How does sweating help humans to maintain a constant body temperture?

By sweating, your body removes some of the heat that is trapped in your body. When you sweat, water is released through the pores on your skin. The water/sweat that is on your skin contains some of the excess heat from inside your body. Eventually the sweat will evaporate or be wiped away, taking the excess heat with it.

Sweating is a homeostatic mechanism that allows us control our body temperature. Suppose during peak metabolic activity, one's body T rises significantly. Since water (sweat) has many properties including high capacity to absorb heat without increasing much in T, sweat in a way transports this excess heat built up in the body out of the skin to cool the body down. That's just one among other valuable functions of sweat.

If you're interested, you should check out "Becoming Human" to see the evolutionary reason behind the gradual losing of the hairs as we evolved into Homo sapiens. Cool stuff!

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As the sweat evaporates from your skin it takes some of your body's heat with it. Think about water evaporating, you always need a heat source - the sun, the stove, etc.- for the sweat to turn from liquid to gas it also needs heat which it pulls from your body. This in turn lowers your body temperature.

It does it with pure physics. Sweat is mostly water. When you heat water it evaporates. In the process of evaporation energy is used to convert liquid into gas. When our body overheats it starts to sweat. The excess heat energy from our body is used to evaporate the sweat, thus using up that energy (heat) and cooling our body down.

Water has what is called a high heat of vaporization, this means that it takes a lot of energy, to turn water from a liquid to a gas. As sweat on your skin evaporates, it takes a lot of energy with it. This removal of energy, cools the body.

The cooling effect of perspiration evaporation makes use of the very large heat of vaporization of water. This heat of vaporization is 580 calories/gm. Without this, the internal body temperature would kill a person. The skin will begin to sweat almost precisely at 37°C and the perspiration will increase rapidly with increasing skin temperature. Guyton reports that a normal maximum perspiration rate is about 1.5 liters/hour.

When our bodies get heated, we sweat, and when we sweat, our skin absorbs the moisture and cools us off again.

It lets you know you need to get to an air conditioned room.

Due to the high latent heat of vapourisation of water, the evaporating sweat tends to take up a lot of heat energy thus cooling the body in the proccess.