The growth plates in feet stop growing sometime during the late teen years, but shoe size often continues to change over the course of a person's lifetime.
Although feet stop growing, shoe size can change due to several factors. One of the most common is age. The muscles that support the bones in the feet weaken with age, which can cause bones to move, making the foot bigger. Arches, for example, may collapse with age. Sometimes feet get wider, especially in people who run or are on their feet a lot.
Foot conditions, such as bunions, can also change a person's shoe size. A bunion is a bony growth at the bottom of the big toe. Wearing too-tight shoes often contributes to getting bunions. This is one of the reasons it is so important to wear shoes that fit.
Women often wear a bigger shoe size after pregnancy. The ligaments in the foot stretch as a result of pregnancy weight gain and the hormones produced to prepare the body for birth. This change is permanent, researchers say. Most women experience foot change only during their first pregnancy. A recent study found that up to 60 percent of women who have been pregnant say their shoe size has changed as an adult compared to only 13 percent of women who have not had children.