* Reduced cellular defense mechanisms
** Children younger than 4 months exposed to various environmental agents
** Pregnant women are considered vulnerable to exposure of high levels of nitrates in drinking water
** Cytochrome b5 reductase deficiency
** G6PD deficiency
** Hemoglobin M disease
** Pyruvate kinase deficiency
* Various pharmaceutical compounds
** Local anesthetic agents, especially prilocaine and benzocaine.
** Amyl nitrite, chloroquine, dapsone, nitrates, nitrites, nitroglycerin, nitroprusside, phenacetin, phenazopyridine, primaquine, quinones and sulfonamides
* Environmental agents
** Aromatic amines (e.g. p-nitroaniline, [http://www.gtfch.org/cms/images/stories/media/tk/tk73_2/Bakdash.pdf patient case])
** Arsine
** Chlorobenzene
** Chromates
** Nitrates/nitrites
** Umbellulone
* Inherited disorders
** Some family members of the Fugate family in Kentucky, due to a recessive gene, had blue skin from an excess of methemoglobin.
* In cats
**Ingestion of paracetamol (i.e. acetaminophen, tylenol)