▁head aches ▁caused ▁by ▁d ial ysis , ▁high ▁blood ▁pressure , ▁hypoth y roid ism , ▁and ▁ce phal alg ia ▁and ▁even ▁fast ing ▁are ▁considered ▁secondary ▁head aches . ▁Second ary ▁head aches , ▁according ▁to ▁the ▁same ▁classification ▁system , ▁can ▁also ▁be ▁due ▁to ▁the ▁injury ▁of ▁any ▁of ▁the ▁fa cial ▁structures ▁including ▁teeth , ▁j aws , ▁or ▁tempor om and ib ular ▁joint . ▁Head aches ▁caused ▁by ▁psych iat ric ▁dis orders ▁such ▁as ▁som at ization ▁or ▁psych otic ▁dis orders ▁are ▁also ▁class ified ▁as ▁secondary ▁head aches . ▁ ▁The ▁I CH D - 2 ▁classification ▁puts ▁c ran ial ▁neural gi as ▁and ▁other ▁types ▁of ▁neural gia ▁in ▁a ▁different ▁category . ▁According ▁to ▁this ▁system , ▁there ▁are ▁ 1 9 ▁types ▁of ▁neural gi as ▁and ▁head aches ▁due ▁to ▁different ▁central ▁causes ▁of ▁fa cial ▁pain . ▁Moreover , ▁the ▁I CH D - 2 ▁includes ▁a ▁category ▁that ▁contains ▁all ▁the ▁head aches ▁that ▁cannot ▁be ▁class ified . ▁ ▁Although ▁the ▁I CH D - 2 ▁is ▁the ▁most ▁complete ▁head ache ▁classification ▁there ▁is ▁and ▁it ▁includes ▁frequency ▁in ▁the ▁di agnostic ▁criteria ▁of ▁some ▁types ▁of ▁head aches ▁( prim arily ▁primary ▁head aches ), ▁it ▁does ▁not ▁specifically ▁code ▁frequency ▁or ▁sever ity ▁which ▁are ▁left ▁at ▁the ▁dis cret ion ▁of ▁the ▁exam iner . ▁ ▁N I H ▁▁ ▁The ▁N I H ▁classification ▁consists ▁of ▁brief ▁definitions ▁of