Implications of botulinum toxin injection of the brow∗

To the Editor: Botulinum toxin produces a more youthful appearance by smoothing facial wrinkles via the partial and temporary paralysis of selected facial muscles or muscle groups. The effects of paralyzing these muscles on one's nonverbal communication remain largely unexplored. Injecting the toxin into glabellar muscles diminishes the appearance of frown lines but also suppresses the mobility and, presumably, the expressiveness of the eyebrows.

In The Expression of Emotions in Man and Animals, Charles Darwin1 wrote about human emotions signaled by eyebrow movements. Among these are despair and dejection, indicated by bringing together and elevating the inner eyebrows, and surprise and fear, signaled by elevating the entire brow. Darwin emphasized the human ability to create vertical brow furrows by contracting glabellar muscles to lower and approximate the eyebrows. He argued that the frown was the expression “ … of something difficult or displeasing encountered in a train of thought or in action,”1 and considered it one of man's most important expressions. Darwin's observations on the universality of eyebrow movements as part of nonverbal communication have been largely validated and expanded by more recent authors. Stanford University psychologist Paul Ekman describes 3 distinct eyebrow actions used to express emotion and provide nonverbal conversational signals. These 3 movements, governed by glabellar contractions, are used individually or in concert to express sadness, fear, surprise, anger, or distress. When used with speech, these movements punctuate spoken words, emphasizing the intended message; used without speech, they can communicate greeting, affirmation or negation, and skepticism. In contrast to the frown, a quickly raised brow, or “eyebrow flash,” is employed widely across cultures to convey emotional or conversational meaning through facial context, usually accompanying a positive signal, such as a smile.2, 3 The emotional signals provided by the eyebrows appear to be universal,2 which may imply that these signals are advantageous to the human species, both in communicating meaning and in providing a means to interpret signals (Fig 1).

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Fig 1. John Singer Sargent (1856-1925), Lady Agnew of Lochnaw, 1892. Observer's gaze is drawn to the lady's eyes, where her expression is framed and punctuated by a raised brow. Sir Charles Bell (1774-1842, anatomist, surgeon, and physiologist, best known for defining different functions for ventral and dorsal spinal roots, as well as for characterizing the facial nerve palsy bearing his name) regarded the corrugator muscle as “the most remarkable muscle of the human face. It knits the eyebrows with an energetic effort, which unaccountably, but irresistibly, conveys the idea of mind.”1 Image reprinted courtesy of the National Gallery of Scotland.

Considering the brow's importance to communicating emotion, one may question the practice of partially immobilizing its musculature for cosmetic effect. Injection of the glabellar muscles, while lessening forehead and brow wrinkles, also reduces the patient's ability to either elevate the eyebrows or bring them together in a frown.4 Although botulinum toxin injection impairs brow mobility, little has been written on its effects on patients' interpersonal relationships. Although patients receiving botulinum toxin injections may appear happier and more youthful—and perhaps gain confidence in their self images—they may also experience a reduction in their ability to express emotions (particularly fear, anger, and sadness)5 or to communicate nonverbally. No studies have yet examined these effects on patients or the corresponding reactions of others to one's diminished expressivity. Research in this area may help refine the patient selection process for botulinum cosmesis; for example, patients whose vocations depend on interpersonal communication might decline botulinum injections or choose alternative cosmetic therapy. Postinjection expressiveness, rather than wrinkle reduction alone, could become an additional outcome measure for physicians providing botulinum therapy.