Signs and Symptoms
- Erythema (redness or flushing) and sweating in the cutaneous distribution of the auriculotemporal nerve
- Pain in the same area, often burning in nature
- Numbness or other altered sensations between attacks of pain
- Gustatory neuralgia may be present
- Discharge from the nose when smelling certain food

Causes
- Complication of surgeries near the parotid gland or injury to the auriculotemporal nerve
- Regeneration or nerve sprouting after endoscopic thoracic sympathectomy
- Accidental trauma, local infections, sympathetic dysfunction, or pathologic lesions within the parotid gland
- Ingrown hair follicle causing trauma or localised infection near the auriculotemporal nerve
- Switching of parasympathetic nerve fibers to a sympathetic response

Diagnosis
- Clinical signs and symptoms
- Starch-iodine test (Minor test) where iodine is applied to the face and starch turns blue in the presence of sweat
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Treatments
- Injection of botulinum toxin A
- Surgical transection of the nerve fibers (temporary treatment)
- Application of an ointment containing an anticholinergic drug
- Limited evidence supporting the effectiveness or safety of interventions
- Need for further clinical trials

Epidemiology
- Rare condition with unknown incidence
- Often occurs as a complication of parotidectomy
- Estimates suggest 30-50% of individuals develop Frey syndrome after parotidectomy
- Approximately 15% of affected individuals rate their symptoms as severe
- Affects males and females equally

Frey's syndrome (Wikipedia)

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Frey's syndrome (also known as Baillarger's syndrome, Dupuy's syndrome, auriculotemporal syndrome, or Frey-Baillarger syndrome) is a rare neurological disorder resulting from damage to or near the parotid glands responsible for making saliva, and from damage to the auriculotemporal nerve often from surgery.

Frey's syndrome
Other names	Auriculotemporal syndrome, Baillarger's syndrome, Dupuy’s syndrome, Frey-Baillarger syndrome
Redness associated with Frey's syndrome
Specialty	Neurology
Symptoms	Redness and sweating of cheek area when salivating
Causes	Damage to auriculotemporal nerve
Diagnostic method	Starch-iodine test
Frequency	30–50% (after parotidectomy)

The symptoms of Frey's syndrome are redness and sweating on the cheek area adjacent to the ear (see focal hyperhidrosis). They can appear when the affected person eats, sees, dreams, thinks about or talks about certain kinds of food which produce strong salivation. Observing sweating in the region after eating a lemon wedge may be diagnostic.