Tiny Sensors Use Perspiration to Track Health

Perspiration, also known as sweating or diaphoresis, is the production of fluids secreted by the sweat glands in the skin of mammals.
Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distributed over much of the body.

In humans, sweating is primarily a means of thermoregulation, which is achieved by the water-rich secretion of the eccrine glands. Maximum sweat rates of an adult can be up to 2–4 liters per hour or 10–14 liters per day (10–15 g/min·m²), but is less in children prior to puberty. Evaporation of sweat from the skin surface has a cooling effect due to evaporative cooling. Hence, in hot weather, or when the individual’s muscles heat up due to exertion, more sweat is produced. Animals with few sweat glands, such as dogs, accomplish similar temperature regulation results by panting, which evaporates water from the moist lining of the oral cavity and pharynx.

Primates and horses have armpits that sweat like those of humans. Although sweating is found in a wide variety of mammals, relatively few (exceptions include humans and horses) produce large amounts of sweat in order to cool down.

Sweating allows the body to regulate its temperature. Sweating is controlled from a center in the preoptic and anterior regions of the brain’s hypothalamus, where thermosensitive neurons are located. The heat-regulatory function of the hypothalamus is also affected by inputs from temperature receptors in the skin. High skin temperature reduces the hypothalamic set point for sweating and increases the gain of the hypothalamic feedback system in response to variations in core temperature. Overall, however, the sweating response to a rise in hypothalamic (‘core’) temperature is much larger than the response to the same increase in average skin temperature.

This wearable lab contains “microfluidics” designed to route fluids inside themselves in much the same way that microelectronics do with electrons. Specifically, the sensor directs sweat down a number of microscopic channels that are about 0.02 inches (0.5 millimeters) wide into compartments about 0.16 inches (4 mm) in diameter. Each of these chambers measures specific biomarkers, such as pH, lactate, chloride and glucose levels.