The human foot is a complex structure composed of 26 bones, 33 joints, and over 100 muscles, tendons, and ligaments that support the body’s weight and facilitate movement. While many believe feet continue to grow throughout adulthood, the bony structure of the foot is fixed after adolescence. Changes in adult foot size are not due to bone growth but rather to alterations in the surrounding soft tissues and mechanical structure. The foot’s ultimate length is determined by skeletal maturity, but its overall size and shape can be influenced by various factors over time.
When Skeletal Growth Stops
The true growth in the length of the foot, driven by bone elongation, ceases when the skeletal system reaches full maturity. This process is governed by the fusion of growth plates (epiphyseal plates), which are areas of cartilage near the ends of long bones. During childhood and adolescence, these plates create new bone tissue, allowing the bones of the feet and legs to lengthen.
The timing of this skeletal closure varies between sexes. In females, growth plates typically fuse between the ages of 13 and 15, with complete fusion often occurring by age 17. For males, this process occurs later, usually between the ages of 15 and 17, with complete fusion around age 20 or 21. Once the growth plates fully harden into solid bone, the foot’s bones can no longer increase in length.
The growth plates in the feet and ankles are among the first to fuse. Although the feet stop lengthening, the bones may continue to gain density and mass for a few years afterward. The fundamental size set during the late teens and early twenties remains the bony limit for the foot’s length.
Why Adult Feet Change Size
Even though the bones stop lengthening, adult feet often change size, leading many to believe they are still growing. This change is typically a gradual increase in width and flatness, resulting from the cumulative stress of walking and weight-bearing over decades. This structural change is often described as the foot “settling” or spreading.
Loss of Elasticity
A primary cause is the natural loss of elasticity in the tendons and ligaments that support the foot’s arches, a process that accelerates with age. As these soft tissues become less taut, the arch gradually flattens, causing the foot to lengthen and widen slightly. This subtle collapse can necessitate moving up a half-size or even a full shoe size.
Weight Gain
Increased body weight contributes significantly to changes in adult foot size. Gaining weight places greater mechanical pressure on the arches, stressing the supportive ligaments and exacerbating arch flattening and spreading.
Hormonal Changes
Hormonal changes, particularly during pregnancy, can lead to permanent changes in foot size for some women. The hormone relaxin, released during pregnancy to loosen the ligaments in the pelvis in preparation for childbirth, acts systemically throughout the body, including the feet. When relaxin causes the ligaments in the foot to become lax, the arch can flatten under the increased weight of pregnancy, sometimes resulting in a lasting increase in foot length and width.
The Role of Arch Structure and Genetics
The final size and shape of a person’s foot are largely dictated by their genetic blueprint, which determines bone dimensions and arch type. Genetics influence whether an individual is predisposed to having a high arch, a low arch, or a flat foot, establishing the parameters of the foot’s architecture.
Maintaining the foot’s size and shape relies heavily on the integrity of its three arches: the medial longitudinal, lateral longitudinal, and transverse arches. These arches act as shock absorbers and force distributors, supported by strong connective tissue like the plantar fascia. The plantar fascia is a thick band of tissue running along the bottom of the foot, functioning like a tie-rod to maintain the arch’s height and prevent elongation when bearing weight.
The gradual breakdown of this supportive structure—the loss of elasticity in the ligaments and the stretching of the plantar fascia—is what leads to the adult foot becoming longer and wider. The structural components determined by genetics are constantly challenged by the forces of gravity and body weight. When the soft tissues can no longer withstand this pressure, the foot’s shape changes, even though the underlying bones have not grown.