Introduction

Frey syndrome (sometimes called gustatory sweating) is a rare condition that causes you to sweat when eating or thinking about food. While it is not life-threatening, depending on the severity of the condition, it can be uncomfortable and negatively impact your quality of life.

The condition typically arises due to damage to nerves associated with the parotid gland. This damage could be caused by trauma, but more often is due to surgery. Frey syndrome occurs in patients who have undergone a parotidectomy typically.  

The parotid glands are located under your ears and are responsible for saliva production. A parotidectomy is a procedure to remove these glands. Other surgeries related to the jaw or parotid region, as well as infection and general trauma to the area, carry a risk of subsequent Frey syndrome development, but parotidectomy is the most common cause. 

Pathophysiology of frey syndrome

The exact cause of Frey syndrome is not well understood. Saliva plays an important role in eating and digestion. When thinking about eating or you are about to eat, nerves stimulate your salivary glands to produce saliva. When these nerves are damaged it can cause Frey syndrome.

When these nerves heal or regenerate, they do so aberrantly and connect to nearby sweat glands, so the nerves are still triggered by eating or thoughts about food, but they now stimulate the sweat glands instead.¹

The intensity and debut of symptoms can vary greatly between patients. Symptoms can occur immediately post-surgery or could develop months or even years later. It can also be inconsequential to your daily life, with mild symptoms and some discomfort, but unfortunately for some, the sweating can be frequent and severe, notably diminishing their quality of life. 

Prognosis and long-term outcomes

The exact prognosis can vary and depends on the course and extent of the nerve damage. The reported rates of Frey syndrome following a parotidectomy vary a lot, from 5% to as high as 100%.^2,3 The wide range of reported figures can be explained by the wide variability in symptom severity and reporting, and the lack of standardised diagnosis methods.¹ The higher-end range may also be attributed to a lack of preventive measures.

Quality of life

Fortunately, in most cases, Frey syndrome is mild and not life-threatening. However, its psychological and social implications on your day-to-day life can be felt deeply. The impact on your quality of life should be seriously considered when treating and managing the case. 

Patients are likely to experience feelings of embarrassment due to excessive sweating in social situations. Of course, this is particularly troublesome for social situations that involve food or eating. In severe cases, the fear of triggering symptoms in public can lead to reduced social interactions and even social isolation. 

Indeed, impacts on quality of life due to Frey syndrome have been reported. Negative self-esteem due to the condition has been reported as persisting as long as 5 years after the onset and the condition is also correlated with decreased social satisfaction.^4,5 

However, for many patients, symptoms and their impact are mild. The large variability in how the condition develops emphasises the need for individualised approaches in treatment.

Recurrence and persistence of symptoms 

A notable concern with Frey syndrome is that the symptoms can recur over time and become chronic. Although the severity can lessen over time, it can persist and even worsen in some. Patients may continue to experience symptoms five years after the initial surgery.⁴

Severe and long-term symptoms are associated more with patients who underwent more substantial surgical procedures and who didn't receive preventive treatment. 

Effectiveness of long-term treatments

There are multiple treatments available for patients with Frey syndrome, but they vary in their invasiveness and long-term effectiveness. Patient outcomes and satisfaction depend on their response to treatment and the initial severity of their condition. 

Botulinum toxin injections 

This is one of the most common treatment options and involves injecting small amounts of botulinum toxin (often known by the brand name botox) into the affected sites. It works by preventing the stimulation of the sweat glands.

Despite the term toxin in the name, this procedure is safe and generally is not associated with serious side effects. However, it should be administered by a trained health care professional only. Although botulinum toxin is commonly used in purely cosmetic treatments, it also has medical applications, such as treating Frey syndrome. 

Botulinum toxin can be an effective treatment, with symptoms and quality of life improving about 4-7 days post-application. However, It is only a short-term treatment, so repeat injections are required. Symptoms can recur in up to 27% of patients one year post-treatment, and 92% of patients 3 years post-treatment. That said, repeated injections are not harmful and can be used to extend the effectiveness of the treatment, although, unfortunately, some patients become resistant to the treatment over time.^1,8

Generally, botulinum toxin is an effective treatment for Frey syndrome and is associated with improved quality of life.

Surgical interventions

Surgical intervention can be considered if symptoms are severe, persistent, and resistant to other treatment options. This can involve implementing some form of barrier to stall the aberrant regeneration of the damaged nerve that causes Frey syndrome. Other options may be to cut the nerves or to remove the affected skin and then graft the affected area.¹

Whether surgery is performed should be considered on a case-by-case basis, effectiveness and subsequent recovery can vary significantly depending on the patient and the surgical procedure used, and risks to health and cosmetics can be significant. For many, the risks and potential outcomes are not worth it. It is essential to have a thorough consultation with a healthcare specialist if considering surgery to treat Frey syndrome, and typically should be reserved for severe cases.¹

Topical antiperspirants

There is evidence that topical antiperspirants can reduce symptoms of Frey syndrome. The topical application of glycopyrrolate can be used as a short-term treatment, with a single application being effective for several days. Other commercial antiperspirants are, unfortunately, not useful.^3,6

Factors influencing long-term outcomes

The initial cause of Frey syndrome, as well as what treatment options are pursued and a patient's attributes can determine the long-term outcomes of Frey syndrome.

Extent of initial surgery

Frey syndrome is most commonly caused by nerve damage as a result of a surgical procedure, the extent of the surgery is perhaps the most significant determining factor in the long-term outcomes of Frey syndrome. The larger the scale of the surgery, such as a total parotidectomy, the greater the risk of developing symptoms.⁷ 

Preventive measures taken during surgery can significantly influence the risk of developing the condition and subsequent severity of symptoms.

Patient characteristics 

Patient attributes, such as age and overall health, can influence the prognosis and long-term outcomes of Frey syndrome. Older individuals may have a lesser capacity for nerve regeneration, and so are actually at a lesser risk of developing symptoms. The nerves are less likely to regenerate aberrantly if they have a reduced ability to regenerate in the first place.

Another determining factor could be the patient's sweat glands sensitivity pre-Frey syndrome onset. Patients who sweat more easily may experience more severe symptoms from the onset of the condition. 

Summary

Frey syndrome is complex, it can be caused by multiple different surgeries affecting your salivary glands, post-infection, or post-trauma to the region. The primary symptom is excessive sweating when eating or thinking about food. Amongst patients with the condition, there is a wide variety in the severity of symptoms and long-term outcomes. For some patients, the condition can improve with time, while for others it can worsen. Due to the potentially embarrassing nature of the symptoms, it can pose significant quality-of-life implications for patients and should be taken seriously. 

There are effective treatment options, such as botulinum toxin injections, and many patients experience improvement in symptoms with this treatment. The exact prognosis varies between individuals and is determined by the type and extent of surgery that caused the condition, the trauma, or the infection if that was the aetiology. It is also influenced by the treatment type and the individual’s characteristics. 

Effective treatment is dependent on a thorough personalised consultation with a healthcare professional.