The risk is higher if you exercise, sweat heavily, or wear tight synthetic fabrics, since heat and friction can irritate the skin and increase the chance of rashes or infections.
Breathable fabrics such as cotton, regular showers, and changing underwear after workouts can greatly reduce these problems and help keep the skin dry.
Occasionally rewearing underwear in a low-sweat situation is unlikely to cause serious harm, but wearing a fresh pair each day remains the simplest and healthiest habit.
