The voice is a delicate instrument that is affected by physical changes that occur throughout our lifespan. The vocal folds are made up of the vocalis muscle, otherwise known as the thyroarytenoid muscle, at its base. They are covered by the lamina propria, a connective tissue made up of three layers of collagen and elastin fibers, and surface mucosa, made up of squamous epithelial cells. These various tissue fibers provide a delicate balance of rigid structure and loose flexibility, which allow the vocal folds to stretch and move and then subsequently return to a baseline of 100-300 times per second. At rest, the vocal folds are in a relatively closed position. As pressure builds up beneath them, they reach a phonation threshold pressure which blows them apart. Bernoulli’s principle, which states that pressure in a space is decreased as the speed of fluid and air moving through it increases, comes into play and allows for the vocal folds to slam back shut.

The sound produced can then be adjusted as the folds are stretched and contracted by the movements of the thyroid, cricoid, and arytenoid cartilages. The farther they are stretched, the higher the tension and the higher the pitch. The quality of the sound is then further modified depending on the size, hydration, straightness of edges, and nervous control. The straighter the edges, hydration, and fine motor control, the more regular (periodic) and complete the focal folds move and the clearer the voice sound. As we age from infancy through old age, the physical features of our vocal tracts change, affecting the quality of sound that we produce.

The first major change occurs in early childhood. The infant vocal tract is designed for maximum airway protection and is physically closer to the vocal tract of other primates. To that end, the larynx and epiglottis are much higher in the throat so they can make contact with the soft palate and completely seal off entry of food and liquid to the airway. However, this structure limits the possibility range of sounds necessary for speech. As children age, their larynx drops and the angle of their vocal tract changes to a nearly 90-degree angle. With the descent of the larynx away from the soft palate, the vocal tract can accommodate all the resonances and dynamic variations necessary for the production of the many distinct speech sounds and resonances necessary for the full range of human language. Uniquely, evolution has favored communication over airway protection and safety in humans. Thus, the child’s voice becomes lower and more dynamic, capable of producing human speech where it was not able to before. However, despite this large physical shift, perceptually, the voice sounds largely the same.

The next major change, and the first truly audible one, occurs during puberty. Most notable in males, as testosterone increases, the laryngeal cartilages and vocal folds grow in size and length. With longer, thicker vocal folds and a larger resonant space disproportionate to the rest of the body, the biologically male voice drops in pitch significantly compared to the biologically female voice. Additionally, in both biological sexes, the lamina propria completes its differentiation into the three distinct layers discussed above, increasing flexibility and decreasing pitch while also adding to the richness of the voice.

The final major change, known as presbyphonia, occurs in old age. As we age, the collagen in our vocal folds stiffens, the mucosa dries and thins out, and the laryngeal cartilages ossify. These events decrease the flexibility and size of our vocal folds, which increases the pitch of the voice—like the tightening of a guitar string—in males. However, in female voices, the hormonal changes of menopause cause vocal fold edema, which enlarges the vocal folds enough to counteract these changes and deepen pitch. Moreover, as the vocal folds stiffen and dry out, they become less movable, which affects the regularity of the vocal fold closure. This, along with decreases in nervous innervation and motor control, leads to more air escape and irregular contacts between the vocal folds.

However, this is not a 100% given. Voice is also impacted by how it is used throughout a person’s lifetime. Unhealthy vocal habits, like smoking, not drinking enough water, and frequent shouting, can exacerbate the effects of age and misuse. Taking good care of the voice with exercise, good hydration, healthy breathing techniques, and gentle vocal behaviors can all help to minimize the effects of age on voice.

The hormonal differences in puberty result in the biological difference between male and female voices. For individuals transitioning from female to male, this change in vocal tract size can be improved with testosterone, which mimics the testosterone increase during puberty and can physically increase the size of the vocal tract cartilages and muscles. Hormones cannot reverse growth of these structures, however. For adults transitioning from male to female, behavioral voice treatment can help modify the voice. Surgical options include anterior commissure advancement, which shortens the portion of the vocal folds that can vibrate, and cricothyroid approximation, which pulls the thyroid away from the arytenoids to stretch the vocal folds at rest. Surgery is usually most effective in combination with voice therapy.

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