Pain on the left side of the head is generally caused by a type of headache, according to Mayo Clinic and WebMD. People who experience the pain formore than 15 days a month for several months in a row are considered to have chronic headaches, which are usually not caused by any other condition.
Migraines are a common cause for pain on the left side of the head. They can create moderate to severe pain that can often be felt on one side of the head, as stated by WebMD. The pain sometimes takes over the entire head, but in most cases it sticks to one side or shifts from side to side. Other symptoms include sensitivity to light, fatigue, dizziness, blurred vision, nausea, loss of appetite and eye problems, such as flashing dots, jagged lines or blind spots.
A hemicrania continua headache is commonly felt on only one side of the head. This type of headache is often combined with a tearing or redness in the eye on the affected side of the head, a runny or congested nose, a feeling of restlessness and a drooping eyelid or a narrowing pupil.
Other types of headaches that can affect only the left side of the head include tension headaches, sinus headaches and cluster headaches. The Mayo Clinic website recommends individuals see a doctor if they have more two or more headaches in a week, if pain medication does not help the headaches, if patterns change or worsen in the headaches or if the headaches are debilitating.