There are many classifications of headache, but all fit into three basic categories.

The vast majority of headaches that patients suffer can be easily fit into the first category, or primary headache.
Primary headaches afflict millions every day, and are not a serious or life threatening issue. Primary headaches can occasionally become very painful, or can become a chronic problem. Although this isn't life threatening, it can be a serious impediment to quality of life.

Fixing these kinds of primary headaches can be very important to the daily life and functioning of a patient. Correcting issues regarding primary headaches can usually be done with the use of over the counter medications.

Cluster headaches present with a far greater pain level.
Although not life threatening in itself, the associated is very serious and often debilitating. Cluster headaches are known as such because of the groupings they occur in, and can be very hard to predict. This means that treatment over the course of a lifetime is difficult, resulting in first occurences that are hard to avoid.

A cluster headache can disable an individual, so great is the pain. Pain usually centers behind one or both eyes, and presents with visible symptoms like runny and watery eyes and nose. Patients can become overwhelmed with the pain associated with cluster headaches.

Treatment of this pain is very important and should be done as soon as possible. Over the counter medications are typically inadequate in these situations.

Secondary headaches are the third and rarest form of headache types.
As the name implies, a secondary headache results from another issue. Secondary headaches result from a problem in the brain that may or may not be life threatening.

In the most serious of cases, a secondary headache can be a sign of a brain tumor. There are dozens of other possible secondary headache causes. Regular headaches should be a sign to see the doctor.

The vast majority of headaches suffered fit into the primary headache category. As many as 90% of primary headaches result from the "tension" variety of headache. A tension headache takes place when cranial muscles contract, putting a painful amount of pressure on the head.

The pain can typically be felt around the temples and around the eyes. Relief can usually be found with a variety of over the counter medications.

Evan