why do you have to change fork oil?

[derek the 2 stroke]

my manual says to change my fork oil really often,cant remember exactly how often but i think it was every race.Why?what happens if you dont change it?

 

[whenfoxforks-ruled]

When my son gets done with a moto,you can not touch the suspension,it gets that hot! New the oil is questionable. Trail riding,I do not know,check the temp! The oil gets trashed with aluminum flashing.