Headache attributable to disorders of homeostasis represents a diverse diagnostic category in which external (i.e., high-altitude) or internal (i.e., fasting) demands exceed homeostatic capacity, resulting in symptomatic headaches. Metabolic headaches, especially fasting headache, have been observed to be common in the general population. In many cases, a history of migraine is a risk factor, consistent with the hypothesis of an adaptive, evolutionary role of headache to warn against environmental and physiological threats. Because many exposures may also be interpreted as migraine triggers, some authors have considered certain disorders in this category to more accurately represent primary headache disorders. Nonetheless, these disorders not only represent important clinical entities, recognition of which may prevent medical morbidity, but also interesting exposure-response models to further our understanding regarding headache pathophysiology.