Exposure to high noise levels, even for short periods, can cause temporary or permanent hearing loss. Noise damages the inner ear's hearing mechanism by changing air pressure. In addition to hearing damage, noise makes communication difficult and reduces efficiency by disturbing sleep and causing tiredness and irritability. The World Health Organization recommends noise level guidelines to prevent annoyance and allow undisturbed sleep. Physical effects of noise include constricted blood vessels and increased blood pressure. At work, noise can reduce concentration and safety. Hearing damage from loud noise is preventable through good management, though individuals' sensitivity to noise varies. A person's ears cannot distinguish between noise from work or leisure in terms of damage.