What causes static electricity to build up on clothing?

Static electricity builds up on clothing through a process called triboelectric charging, which occurs when two different materials rub against each other and electrons transfer from one surface to the other. When fabrics like wool, nylon, or polyester rub together in a dryer or against your skin, one material gains electrons and becomes negatively charged while the other loses electrons and becomes positively charged. Synthetic fabrics are especially prone to this because they don't conduct electricity well, so the charge has nowhere to go and stays trapped on the surface. Low humidity makes the problem worse because dry air is also a poor conductor, preventing the static charge from gradually dissipating into the surrounding environment.