Hexamine could decompose to formaldehyde, which is a listed potential carcinogen.
Hexamine is a white crystalline compound that is highly soluble in water. Crystals of hexamine burn with a yellow flame and the material has been used in small indoor fireworks employing magnesium and lithium salts. In contrast to metaldehyde formerly used for this purpose it does not produce poisonous formaldehyde when lighted indoors. Lancaster states that “hexamine would be quite useful as a fuel, but does not appear to have found much application, possibly because of the cost.” Some armys employ ESBIT fuel to allow the soldiers to cook their meals while in field. Hexamine is the main ingredient.