Generally as the rubber skin flexes, the stress causes it to dry and begin to crack. Figures that do not have a high degree of motion flexibility, such as the older A-1 series for President Lincoln, may only need to have their skin replaced every ten years. The most recent A-100 series human AAs, like the figure for President Barack Obama, also include flexion actuators that move the cheeks and eyebrows to permit more realistic expressions; however, the skin wears out more quickly and needs replacement at least every five years.