lifestyle may greatly ease your symptoms. Any of these factors can trigger a headache:

  • Alcohol: Beer, wine, and other alcoholic drinks contain ethanol, a chemical that triggers headaches by widening blood vessels.
  • Skipping meals: Your brain needs sugar (glucose) from foods to function optimally. When you don’t eat, your blood sugar level falls. This is called hypoglycemia. A headache is one of the symptoms.
  • Stress: When you’re under stress, your body releases “fight, flight, or freeze” chemicals. These chemicals tense your muscles and change blood flow, both of which cause headaches.
  • Food: Certain foods are known to cause headaches, especially ones that contain preservatives. Common food triggers include aged cheeses, red wine, nuts, and processed meats like cold cuts, hot dogs, and bacon.
  • Lack of sleep: Insomnia can set off headaches. Once you have headaches, the pain can also make it harder to sleep at night. People with sleep disorders like obstructive sleep apnea are more likely to get headaches, in part because their sleep is disrupted.

Infections and allergies

Headaches are often a symptom of respiratory infections like a cold or the flu. Fever and blocked sinus passages can both set off headaches. Allergies trigger headaches via congestion in the sinuses, which causes pain and pressure behind the forehead and cheekbones.

Serious infections like encephalitis and meningitis cause more intense headaches. These illnesses also produce symptoms like seizures, high fever, and a stiff neck.

Medication overuse

Drugs that treat headaches can lead to more headaches if you use them more than 2 or 3 days a week. These headaches are known as medication overuse headaches or rebound headaches. They occur almost every day, and the pain starts when you wake up in the morning.

Medications that can cause overuse headaches include:

Neurological causes

Nerve problems can sometimes be the source of head pain.

  • Occipital neuralgia: The occipital nerves run from the top of your spinal cord, up your neck, to the base of your skull. Irritation of these nerves can cause an intense, severe, stabbing pain in the back of your head or the base of your skull. The pain lasts from a few seconds to several minutes.
  • Giant cell arteritis: Also called temporal arteritis, this condition is caused by inflammation of blood vessels — including the temporal arteries along the side of the head. Symptoms can include headaches and pain in the jaw, shoulders, and hips, along with visual changes.
  • Trigeminal neuralgia: This condition affects the trigeminal nerve, which provides feeling to your face. It causes a severe and sudden jolt of shock-like pain in your face.

Other causes

Pain on the left side of your head may also result from:

  • Tight headgear: Wearing a helmet, glasses, or other protective headgear that’s too tight can put pressure on one or both sides of the head and cause pain.
  • Concussion: A hard hit to the head can cause this type of traumatic brain injury. Concussions produce symptoms like headaches, confusion, nausea, and vomiting.
  • Glaucoma: This rise in pressure inside the eye can lead to blindness. Along with eye pain and blurred vision, its symptoms can include a severe headache.
  • High blood pressure: Normally, high blood pressure doesn’t cause symptoms. But in some people, headaches can be a sign.
  • Stroke: Blood clots can block blood vessels to the brain, cutting off blood flow and causing a stroke. Bleeding inside the brain can also cause a stroke. A sudden, severe headache is one warning sign of a stroke.
  • Brain tumor: A tumor can cause an intense, sudden headache along with other symptoms such as vision loss, speech problems, confusion, trouble walking, and seizures.

Usually, headaches aren’t serious, and you can often treat them yourself. But sometimes, they can signal a more serious problem. Call your doctor or get emergency help if:

  • the pain feels like the worst headache of your life
  • you’ve had a change in the pattern or severity of your headaches
  • the headaches wake you up at night
  • the headaches started after a blow to the head

You should also see your doctor if you’re experiencing any of these symptoms alongside your headache:

  • confusion
  • fever
  • stiff neck
  • vision loss
  • double vision
  • pain that increases when you move or cough
  • numbness, weakness
  • pain and redness in your eye
  • loss of consciousness

Your doctor or specialized neurologist will do a physical exam. You’ll be asked about your medical history and what symptoms you’re having.

Keeping a journal of your headaches and triggers can be extremely helpful for diagnosis. They might ask you questions like these:

  • When did the headaches start?
  • What does the pain feel like?
  • What other symptoms do you have?
  • How often do you get headaches?
  • What seems to trigger them?
  • What makes the headaches better? What makes them worse?
  • Is there a family history of headaches?

Your doctor may be able to diagnose your headache based on symptoms alone. But if they aren’t sure about what’s causing your headaches, they may recommend computed tomography (CT) or magnetic resonance imaging (MRI):

  • A CT scan uses a series of X-rays to create cross-sectional pictures of your brain. It can diagnose bleeding in your brain and certain other abnormalities.
  • An MRI uses powerful magnets and radio waves to create detailed pictures of your brain and its blood vessels. It provides a more detailed brain image than a CT scan. It can help diagnose strokes, bleeding in the brain, tumors, structural problems, and infections.

There are countless headache remedies or hacks that you might have heard about over the years. Here are a few of the most common ones to try:

At-home treatments

  • Apply a warm or cool compress to your head, neck, or both.
  • To ease stress, soak in a warm bath, practice deep breathing, or listen to calming music.
  • Take a nap, and make sure you’re getting plenty of rest at night.
  • Eat something if your blood sugar is low.
  • Take an over-the-counter pain reliever such as aspirin, ibuprofen (Advil), or acetaminophen (Tylenol).
  • Use a massage tool to help relieve tension in your neck and shoulders.
  • Try a pillow designed to relieve neck pain.

Clinical treatments

Your doctor may recommend a variety of treatments depending on the severity and cause of your headaches. Options include:

A few different types of headaches cause pain on only one side of your head. You can usually relieve these headaches with over-the-counter medications and lifestyle changes like relaxation and rest.

See your doctor for headaches that are severe or that interfere with your life. Your doctor can find out what’s causing your headaches and recommend treatments to help manage your pain.