Tension Headache: This is the most common type of headache in adults, often described as a band or a squeezing sensation around the forehead, usually bilateral but can be unilateral. It's more common in women and can start at any age, including after 40.

Migraine: Although migraines often start at a younger age, they can begin at any time, including after 40. They are typically unilateral, throbbing, and can be accompanied by nausea, vomiting, and sensitivity to light and sound.
Cluster Headache: These are severe, unilateral headaches that occur in clusters or cycles. They are less common than migraines or tension headaches but can start at any age, including after 40.
Hypnic Headache: Also known as "alarm clock headache," these are rare but can occur, typically in older adults, and are characterized by recurrent headaches that wake the patient from sleep.

Subarachnoid Hemorrhage: Although rare, this condition is life-threatening and requires immediate medical attention. It's usually characterized by a sudden, severe headache (often described as "the worst headache of my life"), which can be unilateral or bilateral.
Temporal Arteritis (Giant Cell Arteritis): This condition is more common in individuals over 50 but can occur in those over 40. It presents with unilateral headache, scalp tenderness, jaw claudication, and visual disturbances. Prompt diagnosis and treatment are crucial to prevent blindness.
Stroke or Transient Ischemic Attack (TIA): Headache can be a symptom of stroke or TIA, especially if accompanied by other neurological deficits such as weakness, numbness, or difficulty with speech.

Trigeminal Neuralgia: Characterized by sudden, severe, shock-like or stabbing pain around the eyes, lips, or nose, typically on one side of the face. It's more common in older adults.
Idiopathic Intracranial Hypertension (IIH): Also known as pseudotumor cerebri, this condition can cause headache, usually worse in the morning and exacerbated by maneuvers that increase intrathoracic pressure. It's often associated with obesity and can lead to visual disturbances.
Cervicogenic Headache: Originates from the cervical spine and is typically unilateral, corresponding to the distribution of the cervical nerve root involved. It can be accompanied by neck pain and limited range of motion.