Victims prayed for relief from Asclepius, the god of medicine.

And if pain continued,

a medical practitioner would perform the best-known remedy—

drilling a small hole in the skull to drain supposedly infected blood.

This dire technique, called trepanation,

often replaced the headache with a more permanent condition.

Fortunately, doctors today don't resort to power tools to cure headaches.

But we still have a lot to learn about this ancient ailment.

Today, we've classified headaches into two camps—

primary headaches

and secondary headaches.

The former are not symptomatic of an underlying disease, injury, or condition;

they are the condition.

But we'll come back to them in a minute

because while primary headaches account for 50% of reported cases,

we actually know much more about secondary headaches.

These are caused by other health problems,

with triggers ranging from dehydration and caffeine withdrawal

to head and neck injury,

and heart disease.

Doctors have classified over 150 diagnosable types,

all with different potential causes, symptoms, and treatments.

But we'll take just one common case —a sinus infection—as an example.

The sinuses are a system of cavities

that spread behind our foreheads, noses, and upper cheeks.

When our sinuses are infected,

our immune response heats up the area,

roasting the bacteria and inflaming the cavities well past their usual size.

The engorged sinuses put pressure on the cranial arteries and veins,

as well as muscles in the neck and head.

Their pain receptors, called nociceptors, trigger in response,

cueing the brain to release a flood of neuropeptides

that inflame the cranial blood vessels, swelling and heating up the head.

This discomfort, paired with hyper-sensitive head muscles,

creates the sore, throbbing pain of a headache.

Not all headache pain comes from swelling.

Tense muscles and inflamed, sensitive nerves

cause varying degrees of discomfort in each headache.

But all cases are reactions to some cranial irritant.

While the cause is clear in secondary headaches,

the origins of primary headaches remain unknown.

Scientists are still investigating potential triggers for the three types of primary headaches:

recurring, long-lasting migraines;

intensely painful, rapid-fire cluster headaches;

and, most common of all, the tension headache.

As the name suggests,

tension headaches are known for creating the sensation of a tight band squeezed around the head.

These headaches increase the tenderness of the pericranial muscles,

which then painfully pulse with blood and oxygen.

Patients report stress, dehydration, and hormone changes as triggers,

but these don't fit the symptoms quite right.

For example, in dehydration headaches,

the frontal lobe actually shrinks away from the skull,

creating forehead swelling

that doesn't match the location of the pain in tension headaches.

Scientists have theories for what the actual cause is,

ranging from spasming blood vessels

to overly sensitive nociceptors,

but no one knows for sure.

Meanwhile, most headache research is focused on more severe primary headaches.

Migraines are recurring headaches, which create a vise-like sensation on the skull

that can last from four hours to three days.

In 20% of cases, these attacks are intense enough to overload the brain with electrical energy,

which hyper-excites sensory nerve endings.

This produces hallucinations called auras,

which can include seeing flashing lights

and geometric patterns and experiencing tingling sensations.

Cluster headaches, another primary headache type,

cause burning, stabbing bursts of pain behind one eye,

leading to a red eye, constricted pupil, and drooping eyelid.

What can be done about these conditions, which dramatically affect many people's quality of life?

Tension headaches and most secondary cases

can be treated with over-the-counter pain medications,

such as anti-inflammatory drugs that reduce cranial swelling.

And many secondary headache triggers,

like dehydration,

eye strain,

and stress,

can be proactively avoided.

Migraines and cluster headaches are more complicated,

and we haven't yet discovered reliable treatments that work for everyone.

But thankfully, pharmacologists and neurologists are hard at work

cracking these pressing mysteries that weigh so heavily on our minds.