Not sweating at all might sound like a good thing given the problems we've discussed so far. But as we've pointed out, sweating is necessary to keep our bodies cool, so not being able to sweat is potentially dangerous. Some people lack this ability to sweat, a condition known as anhidrosis or hypohidrosis.
People with anhidrosis may get dizzy, flushed, nauseated and weak when exerting themselves, but barely sweat at all. A person with a mild case sweats less than what's considered normal, or perhaps sweats in fewer areas. Extreme cases affect the entire body.
Anhidrosis is caused by malfunctioning sweat glands, and there are many potential causes. Children born with it don't develop sweat glands at all, or develop very few of them. Nerve damage is another culprit. Diabetes, for example, can damage the nerves that control the sweat glands, and so can skin diseases like psoriasis. Other possibilities: certain medications and genetic disorders such as hypohidrotic ectodermal dysplasia (see sidebar).
What does it feel like? People with anhidrosis get painful muscle cramps known as heat cramps. They're also likely to experience heat exhaustion or get heat stroke, which occurs when the body's core temperature reaches 104 degrees Fahrenheit (40 degrees Celsius). Without swift treatment, heat stroke is life-threatening -- it can lead to a coma or death. Minor cases of anhidrosis can be alleviated by avoiding extreme temperatures and taking great care to stay hydrated and cool during strenuous activity. People with severe cases may have to avoid exercise or going outdoors altogether when it's hot.