People commonly sweat in very hot temperatures, when exercising or doing some sort of physical exertion, or when they are nervous or under stress. The evaporation of the sweat from the skin cools the body. Sweating is also increased by nausea, the removal of fluids through perspiration reducing the amount of fluid in circulation in the body and (slightly) relieving the sensation of nausea. This is all normal and healthy.
Sweat is primarily water, but it also contains urea, the main chemical found in urine, and lactates, which cells produce when they burn sugar without enough oxygen. There are also mineral elements in sweat, including chlorides, potassium, calcium, magnesium, iron, zinc, copper, and even lead. Severe sweating can lead to depletion of these minerals. Sweat is more "watery" than blood.
There are about 2 million eccrine or "water-producing" glands on the surface of the human body. The palms and soles of the feet have the most eccrine sweat glands. Aporcine glands, which produce pheromones, are located around the genitals and under the arms.
What are the causes of bad odor?
Although eccrine sweat contains urea, it is mainly composed of water and sodium chloride (salt), and is therefore actually almost completely odorless to most humans, unless it is carrying some additional chemical the body is trying to get rid of.
Eccrine sweat glands also act as an excretion mechanism for the body. Some spices contained in foods including garlic, curry, and fenugreek can cause the smell of sweat to change. You may have heard someone say they ate so much garlic it's coming out of their pores. This is not just an expression, but what can literally happen when your glands start excreting certain substances.
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