Whether one should breathe through the mouth or the nose when singing or speaking is a matter of great contention.
Inside your nasal cavities, the nasal turbinates are highly irrigated by blood vessels inside them. In fact, it’s the dilation of these blood vessels that sometimes causes your nose to congest. However, they also have a very important function: they warm the air you breathe in as it passes above, between, around and under them, causing moisture from the walls of the turbinates to evaporate and therefore increase the humidity of the inhaled air. So, when you inhale through the mouth, the air is not going to be heated to the same extent and it’s not going to be as humidified.
There are two types of hydration when it comes to the larynx, the organ which houses the vocal folds: superficial hydration, which concerns the fluid over the vocal fold and laryngeal surfaces; and systemic hydration, which concerns the fluid within the body and vocal folds.
Dehydration may be superficial, and therefore result from more temporary, localized settings, such as being at the beach or running against the wind, or systemic, and therefore less temporary because it reflects the amount of water in your body. The use of clean steamers and nebulizers will only increase superficial hydration, not systemic hydration.
We must also explore phonation threshold pressure (PTP), defined as the lowest subglottic pressure (pressure under the vocal folds) required to initiate and sustain vocal fold oscillation. PTP is considered a measure of ease of phonation and an indicator of vocal fold health. By increasing the viscosity of the vocal folds, in general, dehydration increases PTP, making it harder to initiate and sustain phonation, and may also decrease vocal range.
In summary: dehydration reduces the stability and ease of phonation. In the long term, it may also contribute to vocal disorders. For example, superficial dehydration increases jitter and shimmer in the voice, which are irregular fluctuations in pitch and intensity, respectively.
As you’ll learn by reading our encyclopedia article about the Power-Source-Filter model of voice production, the vocal folds have multiple layers. In general, they can be divided into two: the body, which is located deeper and includes the vocalis muscle, and the cover, which is more superficial. To avoid confusion, keep in mind that there’s also a three-layer model for the structure of the vocal folds.
Intuitively, dry air is more likely to decrease superficial hydration, by sucking water from the cover and overlying mucus covering, and not the deeper body of the vocal folds. This may be part of the reason why superficial dehydration affects the laryngeal vibratory mechanism M2 more than M1.
However, nasal breathing takes longer for the same volume of air. This disparity is especially pronounced in people with allergies, turbinate hypertrophy or a deviated septum because their small nasal cavities allow less (or no) air to pass through in each second. Consult with your doctor to know what steps could be taken to minimize or solve these issues if they’re significant to you.
So, no matter if you’re a singer, a public speaker or a voice actor, one must find a compromise: to breathe through the mouth whenever there’s not enough time to breathe through the nose.
Elena Stevens, M. (2017). Examining the Reversal of Vocal Fold Dehydration Using Aerosolized Saline in an Excised Larynx Model BYU ScholarsArchive Citation [Brigham Young University]. https://scholarsarchive.byu.edu/etd
Hemler, R. J. B., Wieneke, G. H., Lebacq, J., & Dejonckere, P. H. (2001). Laryngeal mucosa elasticity and viscosity in high and low relative air humidity. European Archives of Oto-Rhino-Laryngology, 258(3), 125–129. https://doi.org/10.1007/s004050100321
King, R. E., Steed, K., Rivera, A. E., Wisco, J. J., & Thibeault, S. L. (2018). Magnetic resonance imaging quantification of dehydration and rehydration in vocal fold tissue layers. PLOS ONE, 13(12), e0208763. https://doi.org/10.1371/journal.pone.0208763
Mahalingam, S., & Boominathan, P. (2016). Effects of steam inhalation on voice quality-related acoustic measures. The Laryngoscope, 126(10), 2305–2309. https://doi.org/10.1002/lary.25933
Sivasankar, M., & Leydon, C. (2010). The role of hydration in vocal fold physiology. In Current Opinion in Otolaryngology and Head and Neck Surgery (Vol. 18, Issue 3, pp. 171–175). Lippincott Williams and Wilkins. https://doi.org/10.1097/MOO.0b013e3283393784
VaréGne, P., Ferrus, L., Manier, G., & Gire, J. (1986). Heat and water respiratory exchanges: comparison between mouth and nose breathing in humans. Clinical Physiology, 6(5), 405–414. https://doi.org/10.1111/j.1475-097X.1986.tb00071.x
Zou, Z. fei, Chen, W., Li, W., & Yuan, K. (2019). Impact of Vocal Fold Dehydration on Vocal Function and Its Treatment. Current Medical Science, 39(2), 310–316. https://doi.org/10.1007/s11596-019-2036-0