Static hair happens when hair becomes charged with electricity. All hair is made up of atoms, and atoms are compromised of protons, neutrons and electrons. Electrons move from one atom to another, and when they do this, the atoms become electrically charged. This causes static electricity in hair.
Dry hair is especially prone to static electricity. Blow-dried hair that is brushed out easily becomes statically charged. Dry hair attracts positive electric charges easier than wet hair does. Hair becomes more dry during cold winter months, so static electricity is often more prevalent then than during the summer.
A few steps can be taken to prevent static hair. Skipping a day in between shampoos helps reduce static, as washing strips the hair of natural oils that help to repel static. Conditioning also helps because it moisturizes the hair, which repels negative charges. For the same reason, hydrating shampoos help reduce static in hair as well.
Combing hair instead of brushing it also helps, as brushing causes friction between hair strands, which leads to static. Because the teeth on a comb are farther apart, less friction is placed on hair strands, reducing static. A simple metal barrette or bobby pin helps to prevent static electricity as well.