Headaches occur when nerves in your head transmit pain messages to your brain. The reasons why this might happen are often clear, for example, hitting your head. Headaches are also a symptom of numerous common conditions, from sinusitis and colds to allergies and fevers, as well as chronic disorders like fibromyalgia.

Other common reasons for developing a headache include stress, which makes the muscles in your head and neck too tense, insufficient or poor-quality sleep, and dehydration. Conditions that affect the main nerves in your head and face, like occipital neuralgia and trigeminal neuralgia, can also cause severe pain. However, many types of headaches develop for no identifiable reason.