Vocal hygiene has been part of the voice treatment literature continuously since the publication of Mackenzie's The Hygiene of Vocal Organs, in 1886. In it the author, a noted otolaryngologist, described many magical prescriptions used by famous singers to care for their voices. In 1911, a German work by Barth included a chapter with detailed discussion of vocal hygiene. The ideas about vocal hygiene expressed in this book were similar to those expressed in the current literature. Concern was raised about the effects of tobacco, alcohol, loud and excessive talking, hormones, faulty habits, and diet on the voice. Another classic text was Diseases and Injuries of the Larynx, published in 1942. The authors, Jackson and Jackson, implicated various vocal abuses as the primary causes of voice disorders, and cited rest and refraint from the behavior as the appropriate treatment. Luchsinger and Arnold (1965) stressed the need for attention to the physiological norm as the primary postulate of vocal hygiene and preventive laryngeal medicine. Remarkably, these authors discussed the importance of this type of attention not only for teachers and voice professionals, but also for children in the classroom. Subsequently, virtually all voice texts have addressed the issue of vocal hygiene.

Both the general public and professionals in numerous disciplines commonly use the term hygiene. The 29th edition of Dorland's Medical Dictionary defines it as “the science of health and its preservation.” Thus, we can take vocal hygiene to mean the science of vocal health and the proper care of the vocal mechanism. Despite long-held beliefs about the value of certain activities most frequently discussed as constituting vocal hygiene, the science on which these ideas are based was, until quite recently, more implied and deduced than specific.

Patient education and vocal hygiene are both integral to voice therapy. Persons who are educated about the structure and function of the phonatory mechanism are better able to grasp the need for care to restore it to health and to maintain its health. Thus, the goal of patient education is understanding. Vocal hygiene, on the other hand, focuses on changing an individual's vocal behavior. In some instances, a therapy program may be based completely on vocal hygiene. More frequently, however, vocal hygiene is but one spoke in a total therapy program that also includes directed instruction in voice production techniques.

Although there are commonalities among vocal hygiene programs regardless of the pathophysiology of the voice disorder, that pathophysiology should dictate some specific differences in the vocal hygiene approach. In addition to the nature of the voice disorder, factors such as timing of the program relative to surgery (i.e., pre or post), and whether the vocal hygiene training stands alone or is but one aspect of a more extensive therapy process, must also inform specific aspects of the vocal hygiene program.

Hydration and environmental humidification are particularly important to the health of the voice, and, as such, should be a focus of all vocal hygiene programs. A number of authors have studied the effects of hydration and dehydration of vocal fold mucosa and viscosity of the folds on phonation threshold pressure (PTP). (PTP is the minimum subglottal pressure required to initiate and maintain vocal fold vibration.) For example, Verdolini et al. (1990, 1994) studied PTP in normal speakers subjected to hydrating and dehydrating conditions. Both PTP and self-perceived vocal effort were lower after hydration. Jiang, Ng, and Hanson (1999) showed that vocal fold oscillations cease in a matter of minutes in fresh excised canine larynges deprived of humidified air. Rehydration by dripping saline onto the folds restored the oscillations, demonstrating the need for hydration and surface moisture for lower PTP.

In one light, viscosity is a measure of the resistance to deformation of the vocal fold tissue. Viscosity is increased by hydration and decreased by drying—hence the importance of vocal fold hydration to ease of phonation. Moreover, it appears that the body has robust cellular and neurophysiological mechanims to conserve the necessary hydration of airway tissues. In a study of patients undergoing dialysis, rapid removal of significant amounts of body water increased PTP and was associated with symptoms of mild vocal dysfunction in some patients. Restoration of the body fluid reversed this trend (Fisher et al., 2001). Jiang, Lin, and Hanson (2000) noted the presence of mucous glands in the tissue of the vestibular folds and observed that these glands distribute a very important layer of lubricating mucus to the surface of the vocal folds. Environmental hydration facilitates the vocal fold vibratory behavior, mainly because of the increased water content in this mucous layer and in the superficial epithelium. The viscosity of secretions is thickened with ingestion of foods or medications with a drying or diuretic effect, radiation therapy, inadequate fluid intake, and the reduction in mucus production in aging.

Thus, there appear to be a number of mechanisms, not yet fully understood, by which the hydration of vocal fold mucosa and the viscosity of the vocal folds are directly involved in the effort required to initiate and maintain phonation. Both environmental humidity and surface hydration are important physiological factors in determining the energy needed to sustain phonation. External or superficial hydration may occur as a by-product of drinking large amounts of water, which increases the secretions in and around the larynx and lowers the viscosity of those secretions. Steam inhalation and environmental humidification further hydrate the surface of the vocal folds, and mucolytic agents may decrease the viscosity of the vocal folds. Clearly, the lower the phonation threshold pressure, the less air pressure is required and the greater is the ease of phonating. Many questions remain in this area, such as the most effective method of hydration.

Other major components of vocal hygiene programs are reducing vocal intensity by eliminating shouting or speaking above high ambient noise levels, avoiding frequent throat clearing and other phonotraumatic behaviors. The force of collision (or impact) of the vocal folds has been described by Titze (1994) as proportional to vibrational amplitude and vibrational frequency. This was explored further in phonation by Jiang and Titze (1994), who showed that intraglottal contact increases with increased vocal fold adduction. Titze (1994) theorized that if a vibrational dose reaches and exceeds a threshold level in a predisposed individual, tissue injury will probably ensue. This lends support to the widespread belief that loud and excessive voice use, and indeed other forms of harsh vocal productions, can cause vocal fold pathology. It also supports the view that teachers and others in vocally demanding professions are prone to vibration overdose, with inadequate recovery time. Thus, the stage is set for cyclic tissue injury, repair, and eventual voice or tissue change.

The complexity of vocal physiology suggests a direct connection between viscosity and hydration, phonation threshold pressure, and the effects of collision and shearing forces. The greater the viscosity of vocal fold tissue, the higher the PTP that is required and the greater is the internal friction or shearing force in the vocal fold. These effects may explain vocal fold injuries, particularly with long-term vocal use that involves increased impact stress on the tissues during collision and shearing stresses (Jiang and Titze, 1994). Thus, issues of collision and the impact forces associated with increased loudness and phonotraumatic vocalization are appropriately addressed in vocal hygiene programs and in directed therapy approaches.

Reflux, both gastroesophageal and laryngopharyngeal, affects the health of the larynx and pharynx. Gastric acid and gastric pepsin, the latter implicated in the delayed healing of submucosal laryngeal injury (Koufman, 1991), have been found in refluxed material. Laryngopharyngeal reflux has been implicated in a long list of laryngeal conditions, including chronic or intermittent dysphonia, vocal fatigue, chronic throat clearing, reflux laryngitis, vocal nodules, and malignant tissue changes. Treatment may include dietary changes, lifestyle modifications, and medication. Surgery is usually a treatment of last resort. Caffeine, tobacco, alcohol, fried foods, and excessive food intake have all been implicated in exacerbating the symptoms of laryngopharyngeal reflux. Thus, vocal hygiene programs that address healthy diet and lifestyle and that include reflux precautions appear to be well-founded. It is now common practice for patients scheduled for any laryngeal surgery to be placed on a preoperative course of antireflux medication that will be continued through the postoperative healing stage. Although this is clearly a medical treatment, the speech-language pathologist should provide information and supportive guidance through vocal hygiene instruction to ensure that patients follow the prescribed protocol.

An unanswered question is whether a vocal hygiene therapy program alone is adequate treatment for vocal problems. Roy et al. (2001) found no significant improvement in a group of teachers with voice disorders after a course of didactic training in vocal hygiene. Teachers who received a directed voice therapy program (Vocal Function Exercises), however, experienced significant improvement. It should be noted that the vocal hygiene program used in this study, being purely didactic and requiring no activity on the part of the participants, might more appropriately be described as a patient education program. Chan (1994) reported that a group of non-voice-disordered kindergarten teachers did show positive behavioral changes following a program of vocal education and hygiene. In another study, Roy et al. (2002) examined the outcome of voice amplification versus vocal hygiene instruction in a group of voice-disordered teachers. Most pairwise contrasts directly comparing the effects of the two approaches failed to reach significance. Although the vocal hygiene group showed changes in the desired direction on all dependent measures, the study results suggest that the benefits of amplification may have exceeded those of vocal hygiene instruction. Of note, the amplification group reported higher levels of extraclinical compliance with the program than the vocal hygiene group. This bears out the received wisdom that it is easier to take a pill—or wear an amplification device—than to change habits.

Although study results are mixed, there is insufficient evidence to suggest that vocal hygiene instruction be abandoned. The underlying rationale for vocal hygiene is sufficiently compelling that a vocal hygiene program should continue to be a component of a broad-based voice therapy intervention.