Persistent headache on the left side: what should you know?

Migraine commonly affects one side and may bring throbbing pain, nausea, light sensitivity, or an aura. Tension in the neck, scalp, or jaw can also be felt more strongly on one side. Cluster headache causes severe one-sided pain around an eye with tearing or a blocked nose and needs medical review. The left-sided location does not show whether a headache is cancer-related. Brain tumours can present with headache, but diagnosis depends on the whole history, examination, and sometimes imaging. See [Brain Tumour](/conditions/brain-tumour/) and [Glioblastoma](/conditions/glioblastoma/) for general information.

Track the start and end of each episode, pain quality, sleep, meals, fluids, screen exposure, neck position, menstrual timing when relevant, and medicines. Include nausea, aura, tearing, nasal symptoms, weakness, numbness, or speech changes. Rest in a quiet room, drink fluids, and follow only treatment advice that is appropriate for you. Arrange a review if the pattern is new, lasting, escalating, or interfering with normal activity; take your symptom record with you.

Seek emergency care for a sudden severe headache, new weakness or numbness, facial drooping, speech difficulty, confusion, seizure, fainting, vision loss, repeated vomiting, fever with a stiff neck, or pain after head injury. If you have cancer, notify your oncology team about a new persistent headache or neurological symptom. Cancer can sometimes spread to the brain, known as [Brain Metastases](/conditions/brain-metastases/), so new changes should not be ignored.

Ask: Does the pattern resemble migraine, cluster headache, or muscle-related pain? Do I need an eye, neurological, or neck examination? Could any medicine be contributing? What changes mean I should seek emergency care?