Concentration

When an effect has a duration of concentration, the effect lasts as long as you concentrate on it. Concentrating to maintain an effect is a standard action. Any factor that could break your concentration while you are performing activities that require focus (such as casting a spell) can also break your concentration while you’re maintaining an effect, causing the effect to end. See Concentration and Interrupted Spells on page 331 for more details. You can neither use an effect that requires concentration nor cast a spell while concentrating on an effect. Some effects last for a short time after you cease concentrating—typically 1 round per level, though individual effects may vary as noted in their descriptions.