Headaches are any form of discomfort that can be found in the head and can be caused by a wide variety of things which serves as a warning sign that there is a disorder somewhere in the body or in the nervous system. Headaches affect everybody off all ages and can be felt on various levels, ranging from minor to very painful.  
The most common type of headache is due to tension in the body caused from tightness in the muscle in your neck, shoulders, jaw or scalp. Tension can result from symptoms like depression, stress, anxiety, overworking, lack of sleep, strain in the eye, using illegal drugs, eating on and off. Persons who work over lengthy periods of time increase their chances of feeling stressed and can have problems when attempting to sleep. Limited amounts of sleep then can often lead to depression. Both of these situations can cause severe headaches. Not working out can be attributed to stress, depression and headaches. Physical activity has the ability to relax the muscles and endorse proper circulation throughout the body which lessens the chance of a headache.
A person who doesn't take time out to eat on time risk suffering from headaches often. When we don't eat on time, sometime gases form in the body that often go to the head and cause headaches. Not drinking enough fluids also causes dehydration, the body requires fluid in order to work optimally. using illegal drugs can take a toll on the nervous system and disrupt the circulatory system and cause severe headaches.There are certain foods can also cause headaches, especially if you are very sensitive to them. These include dairy foods like chocolate, cheese, foods high in refined sugars like carbonated beverages, preservatives like nitrates and sulfites and flavor enhancers such as artificial sweeteners, Monosodium glutamate. All these elements have in amines which cause the blood vessels to tighten.  
Elements found in your surroundings can trigger off headaches such as the fumes which exhaust from a vehicle. If you work in a factory that emits certain substances this can have serious impact on your health and can. There are goods that are used in your house that contain substances can also cause complications and trigger headaches like bleach (that has chlorine), certain soaps, disinfectants (that have chemical cleaning agents) etc.
There are persons who also suffer from chronic headaches which in most cases is more severe than a headache caused from tension. There are three types of chronic headaches; chronic tension-type headaches, chronic migraine, hemicranias continua and new daily persistent headache.  Migraine headaches may also be due to similar symptoms like depression, high blood pressure, eye problems, and allergies and can cause nausea. There is also what is considered as cluster headaches caused from head trauma, brain tumors and seizures, strokes and inflamed arteries and other sicknesses. Shock experienced in the head from an accident can lead to a lot of long term problems to the head. The affected person over the course of time may endure a lot of painful headaches over time. This may get worse or diminish over time.