Tension headaches can be classified into two groups based on frequency:

• Episodic. This type of tension headache occurs on fewer than 15 days a month. They usually last anywhere from 30 minutes up to seven days. The presenting symptom is bilateral  (affecting both sides) tightness around the head, which is not increased with physical activity and not associated with nausea or vomiting.  
  
  
• Chronic. Tension headaches occurring on 15 days a month or more for at least six months may be described as chronic. Twice as many women as men have this form of headache. For many people with this type of headache, the pain is daily or continuous. A tension headache occurring at least six days a week is known as a chronic daily headache. Chronic headaches may persist for many years. When compared to people who do not experience headaches, people with this type of headache are more likely to experience anxiety and depression.

Chronic tension headaches are less common then episodic tension headaches. The severity and duration of chronic and episodic headaches are similar. In addition, either type may be accompanied by scalp tenderness.

A tension headache may also be described as a coexisting migraine and tension-type headache. This term is used to describe the combination of a daily, chronic tension headache and a recurrent migraine. This type of headache is also known as transformed migraine or chronic migraine. In most cases, patients with this condition have a personal history of migraine headaches that can be traced back to adolescence or early adulthood.