Headache on the Left Side of Head: 7 Causes (& What to Do)

Updated in July 2023

Headaches on the left side of the head are commonly caused by direct blows to the head and other mild injuries, however they can also be caused by ear infections, tooth infections or migraines. This type of headache may be accompanied by other symptoms like local swelling, nausea or fever. 

Although headaches on the left side of the head are not always a concerning finding, left-sided headaches that appear with symptoms like weakness on one side of the body, vision loss or seizures may be a sign of a more serious condition, like a brain tumor or serious brain injury. In these cases, imaging tests, like a CT or MRI, may be ordered. 

If your headaches on the left side occur frequently, you should consult your doctor for further assessment to rule out any serious conditions and to start treatment as necessary. 

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What causes left-sided headaches?

Headaches on the left side of the head can occur due to:

1. Wounds and injuries

A headache on the left side of the head can occur due to wounds and injuries that occur in the area. Generally, other symptoms do not emerge, other than some pain and mild swelling, which resolves within a few days. 

What to do: This type of headache tends to improve within a few days. However, if the pain is intense or persists for more than a week, you should see a doctor, who may recommend analgesics like acetaminophen. 

If you also experience symptoms like vomiting, seizures or loss of consciousness immediately after the injury, you should proceed to an emergency room for a more thorough assessment to rule out a serious brain injury. 

2. Migraine

A migraine can cause a left side headache. It is usually a throbbing pain that is accompanied by other symptoms like nausea, vomiting, and sensitivity to lights or noises. Learn more about migraine symptoms that can emerge. 

Generally, migraine pain worsens with physical activity, like walking or going up stairs. It can emerge with other symptoms like blurry vision and light flashes, which can occur before or during the headache. 

What to do: If you experience a migraine, you should see a doctor or neurologist for evaluation and treatment as necessary. Treatment may involve medications, like analgesics and anticonvulsants, and lifestyle changes, like sleeping, ensuring adequate sleep routines and regular exercise. Read more about what can cause migraines and how they are treated. 

3. CNS vasculitis

Headaches on the left side of the head can be caused by vasculitis, or specifically CNS vasculitis, which is characterized by swelling of arteries and veins in the brain and spine. Generally speaking, these blood vessels are protected by the blood-brain barrier, however swelling can occur if the immune system is activated to protect these vessels from a foreign antigen. 

The antigen causing swelling is not easily identifiable or well-understood. It is hypothesized the CNS vasculitis may be triggered by an allergic drug reaction or by severe cocaine abuse. Symptoms of this type of vasculitis include suddenly new headaches, vision loss, memory problems, loss of balance and seizures. 

What to do: These symptoms should be assessed urgently in a hospital setting. Doctors will likley order an MRI, CT scan and/or angiogram to visualize the blood vessels and guide treatment and prevent further complications like brain ischemia and stroke. Treatment involves the administration of high-dose corticosteroids to reduce swelling. 

4. Ear infection 

An ear infection on the left side may cause a headache in this area. Other possible symptoms include fever and ear discharge

What to do: You are advised to consult a family doctor or ENT specialist if you suspect you have an ear infection. Treatment usually involves the use of medications like antibiotics and analgesics. Check-out other ways you can relieve ear pain at home. 

5. Tooth infection

When tooth infections occur on the left side of the mouth, pain can radiate to the areas around the affected teeth and to the head. 

Pain usually worsens when touching the affected tooth or with drinking hot or cold drink. Other common symptoms include swollen gums, easy bleeding and, in more severe cases, fever. 

What to do: If you think you may have a tooth infection, you should see your dentist for assessment and treatment as necessary. Depending on the severity, treatment may involve the use of antibiotics or even the extraction of the affected tooth. In the meantime, learn about how you can relief tooth pain at home

6. Temporal arteritis

Temporal arteritis is an inflammation of the blood vessels. When vessels on the left side of the head are affected, it can cause symptoms like a left side headache, transient vision loss and difficulty chewing. 

This pain tends to worsen with palpation, which can make common tasks like brushing you hair or sleeping on that side more difficulty. Other symptoms may include fever and general malaise. 

What to do: If you suspect you may have temporal arteritis, you should see a rheumatologist for assessment. If confirmed, treatment with medications (like oral corticosteroids) can be used to manage headache and prevent worsening. 

7. Tumors

Although they are rare, brain tumors can also cause left side headaches in some cases. Other symptoms will usually emerge, like seizures, weakness in certain areas of the body, nausea, vomiting  and episodes of temporary vision loss. Check out the brain tumor symptoms that can occur on the left side of the brain. 

The pain tends to be worse in the morning, and when lying down, coughing or with exerting force. Learn more about general cancer symptoms that you shouldn’t ignore.

What to do: If you suspect a brain tumor, you should see your doctor for thorough imaging tests, like CT and MRI. If confirmed, the headache will generally improve when the tumor is treated. Treatment may include surgery and chemotherapy. 

When to see the doctor 

You should consult a doctor if you experience any of the following: 

  • Frequent headaches with no past history or obvious cause
  • Weakness in a certain area of the body
  • Seizures
  • Fainting
  • Vision loss, even if temporary 
  • Double vision
  • Cancer history 
  • Headaches that worsen over time 
  • Worsening of headache with lying down or coughing 
  • Waking up at night from headaches 

In these cases, tests like MRIs or CTs may be ordered to rule out serious conditions, like brain tumors. Results will typically guide treatment, which will be determined by the doctor.