Frey's syndrome is due to:

Both fibres are post-ganglionic.Secretomotor fibres to parotid originate in tympanic branch of CN IX, travel through middle ear, relay in otic ganglion and supply the parotid through auriculotemporal. Similarly, secretomotor fibres to sweat glands of the skin over the parotid area are sympathetic in nature and are post-ganglionic as they relay in cervical sympathetic ganglia.Aberrant re-innervation, i.e. secretomotor fibres of parotid now making connections with secretomotor fibres of sweat glands causes Frey's syndrome or gustatory sweating. Sweating occurs over the preauricular skin in response to stimulus to secrete saliva from the parotid.