Body temperature control in humans is one of the most familiar examples of homeostasis. Normal body temperature hovers around 37 °C (98.6 °F), but a number of factors can affect this value, including exposure to the elements, hormones, metabolic rate, and disease, leading to excessively high or low body temperatures. The hypothalamus in the brain regulates body temperature, and feedback about body temperature from the body is carried through the bloodstream to the brain, which results in adjustments in breathing rate, blood sugar levels, and metabolic rate. In contrast, reduced activity, perspiration, and heat-exchange processes that permit more blood to circulate near the skin surface contribute to heat loss. Heat loss is reduced by insulation, decreased circulation to the skin, clothing, shelter, and external heat sources.