As the most common neurological problem seen by GPs worldwide, more than half the world’s population experiences some form of headache each year.

The condition is among the most disabling the world over — leaving sufferers of severe headaches unable to go about their lives for days or weeks at a time.

A headache produces pain felt around the head, but how severe the pain is depends on what type of headache you have.

There’s more than 100, but some are far more common than others — especially tension-type headaches and migraines.

Tension-type headaches

Tension-type headaches are the most common form of headache — up to 30 per cent of the population will experience one each year.

A tension-type headache feels like a dull band of pain, usually sensed across both sides of the head. They can last anywhere from an hour to days on end.

This type of headache got its name because doctors once thought it was caused by muscle tension. It’s now known that tension doesn’t directly contribute to a tension-type headache, but many other factors can. Chief among these are:

• Poor sleep
• Stress
• Bright lights
• Poor posture
• Fatigue

Despite there being clear triggers for a tension-type headache, Deakin University pain expert Dr Michael Vagg said the exact mechanism behind it remains unknown.

“We know that it probably relates to a lowered threshold [for provoking a pain response] in an area called the trigeminal nucleus, which is the sensory processing area which covers the whole head and neck,” he said.

“If you have several things feeding pain input into the trigeminal nucleus at the same time, then that can create this perception of a headache — pain where there isn’t necessarily an injury.”

Migraines

Migraine is the seventh-most disabling condition worldwide according to the Global Burden of Disease 2015 study. About one in 10 people will experience a migraine at some point in their lives, and for many of those, the pain will be recurring throughout their life.

Migraines are typically a more severe pain than a tension-type headache and usually affect one side of the head.

Sufferers may experience disturbances in their vision (like flashing lights or trouble focusing) in the hours before a migraine hits, while nausea and sensitivity to light are common symptoms.

While research into migraines is ongoing, doctors believe they occur because a person’s regulation of blood flow to different parts of the brain is dysfunctional.

As with tension-type headaches, there isn’t a single definitive cause of a migraine, but some potential triggers include fluctuations in hormones, certain food and drink (like wine and cheese), and stress.

There’s also a genetic component to migraines.

“Migraines tend to run in families and they tend to begin in childhood and be a lifelong predisposition,” Dr Vagg said.

“They don’t always continue throughout your life but you always have a tendency towards them if you encounter the right triggers.”

Headaches from medication overuse

Those who suffer chronic daily headaches or migraines will often use painkiller medication as a treatment, but this can cause problems in itself.

Used frequently, pain relief medication sensitises the nervous system, lowering the threshold for future headaches to occur. That’s especially the case with pain medication containing codeine, which has addictive properties.

“If you were using codeine more than a couple of times a week to treat headaches, you’re probably predisposing yourself to have headaches on the days when you try not to have the codeine,” Dr Vagg said.

“In the group of people who have chronic daily headache, which is a headache for some part of the day, pretty much every day, the incidence of medication overuse headaches is actually very high.”

NPS MedicineWise suggests withdrawing completely from a pain relief medication to treat medication overuse headaches, although this usually worsens the symptoms for a period. If you think you may have a medication overuse headache, it’s best to see a specialist.

When you should see a doctor about your headache

Dr Vagg said you should seek out a doctor if you’re concerned about your headache, or if you experience any of the following:

• Visual symptoms such as flashing lights or temporary loss of vision
• Headaches associated with severe nausea
• Headaches associated with difficulty moving the neck
• The sudden onset of a severe headache

This post originally appeared on ABC News.