Dr Karl S. Kruszelnicki tackles life's myths, curiosities and absurdities.
Detox? Don"t sweat it

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1
In the good old days, horses would sweat, men
would perspire and women would glow. Today,
everybody wants to sweat to "get the toxins out"
of their body. Yes, sweat does carry some chemicals
out of the human body, but the real workhorses
of detoxification are the liver and the kidneys.
The human body operates best at 36.8'C, plus
or minus a narrow temperature range of 0.60C.
When it's hot outside, sweating comes into its
own as a magnificent cooling mechanism. So the
main job of sweat is cooling, not detoxification.
There are two main types of sweat glands. A
small number of apocrine sweat glands are on the
armpits, nipples and genitals. They start working
when you hit puberty, and give off chemicals
associated with courtship behaviour, synchronising
menstrual cycles in women who live under the
same roof, and marking territory (in animals).
But it's the two million eccrine sweat glands
scattered over practically all of your body that
spurt out the sweat that we know and love. About
half of them are on your trunk, a quarter on your
legs and feet, and the
remainder on your arms,
hands and head. They're
not evenly distributed - for
example, many more are on
the palms of the hands than
on the shoulders. This explains
why nervous people can have
sweaty palms.
Each of these sweat glands
is a tiny factory that filters
the blood to remove water,
salts and various other
chemicals, and then feeds
ibis liquid into a skinny

This item came from the Sydney Morning Herald
Goodweekend January 21-006 P7.

2
tube over a metre long. When you sweat, tiny
muscles squeeze on the tube and squirt out a
droplet or two of sweat - and can do this every
nine seconds. The tiniest breath of moving air
evaporates this sweat, and so cools you down.
The evaporation of one millilitre of sweat can
cool down about 500 grams of flesh by 1 'C.
On average, the evaporation of your sweat
accounts for about 20 per cent of your cooling
requirements. However, under worst-case
conditions (such as forced desert army marches),
your sweat will dump about 90 per cent of
your heat. Once you've acclimatised to the heat,
you can generate about two to three litres of
sweat an hour.
Sweat contains water and salt, and microscopic
amounts of potassium, chlorides, bicarbonates
and various immune system chemicals. Sweat also
contains various proteins, enzymes and amino acids,
as well as calcium, glucose, magnesium, lactate
and ammonia - and even alcohol, if you've been
drinking. And yes, microscopic amounts of various
trace metals such as manganese, copper,
zinc, cadmium, lead, iron, nickel
and aluminium have been
measured in sweat.
The bottom line is that the liver
and kidneys are the workhorses
that get rid of toxins, while sweat
glands cool you down. But blood,
sweat and tears are also
associated with hard work. The
American political activist Jesse
Jackson said, "Both tears and
sweat are salty, but ... tears will
get you sympathy; sweat will
get you change."

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