Frey Syndrome: Why You May Be Sweating After Eating

Frey syndrome is also known as gustatory sweating or gustatory hyperhidrosis

parotid
Frey syndrome involves the parotid glands. Getty Images

After eating hot and spicy foods, some people sweat from the face—the lips, forehead, nose, and scalp. For many, this trigeminovascular reflex is completely normal.

However, sweating from the face after eating any type of food is indicative of a condition called gustatory sweating, or gustatory hyperhidrosis. Moreover, this onset of sweating may come about not only from the actual chewing of food but also from either thinking or talking about food.

Common symptoms of gustatory sweating include sweating, flushing, redness, and general discomfort felt at cheek level. More uncommonly, people with this condition feel warmth or pain with chewing.

Gustatory sweating can be very uncomfortable and substantially impact a person’s quality of life. According to Sood and co-authors, gustatory sweating “can cause considerable social incapacity ranging from the need for regular mopping to being virtually house-bound.” In other words, the constant need to “mop” away sweat may make it difficult for some to leave the house.

The most common iteration of gustatory hyperhidrosis is Frey syndrome. Frey syndrome refers to a sweating and flushing along the distribution of the auriculotemporal nerve. The auriculotemporal nerve provides sensation to the side of the head. Frey syndrome is also called gustatory hyperhidrosis of the cheek.

What Is Frey Syndrome?

Frey syndrome is rare, with fewer than 20,000 Americans diagnosed each year.

Essentially, Frey syndrome results from faulty rewiring of the nerves responsible for salivation, sweating, and flushing. It is named after French neurologist Lucia Frey, who described the condition as “auriculotemporal nerve syndrome” in 1923.

Frey published a report detailing her eponymous illness after treating a Polish soldier who experienced gustatory sweating after sustaining an infected bullet wound affecting the parotid gland.

The parotid gland is the largest of the salivary glands and is located at the level of the cheek. It secretes saliva, which helps digest and moisten food. Although Frey wasn’t the first physician to take note of the condition, she was the first to implicate the auriculotemporal nerve in the development of this disease.

The release of saliva by the parotid gland is mediated by a complex reflex arc that involves the auriculotemporal nerve. In people with Frey syndrome, after an injury to the auriculotemporal nerve, this nerve regenerates abnormally. Instead of only providing parasympathetic innervation to the parotid gland, which would result in normal salivation after introduction of food, the parasympathetic fibers of the auriculotemporal nerve also regenerate to provide innervation to sweat glands and subcutaneous blood vessels, resulting in sweating and flushing, respectively. Normally, this sweating and flushing is under sympathetic control.

In other words, after the auriculotemporal nerve is injured, its parasympathetic fibers regrow to not only control salivation but also control sweating and flushing after a person is stimulated with food. Moreover, in some people, this asymmetric pattern of sweating can extend past the face altogether and affect the trunk, arms, and legs.

The more body surface area affected, the more severe the symptoms.

Causes

Anything that damages the auriculotemporal nerve can result in Frey syndrome, including the following:

  • Parotid gland surgery (biggest cause)
  • Blunt trauma to the cheek
  • Neck surgery
  • Chronic infection of the parotid area
  • Mandibular fracture
  • Fracture of the temporomandibular joint
  • Surgery to the temporomandibular joint
  • Removal of the submandibular glands
  • Removal of the thyroid gland
  • Thoracic sympathectomy (a surgery done to control sweating)
  • Birth trauma or injury following forceps delivery (in infants)

In the 1940s, parotid gland surgery was popularized in the United Kingdom to treat a wide variety of conditions, both cancerous and noncancerous.

Gustatory sweating along with several other adverse effects, including facial nerve injury, decreased facial sensation, salivary fistula, hematoma, and keloids were commonly observed among patients who received parotid gland surgery. Of note, people who have their entire parotid gland removed are more likely to experience Frey syndrome than are those who have only part of the parotid gland removed.

Frey syndrome can also be seen with the other following neurological conditions:

  • Facial herpes zoster
  • Chorda tympani injury
  • Cluster headache
  • Diabetic neuropathy
  • Encephalitis
  • Syringomyelia
  • Tumor in the cervical sympathetic trunk

Most people who experience gustatory sweating aren’t bothered by it—only between 10 and 15 percent of people who experience it seek medical attention. Furthermore, after parotid surgery, only 10 percent of patients report symptoms indicative of this condition. However, on further questioning, 30 to 50 percent of patients will admit to symptoms of gustatory sweating. Frey syndrome usually appears between 1 and 12 months after surgery.

Frey syndrome can happen to people at any age. Nevertheless, it is rare in infants and children who only really ever experience injury to the parotid area after forceps delivery, and injury from forceps delivery is rare.

In children, food allergy can be mistaken for Frey syndrome. However, the symptoms of food allergy occur after the ingestion of food not during chewing.

Diagnosis

The easiest way to diagnose Frey syndrome involves the application of iodinated starch (indicator) powder to the face. This procedure is called the Minor test. The patient is then given lemon sweets or some other sweet food to stimulate sweating. Affected areas where sweat droplets form turn blue-black. The droplets can be easily wiped away from the face so that the test may be repeated. This test can also be used to test for Frey syndrome in people without symptoms (i.e., asymptomatic patients).

Although this test is accurate, it will not demonstrate the severity of the condition. Furthermore, this test carries the potential risk of inhalation of the starch powder. This test should be administered on dry skin, and shouldn’t be used in people who perspire heavily.

Another more expensive and involved diagnostic test to determine whether a person has Frey syndrome involves a biosensoring method that utilizes enzymatic electrodes that detect L-lactate levels on the skin.

A more rudimentary test for Frey syndrome involves the application of one-ply tissue paper to the face to check for sweating after the patient is stimulated with a sweet food.

Finally, infrared medical thermography can be used to visualize Frey syndrome. This diagnostic test requires that the temperature and humidity in the room be constant. First, after stimulation, a hot spot is visualized that corresponds to the dilation of subcutaneous blood vessels. Second, a cold spot is visualized that represents gustatory sweating. These changes are harder to visualize in people with darker skin.

Treatment

In most people, Frey syndrome goes away on its own within a period of at most 5 years. People with mild symptoms should be reassured that the condition will pass on its own without treatment.

In those who are seriously impacted by the condition, gustatory sweating is commonly the most distressing symptom and prompts a person to seek help.

Botox

Recent evidence-based research points to Botox therapy as that most promising and successful way to treat the gustatory sweating and flushing of Frey syndrome. More specifically, Botox therapy has proven to be 98 percent effective in treating symptoms of gustatory sweating. Botox therapy has also proven effective in people who experience gustatory sweating secondary to diabetic neuropathy, a type of nerve damage due to diabetes.

In a 2017 article, Lovato and co-authors write the following:

BTX [Botox] therapy is highly successful in the treatment of gustatory sweating (Frey syndrome), and could be considered the gold standard treatment for this post-parotidectomy complication.

When treating Frey syndrome with Botox therapy, a clinician must first identify the area affected by means of the Minor test. This area is then divided into several smaller squares, which are between 1 and 1.5 cm. Botox is then injected into each of these squares to elicit a diffuse, uniform effect.

Notably, other treatments of Frey syndrome have been tried. For the most part, these treatments provide limited or no relief.

Antiperspirants

First, antiperspirants have been applied to the area affected by gustatory sweating. Some patients have reported limited relief for a period of several weeks thanks to antiperspirants. For best results, a gel form of the antiperspirant is applied at night to dry skin and washed away in the morning. A hairdryer can be used to dry the antiperspirant after application.

For a period of 12 hours after application, the patient should avoid shaving the treated area. Over time, as gustatory sweating runs its course and resolves on its own, fewer dosages of antiperspirants can be used, and patients won’t need to apply antiperspirants daily. Of note, antiperspirants can act as skin irritants and lead to inflammation. Caution should also be taken to avoid introduction of the antiperspirant into the eye.

Topical Anticholinergics

Second, topical anticholinergics have been used to treat Frey syndrome. These anticholinergics include scopolamine, glycopyrrolate, and diphemnanilmethylsulfate and can be applied as roll-on solutions or creams. Anticholinergics can improve symptoms for about 3 days.

Importantly, anticholinergics are absorbed by the skin and could cause systemic adverse effects including dry mouth, blurred vision, itchy eyes, urinary retention, increased heart rate, and allergies. Furthermore, anticholinergics should not be used in people with glaucoma, diabetes mellitus, thyroid disease, obstructive uropathy, as well as hepatic, renal, cardiovascular or central nervous disease.

Surgical Options

Third, surgery has been unsuccessfully attempted to attenuate the symptoms of Frey syndrome. These surgeries include cervical sympathectomy, tympanic neurectomy, sternocleidomastoidtransfer transfer, and dermis-fat grafts. Additionally, various materials and interpositional barriers have been used to treat gustatory sweating.

Understandably, most people who develop gustatory sweating secondary to surgery are reluctant to receive more surgery to treat this condition.

Sources::

Disorders Of Sebaceous, Eccrine and Apocrine Glands. In: Wolff K, Johnson R, Saavedra AP, Roh EK. eds. Fitzpatrick's Color Atlas and Synopsis of Clinical Dermatology, 8e New York, NY: McGraw-Hill.

Fealey RD, Hebert AA. Chapter 84. Disorders of the Eccrine Sweat Glands and Sweating. In: Goldsmith LA, Katz SI, Gilchrest BA, Paller AS, Leffell DJ, Wolff K. eds. Fitzpatrick's Dermatology in General Medicine, 8e New York, NY: McGraw-Hill; 2012.

Lovato, A, et al. Botulinum toxin therapy: functional silencing of salivary disorders. Acta Otorhinolaryngologica Italica. 2017;37:168-171 

Sood S, Quraishi MS, Bradley PJ. Frey syndrome and parotid surgery. Clinical Otolaryngology. 1998; 23: 291-301.

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