But if you're a senior citizen, hot weather can be much more than just a nuisance. The body's natural defenses against heat can break down with age, putting seniors at risk for heat stroke, heat exhaustion, and other serious disorders. Several factors make senior citizens especially vulnerable to hot weather. Older bodies can be slow to sense and respond to changes in heat, so seniors often don't start sweating until their temperature has already soared. Even when the body's cooling devices kick in, they probably don't work as well as they used to.